Finally some results! But lets start with what I have done so far. Since my initial experiments with my scanner were somewhat successful and I had my new QFH antenna made and ready to go I just needed my Minikits weather satellite receiver to arrive and then I could try getting some decent images.

The kit arrived after just over a week and ended up costing me $NZ125 including shipping. This is far cheaper than any other kit I could find online, all of which you have to pay in Euros or US dollars.

The Minikits kit.

The kit is rather nice. It comes with a tinned double sided plate through hole circuit board. Several little bags of components including all the coils and ICs you need. It also came with an F connector to solder onto the board but I have chosen to use BNC connectors instead. It also comes with the instructions and the description of how the circuit works.

The kit uses an MC13135P receiver chip which is a complete FM receiver on a chip basically. There is also a TL072 op-amp and an MC34119 audio amplifier. All of the components are standard leaded types except for a surface mount NTC thermistor used as part of the automatic frequency control circuit to account for temperature variations.

You do need a few other things so I added the speaker, the signal meter, a AFC switch (the kit comes with a jumper) and the audio out connector. I also used full sized pots for the volume and squelch control since I will mount them off the board. The kit comes with trimmers to use on the board though. The kit runs off a 12 volt supply which is regulated down to 5 volts on the board for most of the circuit to use. I made a small power supply board with a 12 volt regulator on it and powered that from an old power supply from a set of old computer speakers. The used speaker I am recycling came from the same set of old speakers. The signal meter was a nice find. The first place I look for odd electronic stuff, Surplustronics, didn’t have anything so I headed up the road to the top of Queen Street to a real electronics junk shop. I have no idea what it’s called but it’s been there for years now. It’s cram packed with junk. Most of it is useless but the odd interesting thing here and there. Nothing is sorted. It’s all just in piles. I dug about and came up with this nice signal meter with a 0-5 scale on it. He wanted $3 for it. I had $2.20 in change (good thing I hadn’t bought a Mars bar that day) so he said close enough. It was unused and still in the bag!

Assembled kit set. The red thing is a plastic tuning tool.

Building the kit is easy. The instructions say it takes about four hours but I did it in two. All those years of working as an electronics tech to pay for my way through university came in handy! Once you have built it you need to set it up.

The way the receiver works is the incoming signal, which is around 137MHz, first goes though three bandpass filters. These eliminate any extra signals from getting through and just pass the weather satellite transmission frequencies that we want to receive. This is important in some places where there are strong pager frequencies nearby (people still use pagers – probably more reliable that Telecom’s XT network).

We then want to take the incoming signal and convert it down to a much lower frequency. This is called an intermediate frequency.  An intermediate frequency, or IF, is used because it is easier to work with and  filter on the lower frequency and because if a receiver converts all the frequencies you want to receive down to the same IF then all your circuitry from that point on can be optimised for just that IF frequency. This receiver uses the same IF most FM receivers use, 10.7MHz.

To get to the IF the receiver chip uses a mixer. The mixer takes the received signal and mixes it with another signal that we generate on the board. This signal needs to be 10.7MHz higher than the signal we wish to receiver. The mixer takes our signal and subtracts from it the received signal to get the 10.7MHz IF signal. This process is called Hetrodyning (which is probably what my friend Fing tells his friends he is doing when he comes to visit Auckland and we all go to the pub for lunch). The on board frequency is generated by a thing called a voltage controlled oscillator or VCO.

In this circuit the VCO is controlled by a coil, which gives a rough setting, and the tuning resistors, to fine tune to for each frequency.  The kit uses 25 turn trimmers for tuning. Each channel uses one trimmer. The kit only comes with one but you can simply add more and use a multi-pole switch to switch in the appropriate ones. For now I just have the one which I adjust for each different frequency when I need to.

The signal passes though various stages in the chip and eventually gets spat out as audio. There are two audio paths. One is to the audio amplifier chip which is controlled by the squelch circuit. The other is a line output to the PC sound card.

To set the receiver up you need to adjust the VCO to be 10.7MHz above the frequency you want to receive. The receiver needs to receive from 137MHz to 138MHz approximately. The tuning resistor needs to tune across that range.  If you set the tuning resistor to half way in it’s travel that would correspond to 137.500MHz. We therefore want the VCO to be oscillating at 148.200MHZ (148.2 – 10.7 = 137.5).

To set the VCO frequency you need to adjust one of the coils on the board. These coils have adjustable ferrite slugs in them that you screw up and down to set the frequency. They are fairly delicate and also metal near them will upset the frequency so you need to use a red plastic tool for adjusting these. This was available as an extra from Minikits cheaply.

The best way to know you have the right frequency is with a frequency counter. Unfortunately I don’t have one. So the next best thing is to use my scanner again. Because the coil is oscillating it is also radiating radio waves. If you hold the scanner close to the circuit board set to 148.200MHz when you adjust the coil and it hits that frequency you’ll hear it on the scanner.

With the VCO set this way you know the receiver should be receiving across the 137 to 138MHz frequencies over the 25 turn range of the trimmer tuning resistors.

Next the instructions say to attach a RF signal generator set to 137.500MHz to the antenna input and adjust the filters and output demodulator for the cleanest signal. Again, I don’t have a signal generator so instead I had to wait until I knew a satellite was overhead. With the antenna sitting out on the front deck railing I used the WXtoImg software to know when to listen and on which frequency. I used my scanner to be able to hear when the signal was there.  I then connected the antenna to the receiver and tuned the receiver to the right frequency and quickly adjusted the rest of the circuit while I still had a signal. This can take some time given the low number of passes per day and the short time the passes last. You have about 15 minutes in which to tune things.

To do this tuning I used my ocsilloscope on the audio output to see how clean the signal looked as well as by watching the signal meter and adjust it to give the highest signal as suggested in the instructions. This worked very well.

Initial setup and testing.

One interesting part of the circuit is the automatic frequency control, or AFC. This is quite clever and it will allow the receiver to account for the Doppler shift in the satellite as it passes towards then away from the receiver by adjusting the VCO.

You will see that the EeePC is displaying an image here but I found that it can’t actually decode the pictures properly. I think this is because I was using the mic input instead a a line in (which the EeePC doesn’t have) and so I wasn’t getting a proper signal.

The next thing to do was transfer everything over to my main PC and to put the antenna in a better position (on top of the guttering on the edge of my roof for now). With everything set up like that I finally got my first real picture.

The first image!

And this is what I got. The noise and blank part at the bottom of the image was me trying to tune things in as the satellite passed (from south to north). The horizontal lines were when I was adjusting things. In between though you can see a good image.

With more tweaking and tuning I am now getting nicer images. I am just using the basic settings in the software for now. I think there are a number of different settings to show you different things but I haven’t played with them must so far. These images are using MCIR map colour IR and an Equidistant Cylindrical  settings.

First good image.

I still need to manually tune hence the missing bottom to the image but this was a imagine received from NOAA 18 on 137.9125 MHz (that’s why so much of the bottom is missing – I had to turn that 25 turn trimmer a lot) at about 2pm.

The same satellite did another pass about 1 hour 40 minutes later and I got the image below.

Second pass by the same satellite showing Australia.

You can see how the satellite follows different paths on different orbits so you end up receiving differing pictures. Using some (free) software such as WXTrack you can actually see the path the satellite will take overhead. If the satellite is very low on the horizon you will get noisy images. The antenna needs a clear line to the satellite so obstructions in the way will degrade the signal.

So, what’s next? Well, I am still only using the one tuning resistor so for each different satellite frequency I need to re-tune the receiver. This won’t do as a long term solution. Instead of the idea that is given in the kit of using 5 tuning resistors all switched in via a rotary switch I want to try something a bit more automatic.

The kit does provide connection points for adding a phase locked loop or PLL for short. This would allow scanning across the whole frequency range then have it stop once it detects the appropriate signals. You can buy suitable experimenters PLLs that are micro controlled but these are rather expensive and I am trying to do this on the cheap!

I considered using a micro controller to switch between five or so pre-tuned frequencies. Because there are only a few satellites transmitting on fixed frequencies (the status of the satellites and information about them is available on the NOAA POES status site) you don’t actually need to scan the whole range. You can just step through fixed channels looking for a signal.  I could use a micro to switch each channel in for a brief period, say 2 or 3 seconds, and if a suitable signal was detected stay on that channel until the signal drops out again.

Switching in a set of preset tuning resistors can be done using a bilateral switching chip. A micro could control the switching. I then though that’s perhaps over complicating things so perhaps I can do it entirely using normal ICs.

