Card exchanges love more data. You'll get much better cost rates and acceptance rates the more data you provide, and the more you get from the card the better.

Card exchanges love more data. You'll get much better cost rates and acceptance rates the more data you provide, and the more you get from the card the better. Or checking against typed in data. This is why we still use swipes at all instead of just taking a picture of the card. Converting magnetic signal to audio is a decoding and conversion. There may be more down the line, but it is still one step that can be called that. Similarly, there are plenty of pet projects out there that harvest the audio jack for power, like running an IR LED. You are just plain wrong on that point. There isn't any issue playing sound out while recording in.