Adventures in Circuit Bending: Vtech Tiny Touch phone

Last evening I embarked on a circuit-bending project, and this forum provides me a unique opportunity to document the experience.

For those who are not familiar with circuit bending, it basically the process of modifying the electronics in existing audio devices, usually simple analog circuits in musical toys. In the process, one can add new expressive controls to create a unique, albiet “lo fi”, instrument. A great introduction on circuit bending can be found at Reed Ghazala's Art of Circuit Bending. Additionally the blog Get LoFi has a wealth of information and circuit bending projects and instruments.

This experiment involves the Vtech Tiny Touch phone. It plays a few simple phrases relating to numbers and colors as the buttons on the phone are pressed. You can listen to an example here. Vtech toys are good circuit-bending fodder, and I've tried the phones before. During my first attempt, I shorted out the integrated circuit (oops), which ended that effort. The second time I did a simple bend across a timing circuit that allowed me to alter the speed and pitch of the sound with a potentiometer. I had this instrument open for kids to play with during the my show at Zeum in San Francisco this past spring, which turned about to be a death sentence for it. One kid happily showed his parents and me the capacitor he managed to pull off the circuit board. This time I'm going more slowly and methodically, with the goal of a more interesting and robust instrument.

First, we open up the phone to reveal its guts (i.e., circuitry):

Now grab a test wire (i.e., with clips on the ends) and start looking for interesting “bends” by shorting different points in the circuit. In general, this is a hit or miss process and experimentation is the rule of the game. However, care should be taken to avoid shorts that could damage the audio circuits. In particular, stay clear of anything that connects directly to the batteries.

A rather effective short is opposite corners of the IC board, as illustrated by the pink dots in the closeup below:

Shorting these leads, which essentially drops the resistance to near zero, slows down a timer and thus the speed and pitch of the audio, as can be heard in this audio clip. Note the slower version of the telephone ring. From this result, one can conclude that varying the resistance changes the timing and pitch of the sound, in particular highwer resistance yields higher pitch, with infinite resistance (i.e., open circuit) restoring the original behavior. Such a bend is a good opportunity for a potentiometer to mechanically change the pitch, or a photocell to use light as a pitch control. For now, I am attaching a photocell using alligator clips:


Cupping my hand over the photocell and moving it closer and further while pressing buttons yields variable-pitch sound and beginnings of a new circuit-bent instrument.

I could stop here and make this bend permanent, but I would to continue with other options, including switching between photo, mechanical, and null modulation, as well routing other signals over this bend to create FM synthesis. I will continue to document this project here as I find more time to work on it.

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