I've salvaged a 4 Ohm, 1.5 Watt speaker from an old computer, and I was wondering how I'd go about getting it to work with my Arduino. I've heard of various amplifier circuits such as opamps, but I do not know which would be the best for my situation. I've also heard that using the speaker in certain ways (such as directly connected to a pin from the Arduino) could damage both the speaker and the output pin, so that is definitely something I'd like to avoid. I'm not looking for anything complicated; I'm just trying to get a feel for the general circuitry, programming, and speaker volume. Any suggestions?

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5v, 4ohm, >1amp from a pin rated for 0.04amps; this isn't safe!
You would need a driver, but it would suffice to add a small transistor & a couple of resistors to drive it; here is a slightly more complex layout, there are many examples on the web.

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