SoftModem

SoftModem is a wired, low-cost and platform independent solution for communication between an Arduino and mobile phones. It uses the phone's audio jack and Bell 202 modem-like FSK encoding with up to 1225 bit/s. Check out this blog post.

Projects based on SoftModem:

• SoftModemTerminal by Arms22: an iOS SoftModem terminal application
• FSK-Serial-Generator by NeoCat: a JavaScript transmitter implementation
• WebJack by PublicLab: a JavaScript transmitter and receiver, compatible with Firmata.js/Jonny-Five

Install via Arduino Library Manager

Open the Arduino Library Manager from the menu: Sketch → Include Library → Manage Libraries.... Then search for 'SoftModem' and click install.

Manual install

Create a folder 'SoftModem' inside your libraries folder and place these files there.

Supported Boards

• ATmega328: Arduino Uno / Nano / Pro / Pro Mini / Fio
• ATtiny85, ATmega32U4: not implemented yet, contributions welcome!

Usage

This is an example sketch that forwards data to/from the serial port.

#include <SoftModem.h>

SoftModem modem = SoftModem();

void setup() {
  Serial.begin(115200);
  Serial.println("Booting");
  delay(100);
  modem.begin();
}

void loop() {  
  while(modem.available()){
    int c = modem.read();
    if(isprint(c)){
      Serial.print((char)c);
    }
    else{
      Serial.print("(");
      Serial.print(c,HEX);
      Serial.println(")");      
    }
  }
  if(Serial.available()){
    modem.write(0xff);
    while(Serial.available()){
      char c = Serial.read();
      modem.write(c);
    }
  }
}

Notes

SoftModem uses Timer2, therefore you can not make use of the analogWrite() function for pins 3 and 11 in your sketch.

Hardware

A shield is available here or here. You can also build your own. Here is the schematic:

License

BSD 3