My current plan is to use a 555 timer providing a slow clock pulse. These I feed into a 4017 decade counter (one of the first ICs I ever experimented with so a favourite). The outputs of the counter feed into a 4066 bilateral switch to switch in each tuning resistor in turn. They also turn on various LEDs to show what channel is currently selected. When a signal is detected the counter stops on that signal until the whole signal is received. This part I haven’t worked out yet. I was thinking of using the squelch signal but I don’t think this will work too well. Instead I might make a tone detector to listen for the tone you hear when the signal is coming in. The APT system used to transmit the images used a 2400Hz sub-carrier it should be possible to detect easily.

Progress so far.

So far I have got the clock, counter and switching working. You can see those on the breadboard in the picture above. I need to start on the tone detector. Perhaps using a LM567. My backup plan if I can’t get that working is to use an Arduino perhaps. Everyone loves Arduino!

Also I need a more permanent antenna installation. Perhaps a small mast mounted on the roof of my garage so I can put it there and get a nice, clear view of the sky.

And of course once done everything needs to be put into some nice housing.

Will update this with progress soon.

Now I will describe how I made a much neater QFH antenna to receive the satellite signals. My wooden one worked fine but it was not waterproof or particularly pretty or accurately made. So I decided to make a waterproof, prettier and more accurate one.

Again I followed the directions given here: http://www.g4ilo.com/qfh.html

I started off with the raw materials which I got from one of my most frequented places – Bunnings Warehouse. There are probably cheaper places to buy this stuff but Bunnings is convenient. I bought a 1m length of 32mm diamater PVC pipe and three lengths of black 15mm diameter Enduroflex pipe. I have no idea what that stuff is used for. Water piping I think. The PVC pipe cost NZ$15.51 and the black pipe was $11.16 for the three lengths although I only ended up using two of them. That black pipe incidentally is the perfect size for the barrel for a home made Nerf gun firing suction darts (a project for another day)!

I also bought some RG-58 (50 ohm) co-axial cable from Jaycar rather than the RG-6U I used on the wooden antenna. The The problem I had with the RG-6U is that the braiding isn’t copper but rather aluminium so it was impossible for me to solder the connection easily. The RG-58 is somewhat thinner diameter than the RG-6U which does mean the antenna is more easily bent out of shape but as my antenna will only be used occasionally it should be fine for now. The 15 metres of co-ax was $28.50.I cut the PVC down to about 800mm long and marked it up ready to drill the holes for the cross arms. I was very careful with the dimensions on this antenna. An easy way to mark around the pipe is to wrap a piece of printer paper around it ensuring the paper is square to the pipe by making it overlap itself perfectly as it wraps over itself. You can then mark off the place the sheet overlaps. You unroll the paper and the distance form the edge of the paper to the mark you a made is exactly the circumference of the pipe. It is then easy to mark off the quarter and half way points on the flat paper. Then you wrap the paper around the pipe once more to transfer those marks to it.

I then put the pipe on a nice flat surface and use the ended of a long, straight piece of wood to transfer the lines down the entire length of the pipe.

After carefully marking the pipe and measuring it several times I drilled the holes to hold the cross members. I first drilled a pilot hole with a 3mm bit then I used the spade bit to drill out a larger hole (sorry for the badly focused photo).

To make the holes a nice, tight fit I drilled slightly undersized then used a tapered reamer to enlarge the holes to the exact right diameter.

Once done you end up with mast finished. The positioning of the middle set of holes holes isn’t very critical as those arms just hold the ends of the cables in the correct place. Obviously you want them close to the mid point though.

I next carefully cut the six cross arms from the black pipe. Note the two different sizes for the two different sized loops in the antenna. I trimmed the ends square in the lathe (because I could, not for any technical reason) then carefully marked and drilled the holes in the ends. Looking at the plans you can see these holes need to be a fixed width apart to ensure the loops of the antenna are the correct size. They also need to be drilled at 45 degree angles to the mast so the cable has the correct spiral to it.

To drill the holes so they are at 45 degrees to the mast when installed you actually need to drill the holes in each cross member 90 degrees apart, one at either end of the support. Since the drill press drills down vertically all I did was drill one hole then push a piece of aluminium tube through it temporarily. Then, turning the tube around I simply adjusted it in the vice until the aluminium tube was parallel to my drill table. With it parallel when I drilled the vertical hole I could be sure the two were 90 degrees apart. When you push the crossmember through the mast you simply twist it so that one of the holes is at 45 degrees to the mast and the other will be aligned at 45 degrees too. You do have to twist it the right way though so that the cable is spiraling down anti-clockwise when viewed from above.

Because I might want to experiment with this antenna a little I didn’t want to glue the crossmembers fully in place yet so I am temporarily using some pieces of split ribbed tubing to stop the crossmembers moving in the mast.

In the top and bottom sets of holes I needed to file slots so that the cable could pass through into the mast. The holes for the arms at the ends of the mast I drilled so that the centre of the co-ax cable would be sitting at the exact right measurement given in the plans with the cable running along the outside of the crossmember , not inside it. Running the cable inside the crossmembers would of course be neater. But there is then no way to make sure the cable lies flat in the correct place. Does this make much difference? I have no idea! But the dimensions are given down to fractions of a mm accuracy so I decided to get things as close as possible.

I started putting the crossmembers in place and also soldering the connections. Shown here is the bottom most connection. That is the feed wire soldered to the shield of the bottom of one of the loops. I insulated the connection with waterproof tape then carefully pushed it into the mast and then pushed the crossmember fully home.

Similarly at the top I carefully soldered the connection inside the top of the mast once the loops and the crossmembers were all in place.  Notice the anti-clockwise direction of the spirals. I used lots of cable ties to hold the co-ax down flat across the crossmembers. Eventually I will remove the split tube and just glue the crossmembers in place once I know everything is correctly positioned.

To finish off the antenna I put a PVC cap over the top of the mast and I also made a quick and dirty stand from a scrap piece of wood and another off-cut of pipe that the mast happens to slide into perfectly. Eventually my plan is to hang it from a line suspended above my garage roof where it will have a clear view of the sky. The antenna might be connected to a line going around a pulley so I can hook the antenna onto the line and pull it up into position but still bring it inside if the weather is too bad. Either that or I will make a third, more robust version to permanently mount on my house roof.

With the antenna on it’s temporary stand I was able to move it about outside to see how well it would work. It works well when it has a clear line to the satellite down to very low on the horizon. The signal is very easily blocked though so building and even trees will cause you to lose the signal.

Now I just need my receiver kit to arrive so I can build that and really see how this works!

Update: The kit arrived! Read about it in Part 3.

I should point out that I am not a radio amateur, or HAM, as they are known. I am just an electronics tinkerer. Anyone with good, general electronics skills can do this.

Bender showing off my scanner.

One thing you can do is pick up pager frequencies. I pick up 157.950MHz easily at home which is a Telecom pager frequency. It sounds like a random collection of bleeps and bloops – R2D2 with his knickers in a twist. Apparently with a simple mod you can break out the unfiltered audio (called the discriminator output) in the scanner and then, using some software called PDW, decode the pager signals.

Even though the mod is easy to do (if you are electronically inclined) looking at other peoples pager messages strikes me as being terribly uninteresting, kind of like having to overhear other peoples one sided phone calls on the bus, so I haven’t tried this modification myself.

One other thing I could try (after doing the discriminator mod above) is receiving AIS signals. These are the identification signals used by ships. Since I work in the city and it’s not too far down to the port I should really try seeing if I can receive them. Perhaps the Northern Steamship Company pub might be a good place to try!

The frequencies used are 161.9750 for AIS1 and 162.0250 for AIS2. Apparently you can then feed the signals into a sound card on a PC and using some software like Shipplotter you can track the movements of shipping in your area. Something to try another day.

One thing I did want to try, being interested in all things to do with space and space technology, is receiving weather satellite transmissions. Now, before I start I should say that you cannot actually decode the weather satellite transmission using this particular scanner. You can HEAR the signals but you cannot generate any kind of useful pictures with them. Well, I have been unable to. But given that you can hear them was enough to start me off on this project.

Lets start with some background first.  Up there, in space (well, low earth orbit 850km up), there are some weather satellites. Both the Americans and the Russians have them up there, the NOAA and the METEOR satellites respectively. There are others of course but the NOAA are the ones you can easily receive signals from so they are the ones I am listening to. These satellites are continuously transmitting signals down to earth using a system called APT. The Wikipedia Automatic Picture Transmission article gives you all the background you need but here are the basics.

The NOAA satellites are in a polar orbit around the earth and as they orbit they are continuously scanning a line beneath them 3000km wide and transmitting this line back to earth. Being in a polar orbit means each satellite will pass over the entire planet as the earth rotates beneath them. As a satellite comes up over the horizon and passes overhead a receiver on the ground can start receiving these lines, decode them in sequence and build up a picture. Due to their low altitude these satellites orbit rapidly and each satellite will make several passes over your location each day.

