Making Horrible Little Toys Horrific

A pile of 2n7000 MOSFETs, great for simple voltage control!

About a year ago, I posted a video about using MOSFETS to control voltage in devices (instruments?) that were never intended to have that kind of control. I chose the 2n7000 MOSFET because it acts like a resistor in the range of voltages we usually care about in synthesizers, around 0-10V. In the second video, I added a resistor to prevent drawing too much current and blowing the transistor. But that’s not (usually) necessary for a tiny, battery-powered toy, particularly a low-voltage, low-current digital one!

A small circuit board from an obnoxious toy truck that makes sounds.
A small circuit board from an obnoxious toy truck that makes sounds. The alligator clip is connected to the Gate pin (the middle pin) of the transistor that shorts out the button that activates that sound by soldering a test point from the V+ side of the circuit to the Drain (the righthand side pin while facing the flat side) and soldering to the microcontroller input side of the circuit to the Source (the left pin).

What’s happening here is that an increase of voltage at the Gate opens up the transistor, which then shorts the switch that it’s replacing. It doesn’t open up until it reaches 0.7V, but the usual range of voltages we’d expect is up to +5. So as long as our triggering voltage is above 0.8V, it will act at least a little like the switch has been pressed. The microcontroller needs a particular voltage to register it as well, but the nice thing about this setup is that, as long as “ground” on all components is connected, this MOSFET only transmits current and voltage that this one component already expects. In that way, we can isolate components from each other.

In this case, I sent it signals from a sequencer — an instrument that sends voltage levels in sequence that often correspond to notes. In this case, though, it’s just sending on and off signals.

Chook chook chook chawhoook!

This will work for adding a gate to just about any existing switch! Here’s an even weirder toy with the same trick applied, as well as an audio out installed into the back of its head!

It has a momentary switch in its belly button that we shorted with the transistor. And now it has a really rude sense of humor.

Modular systems are a function of industrial society. But do people of The Fifth World still know how to agree to standards? With their acute interest in efficiency, I think they might have carried that lesson forward!

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