View Full Version : Hacking cheap talking skulls? Would DCSSR work?

03-13-2012, 12:23 AM
Nice talking 3-axis skulls appear to be pretty expensive.

I was considering starting with a cheap mass produced one, like this:


(This one is also available many other places; and I'd be interested in links to better ones)

Here's an article on somebody who used a color organ to make the jaw (plus added eyes) respond to sound.


I'm wondering if a DCSSR (or other DC dimmer) would work for animating the jaw in a proportional manner.

Also - has anybody else tried these skulls? It's not clear how the motors are connected to the jaw.

03-13-2012, 09:14 AM
Typically servo's are used to connect to the jaws. A little more google work and you can find *all sorts* of references and designs for doing so. The things about SERVO's is that the value you send from Vixen becomes an actual rotational angle, versus a rotation speed. This makes it much easier to control, as you wouldn't have to track the location of the object under control.


Edit: Check out Halloween forums, as well as the article in "Nuts and Volts".

I don't have one (yet), but I've done some reading.

03-14-2012, 04:46 PM
The skull you pictured would have a motor not a servo operating the jaw. The motor spins one dirction when powerd and rotates opposite direction because of force from a spring. Color organ is a cheap way but has it downfalls. I have done one simular years ago the following way. Remove the wires from the battery pack. hook up a dc walwart to the wires that were removed from the battery pack. Voltage will vary from skulls. Some may be 2 AA 3vdc or 3 AA 4.5vdc. hook the ac part of the wla wart to the color organ. As sound is picked up from the organ it opens and closes the circuit like a relay which will allow ac to flow to the walwart that converts it dc. Only problem with most color organs is that they have an external mic that picks up the sound. Mine actually hooked directly up with a speaker wires so as the sound played the jaw moved. You may have to remake the audio track as the organ picks up differnt types of tone but most have some sort of knob that you can turn to adjust sensitivity.

i don't see is no reason that you can't hook renard up to have it switch a relay that flips dcvoltage on/off.

03-14-2012, 05:21 PM
Good info, thanks.

I was imagining that the color organ was producing PWM dimmed AC based on sound intensity, and that if the wall wart was unregulared DC, then the DC might also be variable voltage going into the motor. Do you know if the motor is essentially on/off or if it does anything proportional? (Eg: at full voltage opens the mouth to max, but at lower voltage may only pull the spring part way for a partially open mouth.)

It's not the season to see these in person in the stores, but I need lots of plan-ahead time, hence my questions of those actually familiar with the product. Thanks.

03-15-2012, 01:36 PM
Motor is only on/off there is no controllong how far it will rotate like a stepper motor or servo. Less voltage may not drive the motor at all and if it does then the mouth may move some but not full opening as it would not have the power to pull the spring tension. I have a skull that I can show you how it would work but unfortunatley my home laptop crashed last night so I am not able to make a video and upload it to youtube. Think it is a mother board issue. At least that is what I am hoping for because if it is a hard drive issue I am up a creek without a paddle as I have all my info that deals with vixen, renards, halloween stuff and all that other good stuff. Since HW is still a few months away I will get another laptop, make a vid and maybe it will help.

I think I still have a schematic of making a small board 2"*2" that you can hook your audio to to drive a motor but that too is on my hard drive.

Jeff Millard
03-17-2012, 05:06 PM
Here's the results of my attempt at hacking the cheapo Wal-Mart Skulls. (https://vimeo.com/3040939)

03-17-2012, 09:55 PM
Here's the results of my attempt at hacking the cheapo Wal-Mart Skulls. (https://vimeo.com/3040939)
They look great. How do they get that much movement(and that fast) in the jaws. It's much better movement then I get from my servos.

Jeff Millard
03-17-2012, 10:48 PM
As was discussed earlier, the jaw is spring loaded to close. There's a DC motor with a reel that winds up a string to pull the mouth open. Motor on, fast open, motor off, fast close. Caveat... string doesn't last. Additional Caveat... uncontrollable mouth postitions. There are servos that are fast enough to reproduce this action. 60 in .06 seconds. However, they're pricey. Around $80 for the 5V version.

They were controlled using a USB DIO controller for on/off via LOR software. The 2 pics are a PCBexpress layout of the original circuit board and the modded one with the unneeded parts removed.

Here's my discussion from another Forum:

The skulls came from Wall Mart. It had a little circuit board in it, that had transistors that were used to switch DC motors on and off. There was a little prom with the voice, and digital outputs that hit the transistors. I took a picture of the trace side of the board and enlarged it. I followed the color coded wires from the two motors, and the LEDs in the eyes back to the board and commented the picture. A little bit of detective work following the traces back to and through each transistor to the trace that jumped onto the prom board, I was able to find which of those traces moved the eyes 1) left or 2) right, 3) opened the mouth (it's spring loaded to close) 4) Lit the eye LEDs. I bought a Measurement Computing USB DIO 24. I used LOR to synch the mouth and eye movements with a sequence that was given to me by another LOR user. The DIO outputs at + 5vdc, (source) and the transistors needed a low from a 9v battery to fire. I made a buffer using a ULN 2803 chip that uses darlington pairs to isolate and invert. So, powered by a 9 volt power supply they output a low that will trigger the transistors when the DIO channel inputs +5v. I didn't have to modify the skulls other than to strip some of the uneeded parts like the audio amp and the prom, speaker and wires etc. I just soldered short pigtails to the traces that lead to each trigger. Molex connectors to a couple Cat5 cables that connect to the ULN buffer, and outputs from the USBDIO to the ULN inputs. All in all I think the hardest part was removing the hot melt glue they used to stash wires and hold things together. Figuring out the circuits was very easy because of the way each was isolated. The motor even had a common design that was able to reverse polarity using two 9v lows. After all the fun I had getting it to work, I found that the string that pulls the mouth open when the motor winds up... is just a cheap crappy string. It wears out fast and replacing it is a bitch. Later I decided to try Servos, but nothing I can find is fast enough to open and close the mouth. I had a bunch of suggestions from people along the way but nothing is cheap enough to justify the 10 or 15 people we get each year at Halloween.

03-18-2012, 10:20 AM
Jeff, is there not enough room for a solenoid? A linear motion would certainly be quicker than a rotational movement that’s converted to a linear. You can also use an initial higher voltage for a short time to accelerate the initial movement. Dumping a small capacitor charged through a current source is one such way.

A solenoid also is a better design for heat dissipation. You can run excessive current for a short time as long as you don't get too wild and allow some cool off time.

A steel fishing leader makes a pretty good string and a lot more pull force.

Jeff Millard
03-19-2012, 08:03 PM
I really like the idea of a solenoid Ernie. Finding the right angle to dissipate the motion could be tricky though. I'll look and see what I have when I get back to work next week. I think the circuit to wind that motor up is probably sufficient to yank a solenoid hard enough to open the mouth. This is the first suggestion I've had since I made these things a few years ago I really feel like taking the time to investigate. Everything else was complicated or expensive. A couple mock-ups might be needed but I think it could be worked.

As for the leader I tried. I would need to create some sort of reel as it doesn't like to be spun unguided and tended to overlap itself and bind without motor tension during the spring recoil. I can't recall how many rotations it took to open the mouth fully but it was more than enough to get layers of wraps to tangle as the motor tension was released. The ultimate would be use the leader, and the same circuit on the mouth motor as the eyes. If you could reverse the motor to close the mouth there would be tension on the leader and it wouldn't have the slack that occurs when it overlaps. The sequence would be a pain. You could flip the 2 channels, but you'd only need the tension to close there for a bit otherwise there would always be reverse motor power.

I think I'll start looking for a suitable solenoid and try to see what I can come up with on the spare skulls I have. Thanks Ernie, I like it! This just might reincarnate the dead heads...


03-20-2012, 12:24 PM
I think I would try and drive it with a DCSSR. By using low end values from vixen and varying the voltage to the SSR,
you may find a range that will move the motor against the spring and give you partial opening of the jaw.
I have a Boris skull that I have been thinking about trying this on.
Just a thought,

03-20-2012, 01:45 PM
I think I would try and drive it with a DCSSR. By using low end values from vixen and varying the voltage to the SSR,
you may find a range that will move the motor against the spring and give you partial opening of the jaw.

Yes! That's exactly what I was wondering about - PWM modulating the motor power and finding where a given power level balances against the spring tension. I guess that a more controlled closing could be part of the picture as well, and help with the spooling of the string. Tho the speed of these is impressive and due in part to that "let 'er rip" jaw closing.

That's a better skull than I found online looking at this time of year - it also has moving/lit eyes, tho the jaw mechanism sounds very similar to what I did find (I didn't catch this bug until a couple of months ago so I wasn't looking retail at the right time of year). I'd like to be already prepared when the halloween stock hits the shelves.

03-20-2012, 02:08 PM
It’s called proportional control and it’s widely used for controlling air/hydraulic valves everywhere and should work equally well for solenoids. The PWM frequency needs to initially be higher than what is needed to actually move the plunger. The range can be anywhere from 45 - 1000 Hz, a bit higher if it’s audible.

Depending on the solenoid, you may need to add an additional force initially to the plunger movement to overcome sticktion.

03-20-2012, 04:28 PM
Just to be clear, there are two levels of modification under discussion here. The simplest is varying the power to the existing motor with their windup strings. No mechanical modification would be needed to this beyond feeding controlled power to the motor.

The second level would involve replacing the motor with a solenoid and controlling that. That could potentially be very cool, if afforidable. Do you have any suggestions for an appropriate solenoid? (links?)