Gemmy skulls are great for hacking. Their jaws move, their eyes light up (and even move on some models), and best of all they’re cheap.

Right out of the box they’re not so impressive though. You trip the motion sensor and garbled noise comes out of the tiny speaker for a few seconds.

What’s it saying? It sounds kind of like “I’m on sale” to me. I guess they just want you to subconsciously decode the message and buy more skulls.

The best thing to do with these skulls is to rip their brains out and add MIDI control so you can sync them with your own soundtrack. This tutorial will show you how to do just that.

What You Need

• 1 Gemmy Animated Scary Skull
• 1 MIDI to active-high logic-level board (I used Midify but others would work too)
• 1 Small perfboard
• 1 TIP120 NPN Darlington Transistor
• 1 2N2222 NPN Transistor
• 2 1k resistors
• 2 4.7k resistors
• 1 47 ohm resistor (link goes to ½-watt but ¼-watt is fine)
• 1 1N4004 Diode
• 1 10uf Electrolytic Capacitor (link is to non-polarized but doesn’t have to be)
• Wire
• Wire cutters
• Wire stripper
• Soldering stuff
• Phillips Screwdriver
• Hot-glue gun

Build the MIDI Control Circuit

The circuit is based around the Division 6 Midify board, which basically looks for MIDI note on/off commands and turns on/off the corresponding outputs. Since the Midify board can’t supply much current we need to add some transistors to do the heavy lifting.

Note: there are several other MIDI boards out there that will work too, but this one is very small and easy to fit inside the skull.

Another note: The Midify board has 12 outputs, so you could run up to 6 skulls from one board (or 12 if you only use the mouth, for instance).

Here is what you need to build:

You only need ½ of the perfboard, so snap it in half and save the other part for something else.

Start by hot-gluing the Midify board to the edge of the perfboard.

Next, use a blob of solder to short the two pads on the board marked “high”. This will put Midify in active-high mode, meaning that when an output is “on” it will be high and when it is “off” it will be hi-z.

Stuff all your parts so you know that your layout works and that you have room for everything.

Start soldering. You may want to attach wire “pigtails” for power and the motor and LED outputs so that it’s easier to connect later. Here’s what my finished board looked like:

Note: I’m running two skulls from my board so it has twice as many parts as you need for just one. If you want to run multiple skulls it’s easy to add transistor circuits to the Midify outputs. The 2N2222 circuit with the 47-ohm current limiting resistor is for the eyes and the TIP120 circuit with the snubber diode is for the mouth.

Braaaaaaains!

Now that the circuit is ready to be installed it’s time to disassemble the skull. There are four screws on the back that need to be removed.

Pull the two halves of the skull apart.

Clip all the wires going to the circuit board. Clip them close to the board so you have some wire to work with when you hook up other stuff later.

Remove the circuit board.

Remove the speaker, transducer, and whatever else you don’t plan on using. Add them to your “free parts” bin.

The Transplant

At this point you have a few choices to make. First, where to get power. You can continue to use the built-in batteries, or you can power everything with an external 5 volt power supply. Another choice is whether or not to use the original power switch. Finally, it just so happens that the 2.5mm mono “Try Me” button jack on the bottom of the skull is the same as the one that comes with the Midify board, meaning you can either drill a new hole and mount that one or just hook up the stock jack in the bottom. From here on out I’ll assume you decided to use built-in everything.

Connect the batteries and power switch, all in series.

Connect MI4 and MI5 on the Midify board to the 2.5mm jack. Make sure MI4 goes to the tip of the connector.

Use the washer-head screws you removed earlier to attach your new circuit board to the bottom of the skull.

Solder the Motor and LED outputs of the board to the mouth and eyes of the skull. The wire colors are on the schematic to make it easier. Use tape or heat-shrink tubing to insulate the conections.

Testing
Reassemble the skull, making sure that none of the wires you added (or any of the loose ones) will interfere with the mechanics of the mouth.

Use the MIDI cable that came with the Midify board to connect the skull to a MIDI keyboard. Note: if you are using the jack in the bottom of the skull you may want to chop the 2.5mm plug off of the MIDI cable and attach the right-angle one from the “Try Me” button. Just make sure you get the polarity right.

Turn on the skull. Look for no smoke.

Press middle C on the keyboard. The mouth should open.

Press C# above middle C. The eyes should light up. (I hooked mine up different I guess, because these are backwards in the video. It doesn’t really matter what output you map to what.)

The default mode of the Midify board is mono, so you probably can’t run the eyes and the mouth at the same time. Here are instructions for changing it to poly mode.

Using Your New Skull
Now that you have a MIDI-controlled talking skull it’s up to you how you use it.

For this demo I connected the skull to my PC, which is running Sonar. First I made an audio track with the music. Then I recorded a MIDI track, using a keyboard to trigger the mouth movements to the music. Then I recorded another MIDI track for the eyes. If I messed up the timing it was pretty easy to go in and edit it in the software.

That’s it. Go forth and build your loyal skull army!

Update: Here are a couple talking skulls singing with some friends: