Max Voltages on Tape Heads

I want to make an Arduino project that reads magnetic stripe info from old gift cards and converts the signal to a simple tone sketch that will "play" the cards in total glitchy delight. Kinda similar to Sylvia's (of Sylvia's Super Awesome Mini Maker Show fame) arduino project featured by Make Magazine. (It took the voltage variation in your skin and converted it to tones)

Two things: 1. What are the max allowable voltages into the analog pins on the arduino? I don't wanna fry it.

  1. Any idea what voltage peak I would see by running gift cards against an old tape head? I guess the easiest way to do that is try it and measure the voltages. I imagine I could just add a limiting resistor in series, and I'll have to figure out that value as well.

Thoughts? :)

  1. What are the max allowable voltages into the analog pins on the arduino? I don't wanna fry it.

+5V maximum.

  1. Any idea what voltage peak I would see by running gift cards against an old tape head?

I don't think you see any voltage. I think the head has to excite the card to read the data. That means that the head has to be powered.

I imagine I could just add a limiting resistor in series, and I'll have to figure out that value as well.

My guess is you need more than that.

You can buy card readers (for example: http://www.sparkfun.com/products/8633)

I'm not sure you could read the data on a card with a magnetic tape head (like from a cassette tape player), but it may work if you try hard enough. With an amplifier (like a low noise opamp) you may get a "signal" though it'll probably just look like noise though, which may be what you're after.

I don't think you see any voltage. I think the head has to excite the card to read the data. That means that the head has to be powered.

You don't have to excite a card to read it. The magnetic field as the card is swiped induces a (extremely tiny) current in the read head. This means that the coil looks like a current source NOT a voltage source, so the voltage "seen" will depend on the input impedance. You'll have to experiment and odds are good that you'll actually need an amplifier to get any signal at all.