Introduction: Modify a Talking Skull to Say Anything You Want

Every Halloween, inexpensive talking skulls are available as decorations. They look good, but they have a tiny speaker inside them, making them hard to understand. And they only say a few pre-programmed things. What if you could hack one so that you could make it say anything you want? And have it work with any speakers you own?

Here's what one that I got says. Notice that I have to snap my fingers at it to get it to play. Also, he doesn't just talk - he's got his own sound effects and music as well. I think this makes him harder to understand.

Some friends and I worked out how to do this inexpensively; as a matter of fact, this is the least expensive way possible to do this. These talking skulls are usually about $20.00 new, and less off-season. Other versions of this project on the web use parts that cost lots more than the skull!

Here's a quick explanation and demo:

We made a custom-designed circuit that needs less than $5.00 of parts – plus we’ve arranged with a company to offer a professionally printed circuit board so you can assemble it like a kit, instead of working out how to build it on prototyping board. The professionally-made board is quite reasonably priced, and can be bought as a bare board where you supply the parts, as a kit with the parts, or assembled (see step 2 for details).

How it works: The circuit inside the skull is replaced by a small, custom-made board that will respond to “beeps” on an audio track; when the circuit hears a “beep” it turns on the motor in the skull, opening the mouth.

It’s a great project paired with a microcontroller (Arduino, EFX-Tek Prop-1, or Picaxe) that can trigger the playback of an MP3 or WAV file.

This is a multiple-part project, and you should have some experience in hobby electronics: Reading circuit schematics, soldering, assembling circuit boards, editing sound files on your computer, and programming a microcontroller to play back MP3s when you want.

2014 update: Someone asked if you could use this live with a microphone, so you could be hidden somewhere, and have a skull that is sitting on a table talk to people and react to what they say. Great idea! Yes, you can - there's a simple way (and it's easier than the original project!) Go to "Testing the skull" and see the notes at the bottom of the page.

Step 1: Project Overview

Here’s everything you’ll do:

1. Hack the talking skull, removing the internal circuit board and speaker, and replacing them with a connection on the outside of the skull.

2. Build a small custom circuit board that controls the skull’s motor.

3. On your computer, add beeps to one channel of a stereo audio track, to trigger the circuit board, which makes the skull talk.

4. Program a microcontroller to play back your custom mp3 when you want. The microcontroller can run a timed program, or be set up to react to a motion detector or a button. And, you’ll need some kind of mp3 playback module. There are lots of choices for mp3 playback these days. I’ll list several options at the end.

5. Connect the audio output of the custom circuit board to speakers. (An old pair of computer desktop speakers works fine for this, but you can go bigger if you need to.)

This seems like a lot of stuff, but once you’ve modified the skull, and built the circuit board, it’s pretty easy to set up a new audio track. Then you just have to play it back with your microcontroller.

Step 2: Parts Needed

Talking skull – Look in discount stores (Target, Walmart, RiteAid, CVS, etc.) during the Halloween season. Also search online for "Gemmy Talking Skull". You can also go to the Gemmy website at:

Then search for "skull" and some of the results will be talking skulls. The different versions will be carried by different retailers, and the info page for each version will show which chain store has picked it up. Since this is a novelty item, it will change in looks each year, and different stores will carry different versions. Some years it looks like the one in this Instructable, some years it looks like a pirate, some years it has a wig on, etc. etc.

Electronics components: (Also attached as an Excel file, with part numbers for Jameco and Radio Shack)

LM358P OpAmp
IC socket, 8 pin
Capacitor, disc, 0.1uF (104)
10k ohm resistor (BRN-BL-OR)
100k ohm resistor (BRN-BL-Y)
4.7k ohm resistor (Y-PUR-R)
1N4148 Diode
Slide switch mini DPDT (optional)
3.5mm stereo jack, PCB mount
9V battery snap

1/8" mono phone plug (control cable)
1/8" mono phone jack (control cable)
150 ohm resistor (BRN-GN-BRN) (LEDs)

You can order the circuit board ready-made from Blue Point Engineering at:

It's called the "Talking Skull DC Motor Controller" and can be ordered as a circuit board only (you supply the parts and assemble it), as a kit with all the parts for you to assemble, or completely assembled.

Note that this is a new company supplying the boards - the previous company closed up and passed their designs onto Blue Point. They provided me with a sample of the board, I've tested it, and it works the same.

The circuit schematic is in a later step.