The signals are transmitted on a group of frequencies around 137MHz.  The actual picture received  contains two views of the earth below the satellite – one in visible wavelengths and another in infrared. A line is scanned twice every second and each line contains the image data as well as non image data. This system has been used since the 1960s so it is quite remarkable it is still in use today. You can get up to date information about the NOAA weather satellites from this status page.

To receive the pictures you need three things: a receiver, an antenna and a PC (with a sound card and some software to do the decoding).

First, the receiver. As I mentioned above my particular scanner (or indeed most scanners) isn’t suited for doing more than hearing the signals but it is enough to let me work on the second piece, the antenna.

The antenna obviously needs to pick up the 137MHz signal the satellites transmit on. It also needs a wide receiving pattern as it has to be able to pick up the signal from horizon to horizon. The signal from the satellites is circularly polarised so the antenna must be designed in a particular way to receive the signal. Two suitable antenna designs are the turnstile antenna or the quadrifilar helix antenna (QFH).

Looking around online I came across several references to the QFH antennas with very good instructions on how to make them specifically for receiving weather satellite pictures. The design I decided to use was from here: http://www.g4ilo.com/qfh.html

Because I didn’t know if I was going to be able to receive anything I made my first QFH using materials I had on hand, namely wooden dowels. I made an antenna using the instructions and dimensions given above. I used RG-6U coaxial cable as that was easy for me to get quickly in order to try things out. I first tried using the antenna indoors until a friend pointed out that the metal roof would block the signal (a duh moment) so instead I simply took the antenna outside and hand held it in order to try it out. To my amazement it worked! I could hear, albeit with a lot of noise and static, the satellites transmitting their signals.

It’s worth mentioning that because the satellites are constantly orbiting you need to know exactly when a satellite will be passing over. This brings us neatly to the third thing you require, a PC with a sound card and some software running on it.

The software I am using is called WXtoImg and it is available to download and use for free (you can also pay to register it for additional features). Interestingly it seems to be written here in New Zealand. This software does two things. It decodes the received audio signal and formats that into usable images and it also tells you when (and where) the next satellite will appear.

Another useful piece of free software is WXTrack by David Taylor. This software lets you see exactly where satellites are over the earth at any given time.

Both of these programs require you to download up to date satellite tracking information called Keplers but this is well explained and easy to set up.

Since I could now hear the signal and I had downloaded and installed the appropriate software I rigged up a temporary support to hold the antenna up outside my window were it would have a (reasonably) clear view of the sky and attempted to feed the signals into my PC.

My quick and dirty wooden QFH antenna and dodgy mounting method.

The results were not good (it wooden work)! This I expected and the problem isn’t the antenna itself but the limitations of my scanner.

There are various problems with using scanners for receiving weather satellites. Other weather satellite sites explain the problems better than me but to summarise the main problem is due to bandwidth. Now bandwidth, as I understand it (and I could be wrong!), when talking about receiving weather satellite transmissions is the difference between the lowest frequency and the highest frequency that you need to be receiving signals over to get the full signal. A scanner like mine is designed for receiving voice signals. Voice signals don’t need a very wide frequency range so we say the scanner has a narrow bandwidth. The bandwidth of a scanner like mine is about 15kHz so the scanner will filter out any signal outside that range around the main frequency.

The satellites transmit their signal over a much wider range spread around the main frequency, i.e. is has a wider bandwidth. To accurately receive the entire weather satellite signal you need a receiver with a 30kHz to 50 kHz bandwidth. So in effect my scanner is blocking out part of the signal. We basically lose information from that lost signal so the software can’t build a good picture from it.

Other issues with a normal scanner are sensitivity, how strongly it picks up the weak satellite signal, and selectivity, how well it picks up only the frequency you want. Another, more subtle problem, is the doppler shift caused by the movement of the satellite as it passes overhead. This causes the frequency to shift as the satellite passes overhead.

All these issues mean my little scanner isn’t up to the job. To really demonstrate this here is what a properly recorded signal of a weather satellite should sound like: http://n8imo.com/APT/images/N14.WAV (from http://n8imo.com/wefax4.html).

What I get is this: http://www.asciimation.co.nz/misc/06250521.wav\

Image produced by the scanner.

My friend Dave wanted to see a picture of what the scanner produced. This is the best that I ever managed to get. Mainly noise. With some vague picture in the middle as the satellite passed right overhead.

So when people say a normal scanner won’t work, they are right!

The next thing to do is sort out a proper receiver. There are a number of options here. You can buy a scanner that does have the correct bandwidth but these are very expensive. Or you can buy a ready made receiver just for receiving weather satellites. These are also expensive. Finally you have kit receivers you buy and assemble yourself. Being an electronics tinkerer this is what I was after. There are various kits on offer but I chose the Minikits weather satellite receiver.

This receiver is very reasonably priced, should do everything I want and the company is more or less local (well, Australia) so I was able to pay in Australian dollars rather than US dollars or Euros which tend to work against someone earning NZ dollars. Shipping was also cheaper and faster.

I ordered the kit last week and it should arrive any day now so I will be building that as soon as possible.

In the mean time, having proved that a QFH antenna would indeed work I set about making a more accurate, more weather proof version.

Will describe that in part 2 here.

http://www.asciimation.co.nz/bb/2009/10/18/a-rocking-horse-for-sophie

With time moving on I had to really move to get the rocking horse done. After protecting the foam with the tin foil I applied layers of fibreglass and polyester resin. I built up a nice, thick skin of glass all over the horse.

Layers of fibreglass to make a shell.

After the fibreglass shell had hardened I gave it  a quick sanding just to remove any sharp bits then set about adding in Horseome Paul’s super secret feature – a hidden hiding place where Sophie can keep things. The cavity was made form a piece of PVC piping. A hole was cut in the horse and the pipe gently inserted.

Gentle insertion of secret hiding place.

Once the pipe was fully inserted the excess was trimmed off with a cutting disc on a Dremel.

Cutting off the excess.

Once the cavity was done I then covered the body in several layers of 5mm thick upholstery foam. This was glued on using Ados F2 spray contact adhesive. I put extra layers on the head for some extra padding in case of face plants by the young rider!

Covered in foam padding.

Next I had to figure out how to cover him in fur. A visit to Spotlight (a material and craft super shop – kind of like Bunnings for girls) provided me with some great fake fur and some pink frilly stuff for the mane and tail.  I roped in a friend to help with the sewing (at the cost of making her dinner). I wrapped the horse in plastic from an old plastic bag then wrapped that in layers of brown packing tape. The idea is to make up a tape shell that you can then cut off with scissors and cut to form flat pattern pieces that will exactly match the three dimensional shape you are trying to cover. I was going to buy a sewing machine and learn to do all this myself but with only a few weeks before Christmas I ran out of time.

Wrapped in plastic and tape.

So, with time running short my friend Dani came over to help with the pattern making and sewing. One look at Horseome Paul though and we decided it was going to be trickier than we though. Dani makes quilts which are flat. A three dimensional horse was a much trickier problem. We decided I should try to find someone with a bit more experience to help. Still made her dinner though

As it happened there is an alterations place near to where I work (errr, used to work as I was made redundant just before Christmas). I popped in there and talked to a woman who didn’t speak much English but after must gesturing and explaining she realised what I wanted to do and said she could help. I took the horse and material along to her and she sewed on the covering for me in a very short time and for an extremely reasonable price! She also made a bridle and sewed on buttons for eyes and even gave him a little charm necklace. He has a zip running down his back so the fur can be removed if needed.

Horsey head!

In the mean time I completed the wooded base. I originally painted it pink but in the end repainted it white and the pink become overwhelming! I attached some cardboard stickers I got from Spotlight to give some detail and to put Sophie’s name on the base. They were supposed to be self adhesive but I found I needed glue to get them to stick. Finally the body was simply bolted down to the base and held with large fender washers and Nylock nuts.

So here is the final product!

Horseome Paul is complete!

I ran out of time to make a saddle but I think he doesn’t really need one anyway. Christmas day is today so we shall see what young Sophie things in a few hours or so! Hopefully it doesn’t scare her!

Oh, that secret hiding place. Well, you can get to it by simply unzipping the zip under the tail a little. I am not sure my sister is going to approve…

And finally, 6 months later, an actual picture of Sophie on her horse. Yes, it is still bigger than she is!

Sophie aged 2 years 5 months (or so). Horse aged 6 months.

