Great news! For those of you who can't read a schematic, but CAN assemble pre-made electronic kits, there is a DC Motor Speed control circuit available from the kitsrus
people. Kit 67
is the perfect way to power the 12VDC motor used in this project, and you don't need to go to Radio Shack and buy a prototype board to use!
The kit comes with printed circuit board and all parts necessary to build the project. You only need to have the equipment and know-how to solder to build this circuit.
I highly recommend this kit over the prototype I have used. The circuit I use just regulates the voltage to the motor which means it's not being driven with full-torque. Often times, the motor spins at different rates from one trigger of the circuit to the next making for inconsistent rates of shake for the skeleton inside. The advantage of this kit is it spins the motor at full-voltage, but it pulses the signal sent to the motor. So, for slower speeds, it sends short bursts of voltage to the motor and for faster speeds it sends longer bursts of voltage to the motor.
If you want to further simplify this project, I also suggest using a DC PIR circuit I found made by the same company. Kit 30
is a Infrared Sensor similar to the ones that Halloween prop-meisters usually "hack" to work with their stuff, except this one runs off of DC voltage so you can run it off the same power supply that the motor controller runs off of.
This kit also features a more adjustable "on" time than the (very limited) switch on the Hardware Store variety. The "on" time is adjusted via a potentiometer on the board.
Another great feature about the Kit 30 is the fact it has a 30 second "off" time after the "on" time has expired. This makes it so it can't be triggered again for 30 seconds. The advantage here is the same patron can't trip the thing over and over again.
If you use the Kit 30 sensor, I'd also suggest using a kit 43
Relay to send power to the motor. The kit 30 isn't recommended for "mains power switching", so what you do is have the PIR sensor trigger the kit 43 Relay which sends the positive power from the motor controller to the motor.
I'll draw a block diagram of all this someday.