I have a device that is sending 9600baud using only Tx, Rx, and Gnd. I am not sure, but I think the voltage is either the 3v or 5v level.
I want to receive that serial data on my mobile phone.
I have found AFSK code for decoding on the mobile phone, however I am concerned about sending the 3 or 5 volts into the microphone circuit.
Can anyone help me understand what I need to do to the RS-232 voltages in order to step them down properly for the microphone circuit on the phone?