SainSmart HMC5883L Digital Compass Module 3 Axis Magnetoresistive Sensor for Arduino UNO MEGA R3 Mega2560 Duemilanove Nano Robot SainSmart HMC5883L Digital Compass Module 3 Axis Magneto resistive Sensor Board size: 16mm 18mm Supply voltage: 3.3V or 5V Pin spacing: 2.54mm