Taipan! on the Arduino(s). Part 7 (bloody hell, when will it end).

July 19th, 2012

Right, still going on this ‘little’ project. I modified the book to take an inset wooden front panel cut from some thin ply. I carefully cut a lip in the top face of the book for this to sit in so it is flush with the pages.

IMG_2598_1 IMG_2599_1 Front panel.

I also decided the original keypad would look terrible so I set about making my own. I made my own key matrix using strip board and some small switches. I also added all the resistors for the voltage divider so this keypad would need only three wires, positive, ground and the analogue output.

IMG_2605_1 Keypad.

To make the buttons I went to my favourite on-line jewellery supply place – Beadaholic. Jewellery and bead places are full of fascinating and useful things! From there I got some small copper settings and some clear glue called Diamond Glaze. My plan was to print out labels and glue them inside the copper to make buttons similar to old fashioned typewriter keys.

I printed out some suitable labels on my laser printer then used a trick from childhood when we used to make ye olde treasure maps. To make paper look old you soak it in cold tea. I left the pages overnight in the sink with some tea bags in water (Earl Grey of course). This makes the pages yellow and look old. After a night soaking I took the pages out, rinsed them off then left them to dry for the day.

IMG_2616_1 Ageing paper in tea.

I actually muffed the first lot of labels and wasn’t able to make all the keys I need so I am currently making a second lot. To make labels to fit into the little copper settings I found a piece of brass tubing the right diameter and using my small lathe turned one end to be square. I then machined a taper to provide a cutting edge. I simply used this as a punch to hand press small disc labels out of the paper. I used a piece of leather under the paper to cut into.


Punching out round labels with brass tubing.

IMG_2607_1 IMG_2613_1

After punching out the labels I glued them into the copper settings using the diamond glaze. I built up a nice, thick coat. It looks milky when wet but it dries totally clear.

To hold the newly made buttons in place over the buttons I cut and drilled an aluminium plate. The plate is the same size as the keypad circuit board. A second circuit board will contain the two microprocessor chips as well as the small piezo buzzer and flash memory. The whole lot will be assembled as a stack with suitable screws and spacers. I need to get a female socket (like on the Arduino board itself) to go on the main board so the keypad board can plug into it. The whole lot will go inside the book under the wooden front panel.

I need to make the remaining keys but I temporarily mocked it up to see how it will look. To actually keep the keys in place I will either glue them directly to the push buttons with a small drop of superglue or else I will glue them to strips of ribbon running under the aluminium over the tops of the keys. It also occurred to me I could have soldered them to strips of flexible copper de-soldering braid but I would have had to do that before gluing in the labels. Now the heat would ruin them.

IMG_2618_1 IMG_2620_1 IMG_2621_1

The keys look very good. They have a nice aged effect. The aluminium will need some sort of ageing or coating since it looks wrong and too modern now. Perhaps some suitable paper glued over the top will look fine. With the keypad and main board in one unit I should just have room for everything in the book, including eight AA rechargeable batteries to provide power.

I might use the same technique I used to make the keys to make some more cufflinks. A cufflink base can be soldered to the copper setting then any picture, old stamps, labels, whatever can be cut out and set into the copper using the diamond glaze. That’s a project for another day.

I have finished tidying up the code but still want to do more testing (well I actually AM a tester). I had one nasty bug it took me ages to work out. Turned out to be a character buffer one byte too short in one particular circumstance. The buffer overflow caused all kinds of weirdness!

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