Hack the APC

APC 3Some examples of fun things to do

Since the APC is a simple circuit that uses a dual timer, there are tons of ways to hack it. You can do anything from changing the variable resistor to add strange controls, adding lights as outputs, or even make it trigger from external input. You can even use the basic circuit to PWM an LED, or build a simple dual LFO. By cutting a trace and adding a wire, the possibilities become endless. Just about anything you do changes the sound as well, which can be really fun.

Eventually this page will be filled out with a variety of specific hacks, and how to do them. For them moment I am going to cover some of the fun things I’ve done with my APCs. Eventually there will be a way for people to submit fun things they’ve done with their own APCs. For now it will just be a few of the ones I have built.

The IED (Improvised Electronic Device)


This is probably my favorite APC of them all. I grabbed a case from Radioshack for $3, and it fit all of the components in perfectly. I replaced the right potentiometer for a simple photo resistor (Jameco has a decent selection for a good price), which has created a fairly simple photo theremin. The other pot could have been replaced with just a simple resistor, but I wanted some additional controls. I actually wish that I hadn’t installed the switch, as I almost exclusively play this with the button, so it just gets in the way. This is the one I hand over to people and have to actually ask for it back.

APC KIT 71APC KIT 72The inside is an extremely tight fit, but it works. Since the case is plastic I didn’t have to worry about things shorting. There is also just enough room for the PCB to fit under the battery. The solid core wires hold everything tightly in place, and even without adhesives everything stays in place when the case is shaken around. The photo resistor is the most interesting thing to add into the APC for me.

The Holiday Tin

APC KIT 73This is a tin I picked up at a Goodwill for $0.50, scratches included! I added in two photo resistors in line with a switch (connected to the “Touch” points on the PCB), so I can choose to use either the knobs, or the photo resistors. I also use a rocker switch for power, which was a good choice for this case. The button is actually seldom used, as the controls become too difficult to manipulate with the knobs on the side. I set the pots so that they increase in frequency when turned up and towards the front of the tin. I also replaced the pots with 25mm ones instead of the 17mm ones included in the kit. The larger ones have a slightly smoother and easier movement, which is great for larger knobs.

APC KIT 74On the “front” of the APC is the output jack and a dual color red/blue LED. I have the first output running into red (pin 5), and the second running into blue (pin 9), so you get a shift in color as the frequency changes for each oscillator. The first LED was burned out because I didn’t put in the proper resistor, so make sure to calculate on 9V as the source, don’t be stingy.

APC KIT 75With the twisted solid core wire, it holds up surprisingly well in an open format. You can also see the 30AWG wirewrap wire I’m using for the LED, which I have braided. The 9V I will sometimes tape down, as it is the only part that will really come loose when the case is shaken.

The Oomlout


I met Oomlout at Maker Faire UK09, and traded an early APC kit for one of their laser cut cases. It already had two spots for a potentiometer and a button, so how perfect was that! I added in some RGB slow blinking LEDs that come one when you flip the switch to the left. This one is only controllable through the red button in the middle, and it’s a ton of fun due to that limit. I also added in a rather terrible photo resistor, which only works in fairly dark environments, and only then if the LEDs are not going. This should be a lesson to pick a photo resistor only when you are in a fairly normal lighting condition, and not in a dark place.


I also have an LED coming straight off the speaker since the case is clear, which is actually quite fun. It’s not nearly as bright as the other two LEDs, but it is useful to show off the actual pulses being generated.

The Nancy Reagan Special


Just say no to pots. I wanted to push this as far as I could. There are no controls on the case, just two pennies. I’m actually using the case itself as the third contact to bring the + voltage to the pennies. There is also an LED that lights up based off of the audio output. Also, it only runs on 3V.

APC KIT 79Since there was no room for a speaker, only the line out was used for this one. Since the voltage is so low, I actually wired it into the speaker position.

APC KIT 80As you can see, there is but a single coin cell for power. I’ve also used heat shrink and hot glue to keep things in place. There is still a surprising amount of room inside. I’ve also soldered a wire from the + voltage connections on the PCB to both the bottom and top of the tin. The only controls are the pennies on the top. It’s interesting as an exercise, but I wouldn’t suggest people build one themselves. It can be (not surprisingly) very difficult to control.

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