Last week-end I have bought five noise-making plastic toys at a yard sale in Paris; I then ordered knobs and switches from ebay and from a local electronic store. What for? For the purpose of circuit bending of course!
Out of the four toys, one was already non working when trying with new batteries. Once opened, there was nothing visibly wrong, every wire connected. Whatever what we do with it, only noise comes out from the two speakers.
I searched how to start the art of circuit bending (I have been taught electronics in the academic fashion in engineering school, but I suspected circuit bending was somewhat different: usually in a lab, you do your best to avoid short circuits, at all costs!
I therefore read (but too quickly) the introduction by Reed Ghazala before opening the second toy. Then I started to short circuit each pin to each other while triggering the noises. After a few minutes, I believed I had found an interesting connection (as the sound was getting slightly strange) but immediately after, no more noise. I killed the toy.
Now I understand that having the sound slightly strange is precisely what we need to avoid. It was written in the guide…
Looking further I discovered additional advices (use only the body resistance to start connecting pins together, use a voltmeter to mark every high tension on the circuit to avoid them later).
Then it was quick since the circuit is so simple. I added a mini Jack output and checked it with headphones. I also added a switch on the output in order to interrupt the sound, and another (UPDATE) on the batteries wires to be able to shut down very quickly, just in case…
With only 4 resistors on the circuit it was easy to bypass them with my body resistance, and R2 is obviously controlling the pitch. So happy, this is really that simple. R2 is 100K?, so now I must test bypassing it with a potentiometer to find out the right value range to use. As it is all SMC (surface mount component) there will be some sport.
UPDATE I removed the 100K? SMC resistor that controls the pitch and replaced it with a 470K? potentiometer plus a serial 10k? resistor plus a serial switch to pause the playback (playback goes on where it was when switching back on, since the pause switch actually stops the clock to the chip).
The most difficult part was actually to put everything into the small box, without breaking anything.
It is a very simple circuit bending since only the pitch is controlled here.
Here is a demo video on Vimeo: