This instructable will show you how to add a moving jaw to a skull, pumpkin or other holiday prop. I used this one to make my 3 Axis Skull on my Cauldron Creep talk when a motion detector went off. This circuit does not require any programming to sync up with and audio source, but I will include some arduino code to control an MP3 player for taking it further, as well as show you how to add a trigger sound to an audio file if the source audio has lots of ambient noise preventing the circuit from detecting the correct time to open and close.

Here is an early jaw test using a Charile Essers youtube video as the audio source. No editing of the original sound was made.

In most of the videos I've included you'll see either the skull moving in 3 axes with a NOD, TILT, and ROLL, or it performing a regular Cauldron Creep motion (as designed by Devils Chariot). This instructable will focus mainly on the jaw motion. I will eventually post instructables on each of the different parts but wanted to focus on each mechanism individually.

If you just can't wait for that massive set of instructions, and want to tackle that HUGE time consuming project, here are links to essentially everything else you will need:

3 Axis Skull Options:

1) Triaxial Skull Labs (I based my self build off of this design, which Don shared in another forum, but used a modified socket universal joint instead of a spring. Condolences for your loss, you will be missed)

I am loath to give out the instructions without Don's permission. The gist of it can be gleaned from these handy assembly videos on youtube, or are available HERE if you are a member of the garage of evil Halloween forum.

2) Halloween Bob's Designs

3) Skulltronix

4) DIY, here's a video of the mechanism in my skull

Cauldron Creep:

1) Devils Chariot
2) Scare FX stirring witch

DIY Cauldron:

1) I followed these steps.

I've also included tidbits, code, and other useful stuff on all of the above in the remaining steps here.

** As you can see I tend to include a storm of links in my instructables, you've been forewarned... ONWARD!!!!

Step 1: What You Will Need

I've listed some of the specific things I used in my skull, but many possible substitutions be made.

1. Hollow Skull with access to the insides - Lindberg Pirate Skull Model kit number 71302

2. Scary Terry Audio board - I had some PCBs made through DirtyPCBs.

3. Standard Servo -

4. Servo ball joint - I used the 1/16" threaded ball link by Du-Bro part number: DUB190

5. 2-56 Threaded rod - Only a few inches are required, and I've seen these carried at Lowes.

6. Servo mounting plate -

7. 3.5mm audio splitter -

8. Stereo MP3 player - Any will work but both the TDB380 or TDB381 from MDfly will work with my code.

9. Arduino or equivalent Atmel based microcontroller board.

10. Amplified Speakers - An old pair of computer speakers works great, I used a pyle pro 2x40 Watt mini amp and a pair of speakers I picked up at a thrift store for $10.

11. 2-56 Servo Clevis Links -

12. Assorted wire

13. Power supply/Wall warts



1. Passive Infra Red (PIR) motion sensor - I use the Parallax PIR Sensor (Rev A) in this example because I had a bunch of them already, but the currently sold (Rev B) works great as well and is easier to mount.

Step 2: Tools & Supplies

1. Drill (Press is ideal but a hand drill will work as well)

2. Dremmel or other Rotary tool

3. Solder

4. Xacto knife

5. Super Glue

6. Soldering Iron

7. A variety of screws, (4-40 and 2-56 were my most common in 0.5" lengths)

8. Arduino or other micro-controller.

Step 3: Scary Terry Audio Board

This is a popular circuit in the DIY Halloween community for making a prop talk. It is a modified servo tester circuit and how to make the original version is covered over on Scary Terry's Halloween Page. Myself and some friends wanted a smaller, nicer looking version, that would fit inside the skull with other circuits, and not break the bank. So we made the schematic and PCB in eagle cad, panelized it, and made a bunch through DirtyPCBs.

I've included the schematic, board layout, and the original gerbers I submitted to the board house in case you want to have your own PCBs made. (You'll get ~40 with the files I've included, but will not come individually separated). If you don't want to go through that process, or wait that long we are willing sell our extra boards, and if there is sufficient interest we can put a kit together (I obtained Scary Terry's permission to re-sell these earlier in the year as well). If you plan on spinning your own version I would highly suggest adding in the schematic updates like we did as described on the scary terry audio page.

As a word of warning we're currently editing the files I've shared here with improvements on the spacing, and routing to make the board easier to solder and use. (The potentiometers point inward currently, my bad). I also have another layout with some of the improvements as a part of my 3 axis control board, and TBD380 interface if anyone wants to pursue the 3 axis skull portion as well.

If you are intimidated by soldering but still want a nicely made board and are willing to pony up the $60 you can buy a completed Scary Terry board through cowlacious designs.

Steps are pretty simple here:

1) Obtain Board (If you'd like to buy one of our extra's just PM us, we have a few kits and raw boards for just a few bucks.)

2) Solder together using the instructions I've put in the images above.

3) Onto testing the circuit!

Step 4: Assembling Scary Terry Audio Board

We have included an Excel file with the parts list and reference designators for all of the components on the PCB.

