audio from bent circuits

Using Arduino Project Guidance
1

I would like to include recorded audio from four different boards salvaged from children's toys. These "bent circuits" are battery powered with different voltages and are easily burned. Frankly, I don't know how to approach this problem. Could I use an LM317 regulator for each board to deliver precise voltage? Are transistors necessary? Can the output of the boards be wired to a single amplifier circuit?

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Could I use an LM317 regulator for each board to deliver precise voltage?

Yes. If you don't have a multimeter, I suggest you get one to confirm the voltage before connecting the audio circuit.

Are transistors necessary?

No. The LM317 can put-out something like 1 Amp, which is more than you'll be "pulling" from a typical small battery in a toy. (I don't ahve the spec sheet in front of me, but it depends on the voltage "dropped across" it and heatsinking, etc.)

Can the output of the boards be wired to a single amplifier circuit?

No!!! The general rule is that it's OK to connect two or more inputs together (such as connecting multiple amplifiers), but you should NEVER connect outputs together.

For audio applications, you need a "mixer". In this situation, you can make a passive mixer with some equal-value resistors (1k to 10k should work). Connect a resistor to each output, and connect the other ends of all resistors together and to the amplifier input. With a passive/resistive mixer, there will be signal loss. If this is a problem, you can build a [u]summing amplifier[/u] with an op-amp.

3

Thanks so much. Your suggestions have helped me avoid many, many dead ends.