Convert a totally underwhelming foam skull into a Halloween speaker system.

-=Backstory=-

I was at Abott's party store in Littleton, NH a couple days ago and saw a foam skull. Upon first glance it looked like your basic Halloween prop, until I saw the LEDs in its eyes. I immediately knew this would be the prop of a lifetime... with the sort of technology it was hiding in its cranium, the skull might be able to:

a) Scare the daylights outa the neighborhood kids
b) Dispense fortunes when it detected questions directed at it
c) Do the dishes, walk the dog and fetch me a beer
d) All of the above

With visions of sugarplums dancing in my head, I reached down with hands trembling in anticipation and flicked the "ON" switch.

Its eyes lit up.

they didn't even blink.

I was utterly devestated.

It was then and there that I decided to remedy this great injustice. I purchased the skull and began brainstorming.

Ten Redbulls later I hit upon an idea...
What if the skull could talk...
what if his eyes lit up while he talked...
Brilliant!

so I set to work...

Step 1: Gathering Materials & Disassembling

I used the following materials for my skull:

note: double all amounts for stereo setup

1x foam skull with led eyes ($12.99)
1x 8ohm speaker (scavenged)
1x TIP31 npn transistor ($1.59 at radioshack, :( )
1x 1/8th inch mono phone jack (6 for $3.99 at radioshack :( )
1x stereo to mono 1/8th inch adapter ($2.99)
lots of thin wire (scavenged from a previously mutilated usb cable)
soldering skills

The first step is to remove the four screws holding the base on and snip the wires to the leds, leaving a stripable amount attached to both the LEDS and the battery box

Step 2: Build Circuit

build the circuit shown below from your components...

Their are two essential, traceable circuits in the overall diagram they should go as follows

Light Circuit:
positive terminal of battery box unit goes to LEDs (in series)
negative terminals of LEDs go to transistor's Collector pin
transistor's Emitter pin goes to battery box unit's negative terminal

Controller Circuit:
Positive terminal of phono jack goes to speaker and transistor's Base
Negative terminal of phono jack goes to speaker and transistor's Emitter

Step 3: Drill Skull - Mount Adapter

drill a hole in the back of the skull's cranium about 3/8th inch in diameter and enlarge it slowly until the first 3/4 of the stereo to mono adapter fit snugly. Then hammer the adapter into the foam until flush with the skull. It should form an extremely tight press fit.

Step 4: Mount Speaker

you could use pins, epoxy or short screws...
I used hot glue.

forgive me.

Step 5: Plug in Phono Jack

carefully fit the wired phono plug onto the press fit phono jack

Step 6: Close, Suture, and Test

re-assemble the skull and attach to a powered audio source (headphone or speaker jack) the skull's eyes should pulse with changes in volume.

For stereo action, you'll need to create a second skull and a special patch cable...
for the patch cable cut the cord of a set of headphones, seperate the left and right channel's wires and attach a mono phono jack to each channel

I found that the sound source needs to be pretty loud, so a Boostaroo or similar headphone amp is a godsend, but a loud audio file works just as well.

now for Ideas for use:

1) connect to aux out at a halloween party and place accordingly (on speakers, mantel, table, ect)
2) connect to mini fm radio and use a tunecast-style transmitter to play selected clips
3) mount on mannequin in grim reaper robes
4) connect to PC and use a webcam as a motion detector to play selected messages
5) Paint metallic silver and mount on hydrolic skeleton to create a working t1000 series robot... then send it back in time to protect Sarah Connor and stop the rise of SkyNet

Have fun!!