This is where it will be handy to have a soldering Iron and basic solder tools. If you do not know how to do through hole soldering here is a link to a tutorial that Sparkfun has put together.


I would recommend you start with the resisters and capacitors first.

Also as a side note, we placed the left right channel select to close to the headphone jack on the board. So to keep it as small as possible I would solder the headphone jack to the back of the PCB as show in the picture. Also please be sure to read the notes in the spreadsheet about which lead are ground for the caps. The note about the cathode side of the LED is incorrect, the cathode or short leg of the LED goes on the LEFT not the right. The image I've included above is correct.

Step 5: MP3 Player

The type of MP3 player is not critical, I chose to use the Tenda TDB380 because it can be controlled over a serial (RS-232) port running at 4800 baud. This makes it super easy to control from a microcontroller and trigger an audio track from a PIR motion sensor. You can pick one up from MDfly or if they are out of stock, you can also get the TDB381 which is the same board but runs with a micro SD card instead of a full sized one.

Here is another type from Deal Extreme

Step 6: Arduino Hookup and Code for MP3 Player

We are using an Arduino Duemilnove for our connections. We connected the TX (pin 1 Blue wire in photo) to pin 15 of the MP3 player. We then connected the RX (pin 0 Brown Wire in photo) to pin 16 on the MP3 player. We also connected Vin (second brown wire) on the Arduino to pin 20 on the MP3 player (note: This voltage comes from the barrel jack on the Arduino not the USB. The MP3 player needs 6 to 12 Vdc in). Then connect Ground (black wire in photo) to pin 19 on the MP3 Player.

You can use either a male 3.5mm jack or female as shown in the picture. It all depends on your setup.

Solder the tip, ring and sleeve on your connector. Solder the sleeve wire to a ground pin on the Arduino. Solder the wire on the ring to the Right channel (pin 17) on the MP3 player, then solder the wire for the tip to Left channel (pin 18) on the MP3 player.

For the 3 axis skull I wanted it to have random head movement controlled by the Arduino as well, so we designed a set of 3 boards (all through Dirty PCBs) that could be used as an Arduino Shield or as an Arduino itself that takes care of all the MP3 connections and sends the Audio, power, and 3 axis skull commands over Ethernet to minimize wires running up to the skull. Unfortunately this board had a few cuts and jumpers to it fix some errors, when I get the next rev done I will upload it as well. If anyone is interested in these boards I have a few still available.

Step 7: Configuring the Scary Terry Audio Board

*It's important to note that you should adjust these steps as necessary to prevent a servo from straining against something, as that is a sure fire way to burn it out in a few seconds, initial testing is suggested to be done OUTSIDE of the skull*

For these steps to work your audio source must provide a high enough of a volume to trigger the circuit. Potentiometer R3 (Volume/Gain) can step up most audio sources to be loud enough, but if you have a super quiet sound track you might need an additional gain such as a preamp.

1. Turn all potentiometers approximately to the middle of their movement.

2. With no sound present (unplug the audio in cable) adjust the THRESHOLD (R6) potentiometer until the LED lights up. (This means the servo should move to it's max allowed position.)

3. Turn the MAX (R9_2) potentiometer until the servo reaches the end of it's desired/allowable range and then back off a little bit so that the servo isn't straining against an end stop. This final position should be where you want the servo to open at it's maximum or jaw fully open position.

4. Turn the THRESHOLD (R6) potentiometer until the LED goes out. (This will cause the servo to move to it's minimum allowed position.)

5. Turn the MIN (R10) potentiometer until the servo is at the desired minimum (jaw closed) position. Make sure that the skulls teeth aren't fully closed so they don't make a clacking noise as the mouth shuts.

6. Connect your sound source to the Scary Terry audio input and turn it on.

7. Turn the THRESHOLD (R6) potentiometer until the LED goes solidly on, then slowly start backing off until the LED flickers on and off in time with your audio. At this point your servo should be moving in sync to your audio track playing with the Volume and Threshold potentiometers will help narrow in on the best performance.

Step 8: Editing a Sound File in Audacity

If your audio source is noisy, has background music, or there aren't loud & clearly defined pauses, the Scary Terry circuit may fail to sync up with the audio properly. If this is the case you can easily edit the sound with the free audio software Audacity. This idea was popularized for skulls by Charlie Essers on youtube and this step can be summarized in these two videos by him:

Video 1

Video 2

But I've also included the steps I used here so you can follow along, as well as a few Halloween tracks that I obtained edited from the headstorm site. The edits I did include audio for both left track trigger, right track audio; and left track audio, right track trigger.

