July 31, 2007

How-To: Fotosis No. 000 Schematic...

I've decided to post a schematic for an optical theremin / synth that is a simplified version of our first creation, Fotosis No. 001. Its based around the XR2206 function generator which produces the sound (Sine Wave) and the 40106 chip that I use to trigger the LDR switching function on the XR2206. The controls are simple, three pots and three toggle switches. The pots control volume, sine wave intensity and LDR switching speed and the toggles turn LDR switching on / off (S1), (S2) for high and low pitch setting and (S3) which gives you the capability of redirecting the timing resistor pins on the XR2206 chip to some other form of resistance.

You could build a hybrid sequencer / optical theremin using a micro-controller like the Arduino board with a few opto-couplers switching the timing pins through resistors (4N37's work well) or make a noise maker using the spare Hex Schmitt Triggers on the 40106. There are many possibilities. All of the Capacitors are 1uf ceramic (Farnell part number 110-0420) except C4 which is 0.33uf polyester (Farnell part number 116-6040) all resistors are 1/4 Watt. The LDRs are 1M Ohm in total darkness and the whole circuit runs on 9V dc.

A .PDF of the same schematic can be found here.

Here is a more complicated version we built and sold a few weeks ago, the link includes a video so you can get an idea of what sounds you can expect.

Any questions I will answer to the best of my abilities...


Anonymous said...

Instead of a LDR you could use an optical distance sensor:
GP2Y0A21YK from Sharp.

Only USD 10.00 - but I paid a lot more (depends where you can source it).

The output is a voltage, so you might add a transistor ciruit for the XR2206.


wedidit said...

Yeah I thought about doing that using a Sharp GP2D12 Infra-red proximity sensor (Again a voltage output between 0.2 and 3.0volts) but they retail for about 14 Euro on Farnell. I tried a similar thing by making a potential divider using an LDR and a resistor and the results were not as linear as I wanted so I stuck with the LDRs because you could interact with light emitting devices, which is lots of fun.

Anonymous said...

I congratulate, what words..., a remarkable idea