Introduction:
Want to give circuit bending a go on the cheap? Don’t want to breaking a Speak N’ Spell first time out? Dollar stores are a great source for musical toys to mess with. This is an attempt at a step-by-step guide to a simple bend typical of what you can do.
Made in China goodness for 100 Canadian pennies, batteries not included. There is no on/off switch, it plays notes when the switch is down, little songs when it is up. This purple one was picked up at a place called Dollarama. Your mileage may very but for a buck, you don’t have much to lose.
Parts and Tools:
Optional parts and tools are needed to make your bend permanent, if you just want to mess around you don’t need to bother with them.
Parts:
A Musical Piano Toy Musical Jouet
A 1MΩ Potentiometer. Anything from 300kΩ up will likely produce neat results.
Optional Parts:
Two pieces of small wire, about 2″ long. More flexible is better.
Tools:
Two small alligator clips ($9 for 10 at The Source/Radio Shack catalog #2781156)
A small phillips screwdriver
Optional Tools:
A drill with a drill bit the same size as your potentiometer
Soldering Iron & Solder
Potentiometers: WTF?
A potentiometer is a variable resistor. It creates a drop in voltage between the wires connected to it. They come in many shapes and sizes but are always measured in a unit called an Ohm, represented by an Omega Symbol (Ω). One ohm of resistance isn’t very much, potentiometers are typically need to provide a lot more then that. To keep the numbers of zeros manageable the letters ‘K’ or ‘M’ are used to represent 1000s(K) or 1,000,000s(M) of Ohms. The 1 Meg potentiometer being used here provides about 1,000,000 Ohms of resistance (a fair bit) when turned one way, and about 0 Ohms (direct connection) when turned the other.
Potentiometers generally have three connection points. We’re only going to need two.
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 This style is also common. |
You can buy potentiometers from electronics part supply places. They’re very common. Ask for a “1 Meg Linear taper potentiometer” and buy it if you like the way it looks. $3 is the most you should pay. The Source/Radio Shack sells them for that much, catalog #2710211. The store will likely also sell plastic knobs to fit on top if you desire.
Appearances will vary, but you want a little thing with a rotating shaft and three connectors.
Piano Disassembly:
First pop in some AA batteries in and make sure it works. You can leave the batteries in for this whole operation.
Remove four screws from the back and carefully open the case. The wires inside aren’t very strong and break off easily. You can fix them fairly quickly with a soldering iron but it’s extra hassle.
The Bend:
What we want to do is connect the potentiometer into the pianos circuit. There are lots of places we could do it that might provide different effects. To find a good one we’ll use the alligator clips.
Connect one side of each of alligator clips to two of the potentiometers connectors. One to the middle connector, one to the left or right (doesn’t matter which).
Turn the potentiometer to about the middle position.
Now use the other side the your two alligator clips to connect to the various exposed pads on the pianos circuit board. Play around. Try to avoid wires connected to the batteries, if you get smoke, a spark or smell burning plastic, it’s best to back off.
Ah-ha, found two good connection points. They seem to affect the pitch and just cut the audio all together when directly connected. Perfect.
Connect up your clips, turn your potentiometer, pow, you’re circuit bending.
Permanent Install: The optional part
If you want to close things you’ll need to do some soldering. There are lots of good tutorial on the web but in the end its a matter of practice. Get some decent solder and a low wattage soldering iron and give it a go.First, find a spot on your keyboard to mount your potentiometer. It can be surprisingly tight inside these toys, it took me two tries to drill it right.
Now solder wires from the points on the pianos circuit board over to the connectors on the potentiometer. You want to make the same connections that alligator clips provided before.
Put the case back together, careful of breaking wires, put the screws back in, done.
Tags: bending, electronics, music