I decided to make the base rocker from wood and build a horse approximating shape on top of that for Sophie to sit on. The horse is made from polystyrene with pool noodle legs which is then covered in fibreglass to form a tough but light shell. The shell will be covered in foam then given a horse skin coat (that makes me think of ‘It rubs the lotion on its skin…’).

First I needed some polystyrene blocks to carve up into the basic shape. A sensible person would get some solid blocks from some sort of specialist polystyrene shop or something. I decided instead to glue together a few sheets of underfloor insulation foam since that was easy for me to get from Bunnings (where I seem to end up several times a month for some reason). I glued the sheets together using Ados F2 spray contact adhesive. The legs are made from sections of pool noodle.

Foam blocks and pool noodle legs.

Once I had the foam blocks I needed a way to cut them so I threw together a hot wire cutter. This is simply a wooden frame with a handle, kind of like a hacksaw frame. Stretched across the opening of the frame is a piece of nichrome wire. I use small screw eyes to attach it and at one end have a spring to keep the wire under tension. If you try to attach the wire to the screws eyes directly when it heats up it will expand and go slightly slack. The spring ensures it is always taut. A wire runs from either end of the nichrome and attaches to my car battery charger. At 12 volts the wire draws about 1 and 3/4 amps of current.

Hot wire cutter.

Next I drew something vaguely horse shaped on some cardboard then cut that out and transferred the shape onto the blocks.

Template and shape draw on foam.

Once I had a basic outline I used the hot wire cutter to remove anything that didn’t belong on a horse. Then after the basic shape was cut out I used a long knife to cut holes in the base of the body to push the legs into. I then used a 40 grit sanding disc on an angle grinder to sand the basic shape smooth. You need a gentle touch doing this as the disc will eat into the foam rapidly.

Basic shape cut and sanded.

Since the horse was taking shape I decided he needed a name. The horse is named in honour of an awesome ex-workmate of mine, Awesome Paul (so called because he is so awesome). The horse is of therefore known as Horseome Paul. Not many people can say they have a rocking horse named after them. Not sure many people would want to…

Once the shape was done I cut and pushed wooden dowels down the hole in the middle of the pool noodle legs. These extend right into the body to make the legs nice and strong. I drilled the ends of the dowels and inserted in some long 8mm bolts with the heads removed to turn them into threaded studs. These studs will attach Horseome Paul to the base. They are held in with extra strength Araldite epoxy.

8mm bolts glued into wooded dowels in the legs.

Next I started work on the base. First I drew a rocker shape onto some 6mm thick MDF to make a template. I used some scrap cardboard and a steel rule curved against a large steel block to form half of a smooth curve in the rocker. Once that curve was drawn on the cardboard I cut that out and transferred the first half of the curve to the MDF. I then turned the template over to draw the same curve on the other side of the rocker. The MDF template serves two purposes. First it gave me something to trace around onto two pieces of wood to give me a line to cut out with the jigsaw to form the rockers. Then I was able to screw it to the roughly cut wood and use the MDF as a guide on a ball race router bit to make the rocker edges square and identical. When tracing around the template I use a wide Sharpie marker to give a nice thick line. I then cut around the outside of the line meaning the rough rocker is about 1mm over-sized all around.

Template for the rockers.

The routing takes some explaining. What I do, and this is probably dodgy as hell, is bolt my router to a flat piece of MDF to serve as a base. I then screwed that to my temporary work bench I was using (a bit of chipboard sitting on a panelbeaters frame). This holds the router nice and firmly upside down with the bit facing upwards (Note to self :  I really must make a proper router table someday). I then screw the MDF rocker template firmly to the roughly cut rocker making sure it is lined up so the 1mm extra is even all around. Then I run rocker against the router bit (making sure as you push the shape around that the tool cuts INTO the wood) with the bearing on the tip of the bit running against the edge of the MDF template. Because the bearing is following the edge of the template the wood will be cut to the exact shape of it too.

Routing around the edge of the template.

Once routed out the two rockers are almost identical. Just to be absolutely certain I screwed the two pieces together then sanded the edges together to make them smooth.

Random orbit sanding the two rockers together.

With the two rockers made I then cut two small supports that are screwed to the inside of the rockers. The tops of these supports were cut with a curve on the top face to match the curve on the rockers. Two wooden dowels attach each end of the rockers together. These are screwed in place then small wooden plugs were glued over the screw holes. Wooden slats were then screwed across the rockers, the outer two being slightly thicker than the middle ones so the legs can bolt down onto them.

Base completed.

While Horseome Paul is off his rocker(!) a temporary MDF board drilled to match the holes in the rocker base keep the legs fixed in the correct position so the bolts will line up once he is fibreglassed. Without this the legs might shift position during the glassing process then not fit through the holes in the base.

Temporary leg support.

One final detail was making a handle to go right through the head. The handle is just a piece of dowel. It does need to be removable though so later on I can fit the horse suit over the body. I found a piece of PVC pipe the dowel slides nicely into. I pushed the pipe through the head and made sure it was flush on each side. When the body is done the dowel will slide into this and be glued into place (or perhaps wrapped in tape and just held by a friction fit).

Handle and PVC pipe being inserted. Went right through! Didn’t hit the brain!

Finally before fibreglassing I needed to cover the polystyrene foam to protect it from being eaten by the polyester resin I was going to use. To do this I glued tin foil all over the body to form a barrier to the resin. By the way the polystyrene ears  are just there to remind me that I am making a horse and not a sheep/dog/cow. The proper ears will be sewn on at the end along with a mane, tail, bridle and saddle.

Ooohhhh, shiny…

Finally fibreglassing could begin. To be continued soon.

Part two is now available here:

http://www.asciimation.co.nz/bb/2009/12/25/finishing-sophies-rocking-horse-before-christmas-just

The ladybird I was going to copy.

My idea was to make the bookends with ladybirds like the one shown above but with LEDs in the wings to make them light up at night. Originally I wanted these to be solar powered so that they would charge during the day and glow at night in the same was as solar garden lights. I did experiment with that a little but found there isn’t enough light indoors to reliably make this work. For now I am using a small power supply instead but I might revisit the solar idea later.

I started by making the base of the bookends. These are made from MDF and quarter round moldings. These were pretty quick and easy to knock up. I then painted them with a lot of coats of gloss white paint. On the base I glued some sheet rubber to stop the bookend from sliding about.

The wooden bases made from MDF.

After I made the bases I started on the ladybirds themselves. These were made from more MDF cut out on a band saw into the basic shape. The wings are made from white acrylic sheet cut to the appropriate shape. These were sanded to make them diffuse the light from the LEDs I was going to use to make them light up. Each wing is held to the wooden base by two screws. There are two holes in the bodies that allow the LEDs to be inserted and shine through the wings.

The ladybirds and their acrylic wings.

Once the bodies were made (and painted pink) I glued small pieces of felt onto the face. Two of these cover the screws that hold the wings on. On the back I inserted the  LEDs and their resistors. These are held in place with hot glue. In the center of the body I epoxied a threaded brass stud which is used to secure the back. The backs contain a power socket and are made from the lids of small plastic screw jars.

The back of the ladybird showing the LEDs and threaded stud.

The ladybirds are attached to the bases with two short lengths of brass rod covered in clear plastic tubing which spaces the body out from the base. These were epoxied in place.

The power socket in the backs are attached via short wires then the back is put in place over the  brass stud and held on with a nut and a dome nut. Using two nuts allows me tighten them together to lock them in place so wht backs won’t come undone.

    The back in place.

With the backs on it was a simple matter to make up some power cords. I use a small 5 volt  wall plug power supply. The LEDs are only drawing 20mA each so the power supply doesn’t need to be very big at all and the whole thing uses very little power. The LEDs make the wings glow very nicely. It is a bit tricky to capture in a photograph though!

And these are the finished bookends! Along with some books every little girl should read. Sophie is a little young now but she’ll grow into them!

 

 

The finished SV Chronometer.

Time. We are all obsessed by it and it catches up with us all in the end. Especially women who don’t moisturise their elbows properly! I have my own little obsession with time. I often have a stop watch in my pocket, just so I can time things, I wear a 24 hour analogue watch (they are cheap on eBay!) and I get very, very annoyed that all the clocks in my house all show different times! You can set them all to the same time but eventually they all drift.

For example the exact time now is 17:34. The clock/weather station beside my PC shows 17:32. My wristwatch shows 17:35. My mobile phone shows 17:32. The living room clock shows 17:37. The microwave shows 17:35. The video shows –:–. And my Spanked Woman Rotating Legs clock shows 8:55. I suspect her batteries have gone flat! Speaking of time you might need a bit to read all of this. It is a somewhat rambling discussion of how this thing works!

