Lighting the neon and syncing it to the robot's voice is not hard, as long as you have a good device to do it with. The Tech2000 model 8000 neon transformer and music interface, are an excellent 12 Volt solution to lighting and syncing the neon.
You can contact Tech2000 directly: (760) 431-7144. Tell them you need the transformer and music interface for the robot neon, and they will know exactly what you need and they will also include the needed diodes. It is the Model 8000, 12V unit.
The Tech2000 music interface works VERY well to sync to the robot's voice, but it does require an amplified sound source. Hooking it directly from a portable CD earphone jack will not work, it must go through some type of amplifier to increase the signal. I used the amplifier from a cheap pair of computer speakers for this purpose. I kept it separate from the audio amplifier I use for my robot speakers.
The Tech2000 setup does have a few problems, but they are fairly easy to overcome. Without any fixes, the neon will show a "beading" effect when lit. The glowing neon actually looks like beads from a necklace. This can be corrected by adding one or two Zener diodes, which Tech2000 will supply. Also, the music interface puts out a weak signal that doesn't fully turn on the neon to its maximum brightness which also adds to the beading problem. That can be easily fixed by adding a transistor to boast the output of the music interface so it supplies 12V to the transformer control input. Use a "TIP31" NPN transistor from Radio Shack, only $1.29. That fix works great and the neon will now light very bright without any beading!
Setup the neon and electronic parts on a table before installing it in your robot, and test everything before soldering. In order to light the neon for testing without an audio source, you can temporarily jumper the CONTROL input (Orange wire) on the TRANSFORMER to 12V (Don't connect the music interface orange wire output to 12V!!) Now the neon should be lit, and you may see the "beading" problem. The diodes can go anywhere in the high-voltage circuit, and you should experiment with putting the diode or diodes in different places in the circuit. Find the combination that works best to eliminate the beading. If two diodes are used, they must go in the same orientation. In other words, the diodes must face the same direction when you follow the circuit loop around. The neon circuit should be one big loop, there is no positive or negative side.
Hook up the audio source to the music interface and test the whole setup.
(Click here to view a wiring diagram)