Sensors

Sensors may be used to provide flight telemetry.

The following sensors are, or will be, supported by ArduinoRCLib:

• L3G4200D; Triple axis MEMS gyroscope
• ADXL345; Triple axis MEMS accelerometer
• HMC5883L; Triple axis magnetometer
• BMP058; Barometric pressure sensor/thermometer

A gyroscope may be used to detect rotation, it can also be used to keep track of a heading/bearing.
An accelerometer measures changes in speed (acceleration). Since gravity is a constant acceleration downwards, it can also be used to check whether your aircraft is upside down or not.
A magnetometer measures magnetic fields. Since our planet has a pretty big magnetic field it can also be used to check which way the nose of your aircraft is pointing, including up and down. It's a great addition to the gyro and accelerometer since it provides some absolute values.
The barometric pressure sensor measures air pressure. Since air pressure at higher altitudes is lower than at ground level, it can be used to get a rough estimate of the altitude. Air pressure can also be used in weather forecasts, but that's boring. There's also a thermometer included.

Pictures below you'll see a PCB with a L3G4200D, ADXL345, HMC5883L and BMP085. The smaller red PCB has a BMP085 on it.