The drifting problem is something I just have to live with. I have no control over the actual timepieces so they are all going to drift over time and I know I have to keep resetting them. They question is when I do reset them what do I reset them to? What is the correct time? This little project is to solve that problem.

I decided to build a stand-alone clock that I can use as a master time source to set all my other timepieces to. All it has to do is show me the correct time but I wanted it to be interesting to look at and interesting to use. A plastic box with an LCD display on it would be effective but not nearly as much fun! I decided to build some kind of mantel clock and I wanted to base my design on an old art deco Hammond clock. The time is displayed on a screen inside the box which is only visible when the user peers though the eye pieces and cranks a handle on the side of the casing. The name of the device, SV Chronometer, comes from the fact that it is using GPS satellites to receive the time. In GPS language the satellites are referred to as Space Vehicles.

There are various ways other to get accurate time. Radio clocks are one method. Network Time Protocol (NTP) is another. Accurate time signals, called PIPS,  are often broadcast over radio stations. And there are speaking clocks available as well. The Measurement Standards Laboratory has a list of the various time standards available here in New Zealand.

To be honest my PC would probably be the easiest way to get an accurate time signal. Microsoft provide simple(!) instructions for setting up Windows XP to use NTP. As my computer is always on and always connected to the Internet I should always have an accurate time source. Instructions on the easy way to do this in NZ are available from MSL. Another easy way to get accurate time in Auckland at least is the bus stops. I suspect these might be using GPS time also as they are always in sync with my watch!

I should point out here that when I say accurate I am meaning only to within a second or so. I am using the time to set physical clocks some of which can only be set to within a minute or so accuracy anyway. If all my clocks are accurate to within a minute I am happy.

Once upon a time I worked for Navman,  a company that makes GPS navigation devices. Having played with GPS there and knowing a bit about how it all works (for a REALLY good explanation have a look at the Trimble GPS site) I knew you can get a very accurate time signal from a simple GPS module. I happened to have such a module from my time at Navman. Actually as it turns out that one was a lame duck but I managed to find an exact  replacement cheaply on TradeMe.

  GPS Module.

This particular GPS module is pretty simple. It has an onboard antenna as well as a connector to attach an external antenna. It runs off 5 volts and it has a very simple serial interface. I think most GPS modules available these days work in a similar way. The serial interface on this module outputs NMEA 0183 sentences. Basically the module is spitting out ASCII text that is giving you the GPS information. There are different sentences containing various pieces of information. Things like position, heading, speed, satellite information and, of course, time. Not all receivers give out all of the different sentences but time is one of the most basic so I think all GPS modules should have this available. Some pieces of information are available in multiple messages. Here is a complete list of the NMEA messages available.

The first thing I did was connect up my hand-held Garmin eTrek GPS unit to my PC using it’s serial cable. I was easily able to get that working and see the raw data in HyperTerminal. Next I tried connecting my Navman module up to the serial port on my PC to see what sentences it was giving me. I used a MAX232 chip between the module and the serial port to do the signal level conversion. I was rewarded with a nice stream of NMEA sentences.It provides the GPRMC, GPGGA, GPGSA and GPGSV messages.

One thing about the Navman module is that it runs at a very high serial speed, 57600bps. This was to make things interesting later on. From the NMEA messages I was getting I could see I could pull out the data I wanted. I can use the GPRMC message to get th time and the GPGSA message to get the fix accuracy.

This is an example of the actual GPS raw data the module outputs:

$GPRMC,051735.997,V,36000.0000,N,72000.0000,E,0.000000,,041108,,*34
$GPGGA,051736.997,0000.0000,N,00000.0000,E,0,00,50.0,0.0,M,26.2,M,0.0,0000*41
$GPGSA,A,1,,,,,,,,,,,,,50.0,50.0,50.0*05
$GPGSV,3,1,09,16,71,075,,20,52,293,00,23,48,221,,31,30,122,*70
$GPGSV,3,2,09,01,21,068,,13,20,230,,25,17,271,,06,14,037,*7E
$GPGSV,3,3,09,03,12,025,*47

Once I knew the information was there the question was how to get at it inside a stand-alone clock. I decided I could use a PIC16F628 microprocessor to receive the NMEA messages from the GPS module then parse them to get the bits of data I wanted. The PIC is well suited for such a job as it has a built in serial port, it’s own memory and it can easily be programmed (using assembler) to drive an LCD module which is what I decided to use to display the actual time.

Circuit and GPS module during testing.

Basically how it works is the GPS module sends out a group of NMEA messages every second. The PIC receives the serial data and writes it all into an internal buffer. I maintain an index to my position in the buffer. NMEA sentences can vary in length and the PIC only has limited memory but I worked out that the information I need is always in the first 13 bytes of the message. I made my buffer long enough to fit just the bytes I need. As the bytes of the sentence are received from the serial port they are put into the buffer until the buffer is full. If I receieve a ‘$’ character I restart at the beginning of the buffer as I know this is the start of a NMEA sentence. When the buffer is full everything else is then dropped.

As the bytes come in the PIC looks out for a ‘*’ character in the sentence. This happens regardless of whether the characters were written to the buffer or not. This character indicates  the check sum at the end of the NMEA message. I don’t use the checksum but I do use this character to indicate  I can examine what I have in the buffer from the message I have just received.

By examining the first few characters in the buffer I can determine what sentence I received. If it is one I am interested in I then copy the relevant bytes from the buffer into storage variables. . In my case I simply want the time, which is always UTC time, and the fix information, which tells me how accurate my satellite fix is. 

Because the Navman GPS module is running at a fast serial rate I found I didn’t have much time (measured in clock cycles) for parsing the messages. Luckily there was just enough time to extract out the time and fix data. It might have been nice to get the date also but that would cause other problem later on when I need to work out what time zone I am in.

Even though the serial data itself is transmitted very quickly the burst of data only happens every second. This gives me lots of time to actually manipulate and display the data between bursts once I have it.  To know when I can start displaying data I use one of the PICs internal timers. Timer 1 is set up so that it is reset each time a byte is received from the serial port. As data is received the timer is being continually reset. Once the serial data stops however the timer is left to run and eventually trigger an interrupt and I set about displaying the data. This will happen once a second after the data burst from the module.

Originally I was going to have the clock display as much information as I could. GPS could give me the location, heading, speed over ground, etc but really none of this information is very useful on a mantel clock that doesn’t move! In the end I decided to display only a minimum of information. The clock will show me the current UTC time, the time zone corrected time and the fix information. Time is displayed on a  2 line LCD display. The fix information is shown on the analogue meter on the front of the clock. When you don’t have a GPS fix the module will still output time but it is its own internal time. This is probably accurate enough for my purposes during the periods when the clock doesn’t have a real GPS fix.

Assembled on back plate.

Displaying the time on the display makes use of some simple LCD routines I wrote for the PIC. The UTC time is displayed almost exactly as it was received from the GPS module only formatted in hh:mm:ss 24 hour format. The local time is displayed by adding on a  time zone correction to the UTC time.

That was actually an interesting problem. My clock won’t work for all time zones because I had to simplify how I handle the time zones in the PIC and also due to my almost non-existent user interface. I don’t actually store a time zone as such. All I do is store a value from 0 t0 23 in the PIC to represent the hour correction that needs to be added to the UTC time. This is enough to cover most of the time zones in the world as most are at hour offsets from UTC. There are a few odd time zones in the world with half or even quarter hour differences. I figured the chances of me moving to such a place is slim!

To change the time zone I have a simple push button on the back of the clock case. Each push of the button increments the internal value. When it goes above 23 I reset to 0 again. This value is stored in EEPROM on the PIC so even if the power goes off it remembers your time zone when it restarts. To display the local time I simple add on this value to UTC. This is where not displaying a date makes things very easy. Being able to correctly show a local date worked out from a UTC date with a time zone correction is actually quite tricky. You need to take into account if the time zone is a positive or a negative offset then you need to adjust the day appropriately. When you adjust the day you need to account for the start and end of a month and adjust that appropriately. And once you do that you need to account for leap years. It all starts getting complicated and needing look up tables and so on which is a little more than my poor PIC can handle. Also I generally know what day it is anyway! You also have to account for daylight savings time which is another complication if you wish to do it automatically. On my clock you simply change it manually. Hell, it’s only 2 button pushes once a year and 22 button pushes six months later! Or is it 23? I am always off by 1!

The display (showing ‘Estimate’ instead of the UTC time).

The other main parts of the circuit don’t involve the PIC at all. The first is simply the MAX232 chip which I left in circuit between the GPS module and the PIC. On the back of the clock case is a RS232 port so I can connect the clock to any PC and see the raw NMEA messages if I want to. The second is more to do with the aesthetics of the clock which take some explaining.