Step 3: About the Skulls

The talking skulls I use in this Instructable come from a company named Gemmy Industries (, which specializes in holiday decorations. The look of the skulls varies from year to year, but they have the same insides.

There’s a small hobby motor connected to a string. When the motor is turned on, it winds up the string and pulls a lever, opening the mouth. When the motor is turned off, a spring pulls the mouth shut and unwinds the string from the motor.

As a side note, I have to say that I’m impressed with this design. Some unknown engineer figured out how to make a good talking skull inexpensively. If you take good care of them, they actually last quite a long time. On the other hand, if yours gets broken during a Halloween party, a new one is cheap.

Also, a key point of this build is that none of the custom electronics are housed in the skull. I add a mono phone jack to the back, and plug in a cable that connects to the mouth and LED eyes. This lets me put the microcontroller, MP3 board and speaker where ever I want. It also means that once you modify the skull and close it up, you never have to open it up again.

Step 4: Taking Apart the Skull

There are some screws on the back of the skull, take those out and save them. Then take off the back. Inside is a battery pack in the base, a circuit board, a small speaker, and wires going to the motor and LEDs for the eyes, as well as a detector to see motion.

We’re going to take out the circuit board and the speaker. Cut the wires as close to the circuit board as you can, and remove it and the speaker. At this point, take some time and figure out how the motor and the LED eyes are connected. In my skull, they had two white wires coming from the motor, and white and black wires coming from the LEDs. Take notes and label or mark the wires so you know which ones do what for later.

There were also two brown wires coming from the motion sensor. I took the motion sensor out – there was a blob of hot glue on it, I popped that off and clipped the wires to the sensor, and pushed the sensor out through the nose. It got tossed in my parts box for possible use in another project.

Step 5: Modifying the Skull

We only need two wires to control the skull, so I used a 1/8” mono phone jack, connected to the battery pack, on/off switch, motor, and LED eyes.

Refer to the diagram of the internal skull connections.

I drilled a small hole for the mono jack, and screwed it in place. The skull already had an on/off switch, originally used to toggle demo mode, so I use it to turn the internal batteries on & off. I unscrewed it and soldered new wires to it. The LEDs in this skull were wired together in series, so I added a 150 ohm resistor to them.

Test all this out with alligator clip wires, to understand how it all works, before you solder it up.

See the photos of the skull insides after it's been modified.

Step 6: Testing the Skull

Once you've modified the skull, it's very easy to test it all before going further. I suggest verifying you've got the right connections before soldering everything in place, by using alligator clips to make the connections, because who knows if your skull is exactly like the one I used?

Watch this video to see how to test the skull:

2014 update: If you want to use this live, instead of with a pre-recorded mp3, it's easy. Connect a button to the ends of the two wires that come out of the skull. When you press the button, the skull's mouth opens. Now the skull is an "electronic puppet" and you can animate it in real-time, to match what you're saying. Make the wires coming out of the skull long enough to go to a hiding place where you can watch people walk up! Then rig up a microphone and a small speaker, and hide the speaker near the skull.

Q: Why don't I use the circuit board for this? A: The circuit isn't designed to work with a voice...the skull reacts, but not very well. The opamp on the board reacts best to a specific tone (see the section on making the mp3), but a person's voice only occasionally hits that tone. So the effect isn't very good.

Using the skull as an "electronic puppet" is easy and only takes a bit of practice. Then you can talk to people and tell them bad Halloween jokes, chat with them about their costumes, etc.

Step 7: Building the Motor Control Circuit

If you ordered the pre-made board, this is a pretty quick project to assemble. (Otherwise, refer to the schematic and build it yourself on prototyping board.) I suggest you do it in this order, working from the middle out to the edge:

- Put the IRF510 Mosfet in the center first; bend the leads so it lays flat and then solder it in place.
- Install the resistors, capacitor and diode, and jumper, from the center of the board outward to the edge.
- Install the mini slide switch.
- Install the IC socket.
- Install the stereo jacks.
- Finally, solder in the wires for the battery clip and connection to the motor. Tip: Add hot glue to the spot where the wires go through the circuit board, this helps keep them from breaking off. You can spot this in the picture.

About the stereo jacks: The stereo jack in the part list has standard pin spacing, but similar jacks can have additional pins for support. If you get one of those, test it with your multitester to confirm that the connections are the same, and then either clip off the support pins, or use a Dremel to drill a couple of additional holes in the board for the support pins.

