I'm building a microcontroller circuit that feeds its output into a microphone input of an audio recorder. The output is a square wave. (Think old-style 3.5mm Square credit card readers).
What can I use to covert a signal in the range of 0..3V to -1..+1V? I'm looking for something like MAX232, but with lower voltage levels.
I could just use a voltage divider and feed 0..+1V to the audio, but I understand that many audio input circuits use AC coupling and the recorded waveform can have unpredictable DC bias. This is undesirable, since the waveform encodes information in zero-crossings.
The question really is about a circuit that can generate negative voltages without a separate negative supply, but for completeness, I can add a few more details. The application is a kind of old-style telemetry format. The data rate is fairly low (~2,000 zero-crossings/second, or 2kbps). The client audio circuit is usually (though not always) a digital recorder. The client records my input and (usually) saves it as a digital sound file. Clients' expectations are that third-party programs can extract original digital information from these files. Sometimes, instead of recording my signal directly, the client feeds my signal into an audio-frequency radio TX (think walkie-talkie) and records the signal from the RX.