The outer housing of the clock is obviously inspired (actually shamelessly copied) from the art deco Hammond clock. It is made from MDF which I then paint with thinned down polyurethane as a sealer then I spray ti with gloss black enamel paint. I didn’t want a simple clock face though. That would be far too boring. Instead what I have is a box you have to peer into in order to see the display. The front plate is painted steel and the eyepieces were made from a set of old, broken binoculars I removed the lenses from. To make the display look distant from the user and give the insides some depth there is a periscope system made up of two mirrors inside the casing . The display isn’t actually behind the eye pieces but is instead at the bottom of the casing and you are viewing it via the mirrors.

The inside showing mirror periscope.

To further obfuscate things (and this is where the interactive part comes in) the display isn’t actually visible if you just peer into the box. To actually read the time you need to crank a handle that is fixed to  the side of the housing. I was inspired by old fashioned “what the butler saw”  machines (actually called Mutoscope machines). Originally I played around with a mechanical shutter system where the crank flipped a little metal plate up and out of the way of the display so you could see it. The plate  was ‘bounced” by a cam so that you couldn’t simply turn the handle to one position to lift the shutter out of the way. You had to be actually rotating the crank for the screen to be visible.

The flywheel and switch.

The mechanical system worked but was finicky and also it made a horrible rattling noise! It occurred to me I could achieve the same effect electronically. Since the box is almost light tight and dark inside you have to use an LCD screen with a back light in order to see the display. To simulate the flickering effect I simply turn the back light on and off!  It worked out to be an elegant solution.

The crank handle is held to the case on a bearing carrier (something from something I junked so long ago I can’t remember what it was). I made the handle from a piece of steel suitably cut and drilled welded to an 8mm shaft. The shaft is held in place by a hex nut on the inside of the case. Attached to the inside of the case wall is a micro-switch with a lever on it. The lever runs against the hex nut and as the nut turns the switch is turned on and off six times per revolution. It also makes a great mechanical clicking noise which adds greatly to the whole cranking experience. To make the crank feel balanced I made a heavy lead fly wheel by melting down collected wheel balancing weights (I must admit I have a habit of collecting them off the road) and casting a rough disc. I machined that on the lathe to make a nice, heavy flywheel. One side has the lead hollowed out to help balance the handle and give a nice, smooth turning motion. Machining lead is not really a nice thing to be doing so I made sure I was wearing gloves, face mask and goggles (which you do for any machining of course). By keeping the speed right down I avoided chips flying all around the workshop and when I was done I was able to collect all the stray lead pieces and re-melt them into one lump. The lead is very easy to machine being so soft. The flywheel was then painted black to seal it.

Machining the lead flywheel.

The LCD back light isn’t connected directly to the micro switch. If I did that then you could stop the handle in one of 6 positions and read the display which ruins the interactivity of the whole project. Instead the switch is connected to a small circuit. The circuit uses every electronics hackers favourite friend the 555 timer! The timer is used to send a fixed length pulse via a transistor switch to the back light to turn it on briefly. A largish capacitor is connected across the back light LED to smooth out the pulse so instead of the display harshly flickering on and off it tends to rapidly fade in and out. The 555 is wired up slightly differently to what would be a normal monostable setup though to account for the fact that the trigger pulse can be longer than the timed pulse. Normally the trigger has to be shorter. This addition means stopping the crank in a position where the switch is pressed still only results in one quick pulse rather than the back light staying on.

The meter on the front of the box is used to display the fix information as previously mentioned. The meter will show no fix, a 2D fix or a 3D fix by flicking the meter needle on a 0 – 400 scale. 0 – 100 for no fix, 0 – 200 for a 2D fix and 0 – 300 for a 3D fix. I use the PICs built in PWM module to generate a 25%, 50% or 75% PWM signal that drives the meter to the correct position. If you have no fix the LCD will also display ‘ESTIMATE’ for the UTC time. Since the clock is updated every second between data bursts the meter needle flicks every second also. 

One quirk of the meter is when there is no fix the meter needle doesn’t move properly back to the zero position. This is due to it being 1, old and 2. dropped. Several times! The back of the meter housing was shattered so I had to repair it with a small piece of plastic. I have developed a habit of coming up and tapping the glass on the front of the meter when there is no fix to unstuck it and get it moving properly again. I find this just adds to the character of the clock!

A further addition is a simple LED inside the box which flashes in time to the meter on the front of the box. I used an ultra bright orange LED and this creates a nice, neon like glow that at night is visible flashing deep inside the box when you are lined up just right with the eye pieces.

Back plate.

On the back of the casing is a simple panel with connections for power, the external GPS antenna and the serial port as well as the time zone push button. The power supply has a bridge rectifier and a regulator so you can plug any ac/dc power supply up to about 15 volts or so in to power the clock. You can use any cheap power supply such as an old phone charger or wall power supply. The serial port is wired up to use a straight through cable. The external antenna connection means I can use an antenna on the roof to get a nice 360 degree view of the sky although I find it actually works pretty well inside on the window sill even though the view is limited. An external antenna is required since the actual module is mounted inside the box and it has no view of the sky.

Closing the back showing the internal layout.

And here is a link to a little YouTube video of the SV Chronometer in action. It is very hard to film it on my digital camera in such a way to show exactly how it works but hopefully you get the idea from this.

Part one of this project is available here:

http://www.asciimation.co.nz/bb/2008/04/19/building-a-wimshurst-machine

There were a few changes made to the machine since the last post. The main one was I discovered glass Leyden jars don’t work very well! Well, mine didn’t at least. I re-made the jars using plastic containers and these seems to work much better.

Plastic Leyden jar.

They are made the same way as the glass jars and the inside and outside are covered in aluminium tape. I machined up some plastic discs on the lathe to use as lids. Using the original plastic seal the lids fit tightly to the top of the jars. I used some copper foil tape to ensure there is a good contact between the foil on the sides and the base of the jar.

I also made sure the main discs spin true on the hubs.  Between the hub and the discs I use three small rubber O-rings. These allow me to make sure the disc is spinning true by tweaking the tension on the adjusting screws. I made a temporary jig and using a DTI (dial test indicator) was able to measure the run-out on the edge of the disc and adjust it until this was minimised. You can never get it perfect but this step helps a lot.

Adjusting the main disc run-out.

Once I had the discs and main supports made I started on the base. I made mine from MDF with wooden curtain rod ends (I got for 50 cents each!) as the feet. The base is two rectangles of MDF glued and nailed together. I make one slightly smaller than the other and use a quarter round molding in the corner between the two pieces to give the base a nice appearance. In the middle of the base is a rectangular cutout which is where the main drive pulleys sit. The pulleys are attached to a shaft that runs in bearings in the main supports but as they sit lower than the base of the supports you need space underneath them so they can turn freely. I did this to keep the supports as low as possible. On each end of the base is a wooden box for holding the Leyden jars. This has a top plate with a hole cut in it to allow the jar to slide in.

Wooden base and Leyden jar holder.

Attached to the back of each jar holder is a support for the collectors. This was made in the same way as the main supports using plastic cutting board and a wooden template on the router. In the front of each box is a brass terminal that pokes through the box. On the inside of the box there is a piece of springy brass which contacts the outside of the jar when it is inserted.

Leyden jar and collector detail.

The terminals on the front of each Leyden jar holder can be connected together wiring the jars into the circuit of the machine. This allows the charge to be collected giving you much bigger and stronger (and more dangerous) sparks. I used wires with banana plugs on each end to connect each jar to a central terminal plate that sits under the handle of the machine. This central terminal is simply a brass plate with two brass banana terminals attached to it. The wires are coiled for appearance.

Terminal plate for connecting the Leyden jars.

The  collectors are what pick up the charge from the spinning discs. I used brass doorknobs as my collectors and these form the central point where the combs, the main terminals and the connection to the Leyden jars are made. The brass doorknobs are arranged to sit directly above the center of the Leyden jars and also in line with the center of the main discs. There is a hole through them vertically through which the main terminals rods slide. The main terminal rods are 6mm aluminium rod that are bent in a curve over the top of the main discs. On the ends are brass terminals which I will describe later.

I used a piece of aluminium tube between the base of the collector and the base of the Leyden jar. A small O-ring between the collector and the aluminium tube ensure that there is a little tension between the collector and the base of the jar ensuring good electrical contact. Just beneath the collector the aluminium tube has a threaded hole into which a plastic adjusting handle screws. The handle, when screwed in tight, attaches the tube to the main terminal rod. By rotating the handles you adjust the spacing of the main terminals. The O-ring between the tube and the collector also ensures the rods don’t rotate too easily and move out of position. The handles are simply plastic tube with a brass screw epoxied to one end and a plastic ball (from a roll on deodorant bottle) hot glued to the other to finish them off.

