
Here is a schematic promised for a very long time. 4 Oscillator circuit based on the
4093 Quad Shmitt Trigger IC. I have used identical circuits in the
GameBoy Theremin Synth and the
Atari Joystick Synth. There is not much to creating an oscillator. In this case 1uF electrolytic capacitors was placed between the input pin and the ground. Also the Optical resistor from the output pin of each individual gate back to the same input pin as the cap, this creates the feedback

needed for oscillation. For this project a 0k to 200k photoresistor worked fairly well, 0 to 15k would work but not as many low frequencies, more upper range, this can be countered with a 10uf cap of needed. The signals from each oscillator are mixed by diodes in the direction of the output. If this is not there and the outputs are just soldered together, the circuit will not work. This solution has huge limitations and drawbacks, because certain frequencies are louder then others. An optimal solution is to use a Quad Op-amp to do the mixing. This IC will run on a 9Volt battery with all the ground connections made to the Vss Pin 7. The +9 goes to the Vdd pin 14. The schematic assumes proper power applied to the IC. The free input pins can be used for touch controls and or inputs from the other oscillators. Once each individual oscillator is built, various output to input combinations can be tried. Good luck and let me know if I messed something up.
7 Comments:
At 2/23/2006 08:01:18 AM, boo said…
:-) Thank you!
At 2/24/2006 01:39:49 AM, Evil Paul said…
Yay! Thanks mate. I will send pics when I build one.
At 2/25/2006 09:23:57 PM, Anonymous said…
http://www.doctronics.co.uk/gt_3.htm
few more tips,like switching it off...gated astable.
At 6/30/2006 12:20:49 PM, Anonymous said…
Hey... I was wondering what kinds of diodes ur using and if you could point me to a scheme for the op-amp substitution you suggested here.
Thanks
At 6/30/2006 12:41:46 PM, Master said…
The diodes were 1N94? something or other. I think. Any low voltage diode will work, even a LED would imagine. The op-amp circuit would be like a buffering circuit. Where you take the output of the op-amp and feed it right back to the input pin, without a resistor. Sorry for being a little vague, but take a look at the schematic on this page
http://ourworld.compuserve.com/homepages/Bill_Bowden/opamp.htm
Its the "voltage follower" one. Hope this helps.
At 7/12/2006 03:03:11 PM, Anonymous said…
for the Schematic you showed, according to the pinout, does that mean you connect the photocels to pins 1 & 3, 4 & 5, 11 & 12, 10 & 8?
Also-
If you use pots, which pins connect to the middle tab? 3,4,10 and 11 or 1,5,12,8?
Thanks- Simple yet great sounding!
At 7/13/2006 03:15:52 AM, TomBugs said…
YoYo - umm, check the 40106 chip - it'll do SIX oscillators for you! Its a Hex Schmitt Trigger - fine for this application where you're only using one input of each gate.
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