Mini-Keys — A little keyboard circuit bend (part 1)

I have been working on a small but complicated project for the last week or so. Basiclly it’s a continuation of the last mini-keyboard circuit that I fried. I posted some pics in an earlier post.

The original project had a dual LFO powered by a 9V battery. I was using the 556 dual timer chip to accomplish this.

Long story shore; I fried the little guy and the 556 timer while trying to adapt the keyboard for wall power.

The new keyboard and circuit design

I was lucky in the fact that I had found almost the exact same keyboard the weekend before I fried it.

joystickStuff 005

I could just substitute it in for the old one and none would be the wiser.

The only problem was that I had fried the 556 chip and didn’t have another one. I could have gone to Radio Shack or bought some online. I didn’t really want to do either. The Shack is too expensive and ordering online takes too long. I had to come up with something else.

joystickStuff 006

I decided to practice what I preach and give the lm386 a go. So I followed the schematic on the datasheet and wired a square wave. And wouldn’t you know it… It worked.

The “square wave” seemed to act a little differently than the 555 timer square wave. It seemed to have more slope on the beginning and end of the square wave shape. I know this because I had it running an LED. The LED seemed to dim as the capacitor discharged.

Anyway, I wired up two of those lm386 oscillators and played around with them. Crossed a wire here, added a capacitor there. You know how it goes.

mini-keyboard 002

Mostly, the two LFO’s are effecting the pitch (vibrato if you will). One is directly effecting the pitch and the other one is modulating the first LFO and also operating a transistor gate which is almost acting like a tremolo.

All in all I came out with a pretty good design. One that I’m sure could be patched into just about anything with a timing resistor.

The fun stuff

The best part is the joystick. It operates the both LFO’s frequencies at the same time. LFO1 is the X-axis and LFO2 is the Y-axis.

mini-keyboard 003

The really cool thing is the second LFO. As I said, it operates a transistor gate for the first LFO. These different combinations make some really interesting modulation to the sound of the keyboard. But, it also is patched into the pitch resistor array at a different place than LFO1. So, when all is said and done, the sounds that you get are really quite diverse.

I have a switch that activates the second pitch controlling LFO2 (but not the transistor gate of LFO2) which basically gives the keyboard a super alien/insect sound. When I blast that sucker, I feel like I’m hearing ants communicate.


I have only just begun to paint this beast but so far it’s turning out pretty good.

mini-keyboard 019


mini-keyboard 013

-videos and schematics coming soon in part 2

4 thoughts on “Mini-Keys — A little keyboard circuit bend (part 1)

  1. Pingback: Insect-A-Tron – (Mini-Keys circuit bending part2) « Second Hand Synth

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