Coming off the side of the collector terminal are the main combs. I made these from welding wire bent into a U shape. The ends and intersection of the wires are terminated in lead balls (fishing sinkers) soldered in place. This is to hide any sharp points that will leak off charge. The actual collectors I made from aluminium tape which has a series of points cut into the edges that face the main discs. I used pinking shears to cut the points. Both the wires and the aluminium tape can be easily bent to allow the combs to be positioned close to, but not touching, the main discs. If the run-out on the discs was properly adjusted the gap between the combs and the discs should remain fairly constant as the machine turns.

Collectors.

The main terminals are covered in plastic tubing to insulate them and to make them look better on the machine. The terminals on the ends are made from more brass doorknobs. I cut off part of the base to make a sphere with a hole in it.

Brass terminals.

To cover the hole in the sphere I soldered a nut to a small, circular piece of brass which was in turned soldered to the sphere. This gives me a brass terminal with a screw thread in the base. The ends of the aluminium terminal rods were threaded so the brass terminals can be screwed on.

Threaded fitting on terminals.

The image above shows the terminal being soldered up. After soldering the terminal was sanded smooth. The nut seen here was removed as it is just used to hold everything in place during soldering. The nut that the rod screws into is on the inside of the terminal.

The next component of the machine is the main driving shaft, hubs and handle. I made the hubs from more breadboard cut into circular discs using the router on a small jig again. The discs were then trued up and a driving belt groove cut into the edge on the lathe.

Cutting the driving hubs on the router.

Two hubs are made, one to drive each main disc, and they both mount to the same shaft. Drive belts link these hibs to the main disc hubs. To get the discs rotating in opposite directions you simply cross over one of the drive belts. The belts themselves I made from plastic polycord belts. This is a stretchy, circular profile plastic that can be cut to length then the ends welded together using a small flame. I got mine from a company that sells it as replacement belts for wool spinning machines.

To attach the discs to the main shaft I used small brass rods bent into an L shape that press through holes in the main shaft and into holes on the driving hubs.

Main driving hubs and shaft.

The crank handle was made from a piece of steel cut into an appropriate shape and drilled. This was welded to the main shaft. A handle was made from a replacement wooden file handle from the hardware shop drilled through it’s length. A coach bolts goes through the handle and attaches it to the crank. The wooden handle is free to rotate as you turn the machine. The whole assemble runs in skateboard bearings that sit in the base of the main uprights. The bearings are held in place by large fender washers that hold them in position inside the uprights. A brass spacer tube sets the position of the shaft at the front of the machine and an acorn nut holds it in position at the back.

The driving handle and bearings.

The final part of the machine is the neutraliser bars. These bars run across the face of each main disc, one on the front of the machine and one behind. Their purpose is to neutralise the charge across the discs and their positioning in relation to the direction of rotation and the collector combs is crucial (as in which sector they must go) to the function of the machine although their exact position (as in the angle in the sector) needs to be experimented with.

I made mine from plastic hubs turned up on the lathe. These are attached to the same shaft the main discs rotate around. The arms are made from brass rod bent into an L shape. These push into holes in the edges of the plastic hubs. The short, bent end of the L is arranged to hold a small copper brush that wipes against the sectors on the main discs.

Neutraliser hubs.

To connect the two sides of the arms I used a piece of wire and two alligator clips. I simply coiled the wire for appearance sake and actually the wire isn’t needed as the machine seems to work well enough without it. I think there is enough leakage between the ends of the arms pressed into the hubs and the steel axle shaft for the machine to work.

At the brush ends of the arms I soldered short lengths of brass tube. Into these I insert the brushes. This took a little bit of experimenting as the brushes need to touch each sector as it passes but you don’t want them putting too much pressure on the discs making them harder to turn.

Brush and brush holder.

The actual brushes I make from single core shielded audio cable. I cut an appropriate length and strip both ends. I then cut out the central core. At one end of the brush I bend the wires back 180 degrees. This end is inserted into the tube on the end of the arm. There is enough friction here to hold the brush in place and also to ensure a good electrical contact. The other end of the brush I simply fan out the wires and it is these that touch the sectors as the pass.

Brush.

The arms of the neutraliser can be rotated slightly to allow the brush to be positioned so that it just wipes the sectors. A slight angle on the arms also prevents them from vibrating as the sectors pass beneath them. You do need to replace the brushes from time to time.I think the small step each brush must make over the edges of the foil tape sectors causes a slight bending of the copper wires in the brush. Eventually the wires will work harden (copper is prone to do this) and then they break off. I often find small pieces of broken brush on the base of the machine. You only need one strand to be making contact though for the machine to work. The brushes will mark both the copper foils and the acrylic discs over time. Some people have attached small dome terminals to their sectors so the brushes only touch them and not scrape the acrylic. I don’t mind the scraped look as it makes the machine look old and used to me!

One final but very important addition that isn’t part of the machine itself is a discharge rod. The Leyden jars are simple capacitors that store charge. They can hold a charge for a very long time and are actually quite dangerous. Even though the capicatence is low (around 1nF) the voltage in them is high. To make sure the machine is safe to touch you should ALWAYS discharge the jars. To do this I made a discharge rod. This is a piece of brass rod bent into a U shape with two small steel bearings (rescued from empty spray paint cans) soldered onto the ends. This rod is attached to a length of insulating PVC pipe. I always discharge the jars before touching the machine by shorting our each jar (usually with a large spark and crack) and shorting between the main terminals.

Discharge rod.

All of the pictures above were taken as I built the machine and when I first had it working. I finally got around to painting it and also making a few small changes. I increased the diameter of the main driving hubs to be as large as possible. The bigger these are in relation to the small driving hubs the faster the discs spin. The speed of the discs affects how quickly the charge can be built up. I made new neutraliser hubs using black plastic to better match the rest of the machine. Also, in a fit of maker vanity, I had the small terminal plate engraved with my name and date for posterity. One change I would like to make is getting fabric covered wires for the machine.

Now finished the machine works very well. The largest size sparks I can get from it are about 150mm long. This is with the jars attached to the circuit. This being a static electricity generating machine it’s performance depends a lot on the weather. If the humidity is too high you get a lot of leakage off the machine and it can’t built up as high a charge.

When operating well you can hear the charge building up in the machine as soon as the handle is turned. The room fills with the small of ozone and the hairs stand up on the backs of your hand. Close to the machine you can feel a prickly wind coming off it and if you run it in a totally darkened room you get a nice corona glow from various parts of it. With the Leyden jars attached and the humidity low the resulting arcs are very strong and loud. You need to wear hearing protection to avoid damaging your hearing from the crack of the discharge! I imagine there is a lot of UV emitted from the arc too.

There are some YouTube videos of the machine running available here. The first was the unfinished machine generating 150mm long sparks on a particularly dry day.

http://www.youtube.com/watch?v=viRWICVEHCk&feature=related

Other videos are available if you look at my other videos on YouTube.

Below are pictures of the finished machine which  hopefully make some of the details in the text clearer.

My 7×12 mini lathe.

This is one of the cheap, Chinese mini lathes. The 7X12 means it has a 7 inch swing and 12 inch length. These little lathes are quite crudely made but with a little work they can be made to perform quiet well. They are easily good enough for the generally imprecise things I am making. They do require some fiddling to get them working nicely and there are various modification you can do to make them easier and nicer to use. I have done two so far.

I won’t go into too many details. If you search Google for Mini Lathe you will find some very good sites with far more information that I can post here.  I got the ideas for these two modification off sites such as these. The first is an apron chip guard I found at www.mini-lathe.com

The apron on the mini lathe is completely open at the back meaning chips and swarf can get in between the two gears used to move the carriage along the bed. I did what a lot of others have done and made a plastic cover from 3mm thick acrylic scrap I had laying about. I drilled the hole for the large gears shaft to poke through first. I enlarged it by hand with a tapered reamer until it was a close fit. I then put the plate in position, traced around the outline of the apron and cut the acrylic to size. Next I drilled and tapped three holes to take 3mm screws to hold the plate in place. I did find with the plate screwed down the little wheel was held down by it as this gear protrudes ever so slightly from the apron. I used three small brass washers to allow the plate to stand off slightly. This of course leaves a gap around the edge of the plate which is no good. To fill the gap I simply ran a bead of hot glue around the edge of the acrylic and then screwed it in place. The glue filled the gap nicely even though it doesn’t actually hold anything in place. All the oil on the apron means the glue won’t actually stick to it.

Apron chip guard.

