[Kevin Sevcik]

Other options available are DC tachometers, if you can find them cheap, or other crazy IC circuits. The frequency to voltage converters appear to be able to operate from 7.2V, I'm unsure about 5V, and I can't tell you how well they'll work at the moment. Any of these analog input options have certain advantages and disadvantages over digital encoders. The main advantage is that you can sample at otherwise unreasonable frequencies of 100+Hz and still get higher resolutions of more than 100 steps. Trying this with an encoder would give you 10,000 intrerrupts a second at top speed, and likely leave your processor a quivering pool of molten silicon. You can also get up to 10-bits of resolution, provided you design your circuit to provide such. The downside is you're working in the analog world and now have to deal with temperature effects and such. Such is life, but I think the pros outweigh the cons if you can pull it off.