After one month waiting for it, I already have here my Audio Jack modem for Android (and iPhone).
With this board, data communication between Arduino and Android become possible . The communication speed is 1225bps. It is suitable for a small amount of data communication like switch inputs and sensor information.
The audio jack is included in this kit but not pre-soldered. Also, you may need a pin header or a pin socket to this board. But neither pin header nor pin socket is included, so you have to prepare it by yourself.
* Because data communications with this device uses audio, data corruption may occur sometimes. I consider incorporating checksum processing and retrying.* Please set the device's volume maximum.
Please use gold plated shielded cables. The shorter the cable, the better. In order to minimize the communications error
Connect to Arduino as follows (right side is the Arduino's pin.)
FSKOUT → D3
GND → GND
VCC → VCC
FSKIN → D6
AIN1 → D7
Volume AdjustmentMeasure the voltage on AIN1 with tester to make it (VCC / 2) + 300mV.
5V VCC: 2.7V AIN1
3.3V VCC: 1.95V AIN1