The second modification is  much more complicated. The mini lathe arrives with only a simple nut and plate to lock the tail stock in place.You undo the nut, slide the tail stock into position then tighten the nut using a spanner. This is a major pain in the neck especially since the tail stock doesn’t have a great deal of extension in it. If you want to drill a deep hole you must position the tail stock, drill to the end of the extension, retract the drill, loosen the tail stock, slide it closer and then repeat it all over again.

I found a nice design at http://www.gadgetbuilder.com for a cam lock. Big lathe usually have this feature. It is a lever on the tail stock you use to lock and unlock the tail stock to the bed. It makes reposition it much easier and makes the lathe a hell of a lot easier to use.

Extensive details are available from the site above. The dimensions are not critical so I winged it as I went along and used whatever scrap bits I could find (leftover MGB bolts as it turned out!).  First I made up all the parts. There are three main parts that need machining. Of course you use the lathe to make up the parts to fix the lathe!

Cam lock parts.

First, on the left, there is the cam and handle. In this design this passes through a hole you drill in the back of the tail stock. I machined the cam from an old bolt and the handle is just a length of steel I had in the scrap bin. I believe it is an old motor shaft! I brazed the handle to the cam so there is no chance of this coming loose! Next to the cam is the main bolt that passed down to under the bed. To the right of that are the thimble and nut. I had to machine the nut thinner so it would clear the supports under the lathe bed.The steel plate is just some scrap 3mm steel I had lying about.

Parts assembled.

This shows the parts in their assembled position outside the tail stock so you can see how they fit together. Basically how it works is the cam passes though both the thimble and the bolt. As you turn the cam the bolt will ride up and down on the cam profile. This changes the length of the entire assembly. On the lathe you set it up so that at the maximum length the tail stock is free to slide upon the bed. As you turn the cam and shorten the entire assembly this brings the lower plate up and into contact with the bottom of the bed clamping the tail stock into position. You only need a quarter of a turn or so to do this.

To get the whole assembly to sit square I did have to mill the base of the tail stock (the casting of it is very rough) so that the thimble is level. I also drilled the hole that the cam passes though. I somehow managed to get this a little off centre but luckily the bolt is much smaller than the hole in the base of the tail stock so there is plenty of room for error here.

Milled tail stock base.

Everything is assembled on the tail stock which is then slid into place on the bed. I used some blue Loctite on the nut that holds the locking plate in place and carefully adjusted the nut so that the tail stock is firmly locked in place with the handle vertical. You turn the handle a quarter turn clockwise to unlock it (it actually needs very little turn to unlock). I made the handle short enough so it doesn’t interfere with the locking level on top of the tail stock.To stop it rotating down past 90 degrees I drilled and tapped for a 3mm screw. I didn’t have a long enough screw to make a stop so I am temporarily using a short screw with a length of plastic hose pushed over it.This works quite nicely as you can then easily push the lever to the unlocked position and it just drops silently out of the way against the plastic hose.

Handle and stop.

I used bearing grease on the assembly before installing it and then used a small circlip to hold the cam in position once everything was in place. It is all bare steel finish but everything on the lathe is oiled and greased regularly so there is little chance of it rusting.

Now I need to start making things on the lathe rather than making things for the lathe!

The A Team is a show I remember very fondly from my childhood. I was 10 and on a trip to the UK to visit my Grandmother and I distinctly remember watching an episode of The A Team when I was there. I could always remember details of it vividly and I also remember returning to NZ and being thrilled when The A Team finally came on TV here too. When you’re a 10 year old lad TV really doesn’t get any better than The A Team.

Fast forward to now, 25 year later.  Recently I rediscovered this programme and have been watching them all over again, right from the start. From the first episode where Face wasn’t played by Dirk Benedict to where I am currently up to in season 4, the ‘Cowboy George’ episode (yes, Boy George really was in an episode of The A Team). I decided that this was a good time to pause and reflect and create this little device as a tribute to this wonderful show. After re-watching all the episodes (the one I remembered from all those years ago turned out to be the second one) I seriously now can’t go out to my garage to work on projects and weld without The A Team theme playing inside my head!

I find even now, as an adult, I still get the same enjoyment and pleasure watching these episodes. Sure they are cheesy, over the top, sexist, violent and generally not what you can consider quality drama but I love them! According to Wikipedia a review at the time said “The show is made for the average 10-year-old intellect which presumably has a desire for lots of car chases, flying bullets and punch-ups.” I am happy to say I still retain some of my 10 year old intellect! Virtual web mistress would be proud (she once told me I am very much in touch with my inner child). In a recent conversation with a work colleague, who said I really must try to make it up to our LA office one day, I told her I already have a plan of things to do if I ever do make it up there. It’s a simple, two step plan:

1. Visit Disneyland (something I also did when I was 10)
2. Hire The A Team

Since a trip to the US isn’t likely anytime soon I have instead amused myself creating this little device. My A Team music box.

The first music box used a now obsolete voice recording chip. For this new box I have used a HK828 voice recorder/playback IC made by Honsitak. This neat little chip is a complete voice recorder/playback device on one IC with a minimal number of external components required. Amazingly it is even available locally from Jaycar Electronics cat. number ZZ8200.

This little chip allows you to record audio and play it back directly from the chip with no external amplifier. It will run happily on 6 volts meaning it can be battery powered and you can feed an audio signal (in my case my PC headphone output) straight into it via a de-coupling capacitor. It has several modes of operation and by changing one resistor you can vary the sample rate (hence the recording time) from around 30 to 60 seconds. The longer the recording time the lower the quality.

In my music box I used a 22K oscillator resistor to give me about 35 seconds recording time. One interesting little thing I found is that if you vary this resistor while the chip is playing back the playback will speed up and slow down accordingly. Just for fun I replaced the fixed resistor with an LDR and got all kinds of amusing sounds from the thing by waving my hand over the top of the LDR!

If you examine the datasheet (available from the link above or from the Jaycar site) you will see the chip supports several modes of operation.  I am using ‘tape mode for auto rewind’ since I only ever want to record one long message. This mode simplifies the user interface for the box and I only need to have two buttons on the box. A play/stop button and a record button. Here are some pictures of the device below:

The A Team music box.

The box has two buttons on the top and a 3.5mm audio jack on the front. Also visible on the front is the back of the speaker and several small holes to let the sound out of the box.  The red push button is the play/stop button. You press this once to start playing and press it again to stop. If you don’t stop it the recording will play through to the end and then stop automatically.

To record you plug in a lead to your audio source then you press and hold both the red play and black record buttons for the duration of the recording. To stop the record button from being pressed accidentally I made a special cover for it. I took a small pilot light (Jaycar cat. no SL2622)  and bezel and pulled it apart. These little lights have a chrome bezel that passes through the panel and is secured with a nut on the back. The actual bulb holder screws into this from behind. On the front is a small green plastic cover that can also be unscrewed. I simply unscrewed the bulb holder leaving just the bezel and it’s cover. I then used a standard small push button and simply hot glued it into the bezel from behind. This creates a very nice looking recessed push button. With the little plastic cover in place it hides the switch entirely meaning you can’t accidentally press it.

Creating a recessed push button using a pilot lamp bezel.

You can see in the top pictures how everything (just) fits inside the box. I used a four AAA cell holder for the battery and the speaker is actually inserted ‘backwards’. That is it points into the box rather than out. The only way I could get everything to fit inside the small plastic box was to put the speaker in this way around and cut a hole to allow the magnet on the back of it to pass through the lid. I drilled two holes near the speaker to allow the sound out and finished them off with 5mm LED bezels and a small piece of black felt under each one.

One thing to note about these little project cases is the crappy screws they come with to hold the lid on. The screws are very long and self tap into holes in the box. It can be quite difficult to get them to screw in, especially considering the screw heads seems to be some bizarre size that a standard Philips screwdriver bit won’t fit (and no, they aren’t Pozi-drive either). Once you do get the screws in properly you need to be careful that when you remove and replace them later you start the screw in the same thread that is already there. With plastic boxes and metal screws it is easy to end up cutting a new thread into the box which will eventually end up wearing out leaving no thread at all. And none of us likes to have loose screws! The way to avoid this is a simple little trick. When you replace the screw turn it slowly backwards first. You will hear, or more likely feel, it drop into the original thread. Then start screwing normally! This trick works for starting off any screw in it’s thread actually.

Once everything was wired up and installed in the box I simply recorded a portion of The A Team theme onto the box. Of course you can record anything you like into it easily.

Here is a little film of the finished box in action!

Yes, I know the recording finishes rather abruptly but that’s the problem with only a 30 odd second record time! Still, for most people the novelty has worn off before they reach the end anyway!

Any 10 year old will love it though