1. Open Audacity

2. Import your sound file by clicking: File >> Import >> Audio

3. Split the Stereo sound file into two Mono tracks by clicking the tracks: Drop down arrow >> Split Stereo to Mono

4. Delete one of the tracks: Click the little 'X' in the tracks menu

5. Create a new blank audio track: Tracks >> Add New >> Audio Track

6. Change from two Mono tracks to a unique right and left track:

First Tracks Drop down menu >> Left Channel

Second Tracks Drop down menu >> Right Channel

7. Add trigger sounds to the new track at the points you want the jaw to open: highlight a portion of the track corresponding with a word, or a jaw open position and duration. Then click:

Generate >> Tone

In the window that opens choose a frequency of 12000 Hz and an amplitude of ~ 0.85 & click 'Okay'

8. Repeat this until the all the words have trigger commands

Step 9: Prepping the Skull & Putting It All Together

This step is pretty simple in principle, but will vary in exactly how everyone implements it. Scary Terry has an excellent page describing the process he used on a Bucky skull

1. Open your skull

2. Find the point on your skulls jaw that you want to actuate the jaw from. I would suggest the middle of the part of the jaw known as the Coronoid Process highlighted in red above in the first picture.

3. Attach 2-56 ball linkage or other linkage to this point on the jaw. I used a Du-Bro 2-56 Ball Link Cat No. 181 which costs $1-$2 most places

4. Drill a hole in the skull directly above this point. For me this was a half inch hold that was hidden beneath the cheekbone as shown in the third picture.

5. Mount your servo inside of the skull directly above that point. Ensuring that the servo will move in the correct direction when the Scary Terry audio circuit opens it. I created an acrylic mounting plate that my 3 axis mechanism attached to, but the servo can be mounted in a variety of ways. The first skull I made I simply hot glued the servo where I wanted it inside of a Bucky skull.

6. Connect the Jaw linkage to the servo horn with a 2-56 threaded rod and clevis.

Step 10: Our Audio Boards in Some Friends Setups

First friend made a talking skull with a Lindburg Skull and PVC pipe. He followed scary terry's instructions for connecting the servo to the jaw. He used an arduino and wave shield to play his tracks whenever someone knocked on his front door. He also used a pair of LED matrices for the eyes and had the arduino controlling the eyes.

Another friend made a talking walking stick. He bought a $5 skull and cut a hole in the back. There he made a plate out of 3/8" ply wood to mount the servo. He mounted the speaker in the skull and formed a push rod from the hobby store to make the connection between the servo and the jaw. His audio source was a Sansa clip MP3 player so he could pick and choose which tracks to play and when.

<p>Hi, I am just starting to get into animatronics as I am now retired <br>and have always had an interest in this area. I am a complete novice and<br> would greatly appreciate your help if you can spare me a few moments of<br> your time please.</p><p>I have been scouring the internet and watching <br>your youtube videos but am struggling to understand exactly what I need in terms of what parts are required to build a tri-axis skull mechanism <br>with servos.</p><p>I have the skull already so now need to understand <br>how to build the mechanism as detailed in your videos and descriptions, <br>as the sources of your parts etc are no longer available as far as I can<br> see.</p><p>If possible could someone please reply with a detailed list of ALL the parts I will need to build the mechanism including the specific <br>servos you used and any control boards/parts to operate the mechanism <br>please.</p><p>Also if you could provide direct links where I can purchase the required parts that would be very much appreciated.</p><p>Can I offer my thanks in advance for any help you can offer, it would be greatly appreciated.</p><p>Many thanks for your time,</p><p>Des (UK) </p><p>** Apologies if this question seems stupid but I really am a complete novice and providing the full list of parts and links to them would help me greatly, thank you.</p><p>If you would like my direct email address for this please message me and I will pm you the details.</p>
<p>Just terrific! Nicely done.</p>
<p>Well done! Thanks for the credit too!</p>
<p>Thank you! Your youtube tutorials made a world of difference for me in how well these would sync up with the audio. Before I'd even edited the audio I used your same youtube video as the audio to control the jaw since that would sync up really well on its own. It's on the second link on the first page showing the 3-axis mechanism working</p>
<p>I saw that and laughed out loud. The finished product is amazing. Really nice work!!</p>
<p>&quot;Re: Your Brains&quot; thats a good song.</p>
<p>:D I was really hoping somebody would have picked up on that one.</p>
<p>This is soooo cool! I love the way everything moves so naturally, not &quot;animatronic&quot; like the Hall of Presidents at Disney. Great job!</p>
<p>What a amazing project is....</p><p>Nice talking skull....</p><p>And I like qute light glasses...</p>
<p>Absolutely awesome job ! For next year Halloween I have wanted to make the jump to some animated props, and with your tutorial here I think I could easily make that happen....Thanks !</p>
<p>I got one of his board that he made and it made it so simple to make this jump. I would recommend getting one of his boards.</p>
<p>I got chills watching the video. Nice work!</p>
<p>Impressive build. Your video is awesome. It must of scared off the kiddos.</p>
Thanks, it was kind of funny actually, I had gobs of kids just sitting there staring at it. A 3 year old didn't want to leave, and a family of 5 pushed their grandma over in a wheelchair, an hour after I'd turned it all off for the night, and asked if I could turn it back on so they could sit and watch.
Look like alife. Awesome work
<p>Woah the effect is awesome! Thanks for making such awesome instructions!</p>
<p>Good design and easy to follow. I made the talking skull staff</p>

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