You could also run wires from the board to a jack off-board, mounted in the side of a project box.

The mini slide switch is optional. It’s used to swap the channel that the beep track is on (see the section on editing the sound file for details). The switch allows you to use a track with the beep on either the left or the right stereo channel, without having to fix the sound file. However, if you want, you can skip the use of the switch and use jumper wires across the connections.

Step 8: Testing the Circuit

Here's how to test the circuit to see if it's working properly, before you connect everything up. You need a multitester (preferably one that beeps), your mp3 player, the circuit and some alligator clips.

You connect the multitester in place of the skull and set it to check for continuity. This video shows how:

Troubleshooting tip:

Q: What if you hook up the skull or other animated prop to the board, even without adding the 9V battery or hooking up any audio source, and turn the switch on, and it runs continuously (keeps its mouth open)?

A: Try reversing the battery wires, on the battery box for the skull. The circuit sinks the current through the MOSFET. The skull you have may not match the one I used 100%.

Step 9: Making the Voice & Beep MP3

There’s a good video on YouTube that explains the basic idea, although we will do it slightly differently:

Use Audacity to edit the sound file, it’s open-source and available here:

A 10Khz tone triggers this board reliably.  Here are the steps to generate one and add it to the track:

Load a sound file into Audacity.  Then split the stereo tracks into two mono tracks from the Audio Track menu (see picture - this is somewhat hard to find at first).

Now you've got two mono tracks - highlight all of the lower one and delete it.  You'll replace this with the beep tones to activate the skull.

Now generate a short beep tone by selecting the following menu items:

Generate > Tone  - This will bring up the Tone Generator dialog.  Pick the following:

Waveform: Sine or Square
Frequency (Hz): 10000    [Note: This is a different value, originally I had one more zero.  This value works better with cheaper mp3 players.]

Enter a duration such as 1 second.  You'll be cutting this up into smaller sections later.  Now click OK, and you'll get a section of wave that will trigger the jaw on the skull.  However, you usually want short sections of this tone lined up with the start of each word - see the third picture.  You can cut and paste sections of the tone to different parts of the lower track to get the effect you want.  (See the YouTube video linked above for a demo of how to do this.)

Once you've got a first pass at this, go back to the Audio Track menu and pick "Make Stereo Track".  This will combine both tracks into one.  To test the track, listen to it with headphones - you should hear the skull's voice on the left and the beeps on the right.

At this point you can test the track to see how it animates the skull's jaw, and then adjust the length of each trigger tone so it looks right.  When you use the mp3 player in the final build, you may need to turn the volume of it up so the beep track is loud enough for the board to sense it and animate the skull.

Step 10: Hooking Everything Up

My preference for this type of project is to put all the circuits (microprocessor, mp3 board, skull motor control board, and batteries) into a single project box.  Then you can conceal the box where you want and adjust the length of the cables to the skull and the speakers.  Another cable goes out of the box to the motion sensor, which needs to be hidden where it works the best. 

Here’s how I assembled it:

The microprocessor, mp3 player, and motor control board get fastened in place with either standoffs or sticky-back Velcro.  I make the connections between the boards and hold down the batteries with more sticky-back Velcro (or duct tape).  The wires to control the motor go to another mono phone jack, which is mounted on the outside of the box.  I mount the motor control board so the stereo jack which goes to the speakers is lined up with a hole in the box.  And then there’s a hole for the cable that goes to the motion sensor.

This allows me to set the skull where I want, and connect the skull to the motor control board with a 2-wire mono cable.  Plug the speakers into the stereo out jack on the skull control board, and locate the PIR motion sensor where it will work best.  I hold the lid of the project box closed with electrical tape, which makes it easy to open up and turn the power on/off.

Step 11: Additional Types of Props

This board can be used to control other types of props as well. For example, a talking raven recently came out, and it works a lot like the skull…there’s a small circuit board that plays back a sound file and turns on a motor that makes the raven move, in sync with the sound. You can remove the circuit board and connect this board instead, so you can have a talking raven.

Here's a demo of the raven I found on YouTube:

Step 12: Thanks

This was a pretty big project and wouldn't have happened without the help of two people, Gary "Otaku" Adams, and Phil Short. They did the hard lifting of the electronics design and finalized the circuit that works well and is inexpensive.

And also thanks to Blue Point Engineering for working with us on a hobby project.

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