Tuesday, 3 February 2015

CGS 86 - Build notes for the Serge Touch Keyboard

Firstly, I'd like to thank Ken Stone of Cat Girl Synths for making this kit possible.
You can find his build instructions here:

Useful Links:
1. Muffwiggler Thread
2. That famous Synapse Article by Arpad Benares (care of Cyndustries)
3. PAiA - Touch switches (like those used on their Programable Drum Set)

I'm currently waiting for some pots to arrive for the TKB build.
The Serge TKB also uses a touch keyboard and it seems logical to build the CGS 86 at the same time.
I think these two projects share many common concepts. If I understand this correctly, both use the capacitance principle (not FSR - force sensing resistors).

It looks like the two BC547 transistors on the small driver PCB make up the emitter coupled astable oscillator (Multivibrator circuit). They produce that famous square wave of 100khz. 

The second larger PCB is called the detector since it detects when the output of the astable osc changes. When you touch a key, some of that square wave is shunted to ground and the Op Amp's (The LM3900's) output goes +ve in response.

I'm hoping the CGS 86 will compliment the TKB. Possibly, I'll instal them in the same boat.

Here are the virgin PCBs:

You will need two of the larger green PCBs if you wish to use all 16 touch plates.

IC headers, Resistors, Diodes first.

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