[sdiy] FPGA/Synth DIY thoughts

[Grant Richter]

Nick Hartl and I have experimented with capacitive keyboards done with a
single FPGA. Connect two pins together with a resisitor, and put a
touchplate one one pin. Then toggle the drive pin and time how long it takes
the other to change state. This measures the C in the RC time constant.
Touchy about temperature and humidity though (no pun intended).

The nice thing is that a MIDI transmitter is a simple matter in an FPGA if
you set the clock frequency properly. So a single FPGA and PCB could make a
polyphonic capacitive MIDI keyboard. Another immense financial bonanza just
waiting to happen <snicker>

Another thing to consider is using an FPGA like a group of 555 timers. Any
two pins with an RC time constant between can function like an oscillator,
or envelope generator. You can use the FPGA directly as an analog component
by lowpass filtering a high frequency PWM signal to generate variable
voltages.

An 88 pin PLCC could be a direct source of 88 variable voltages, envelopes
or waveforms. And a sequencer is a piece of cake....

Plus you can talk to it in schematic, text or a mixture of the two. The JTAG
download capability is just nifty for debugging.

> 
> There are many things that you can do with these that more or less
> relates to Synths, but now you can DIY at least. We can allways ask
> people to avoid tossing big lumps of code directly on the list, there
> are web-servers or private-email available for that, but other than
> that I think that the discussions could be good for many.
>