[sdiy] Calculator Synth

[Grant Richter]

4000 series CMOS is happy to run on a 9 volt battery. Make sure to use a
bypass cap across the battery voltage.

An 8 key keyboard can be encoded with a single CD4532 priority encoder. The
output will be binary, and you can put 10K,20K and 40K resistors on the
output lines to generate stepped voltages. Or you could make them pots and
then get goofy scales. This would be the simplest for a little calculator
synth, you can also cascade the 4532s to get more keys.

You could run the resistors from the output lines of the 4532 directly to
the timing cap of an astable 555. With no key pressed, you have no charging
current and no oscillation. So just a CD4532 and a 555 timer could be used
to make a little keyboard controlled organ. It would be hard to tune of
course, not a precision device but cheap and fun.

The CD4532 has a signal which can be used as a gate for a simple envelope
generator. And a Radio Shack photoresistor and LED can be used to make a VCF
and VCA.

The schematic for a bigger encoder is on the last page of

http://omega.tellus.vallentuna.se/anders/pdf/8782dwg.pdf

A little calculator synth would not need 64 keys, but you can't use a 4052
because the address lines are tied together.

It works like this: The counter counts at high speed an scans the two 4051s
looking for where they cross. At that point a strobe is generated and used
to latch that key number into a latch. The number is then turned into a
voltage by a DAC. It works with any kind of keyboard.