How to access the Sensors

Unless noted otherwise, the sensors are low power devices and always enabled.

3-Axis Accelerometer (BMA180)

read values

cat /sys/bus/i2c/drivers/tsc2007/2-0041/coord

data range

1g is approx. equivalent to a readout of 4096. The maximum is 4g, i.e. 16383. If the device is rotated by 180 degrees, the values become negative.

The axis orientation is:

• x:
• y:
• z:

3-Axis Gyroscope (ITG3200)

Enable power (shared with Compass!)

The nominal analog voltage of the chip should be 2.5-3.0 V

VDD=2800000
echo "$VDD" >/sys/devices/platform/reg-virt-consumer.2/max_microvolts
echo "$VDD" >/sys/devices/platform/reg-virt-consumer.2/min_microvolts
echo "normal" >/sys/devices/platform/reg-virt-consumer.2/mode

disable power

echo "0" >/sys/devices/platform/reg-virt-consumer.2/max_microvolts

enable sampling (chip is in power down after reset)

echo "0" >/sys/bus/i2c/devices/i2c-2/2-0068/suspend

disable sampling (to save some power)

echo "1" >/sys/bus/i2c/devices/i2c-2/2-0068/suspend

read values

cat /sys/bus/i2c/devices/i2c-2/2-0068/values

3-Axis Compass (HMC5883L)

Enable power (shared with Gyroscope!)

The nominal analog voltage of the chip should be 2.5-3.0 V

VDD=2800000
echo "$VDD" >/sys/devices/platform/reg-virt-consumer.2/max_microvolts
echo "$VDD" >/sys/devices/platform/reg-virt-consumer.2/min_microvolts
echo "normal" >/sys/devices/platform/reg-virt-consumer.2/mode

disable power

echo "0" >/sys/devices/platform/reg-virt-consumer.2/max_microvolts

read values

cat /sys/bus/i2c/devices/i2c-2/2-0068/values

Barometer and Thermometer (BMP085)

cat /sys/bus/i2c/devices/i2c-2/2-0077/pressure0_input
cat /sys/bus/i2c/devices/i2c-2/2-0077/temp0_input

Pressure is in Pa. Temperature in 1/10 deg C.

Touch Screen Position, Pressure/Resistance, Temperature and (optional) Ambient light intensity (TSC2007)

The raw ADC values, plate resistance, the temperature sensors and the AUX input (optional ambient light sensor) can be read through

cat /sys/bus/i2c/drivers/tsc2007/2-0048/values

The order of the values is

x, y, pressure, pendown(0/1), temp (in 1/10 deg C), z1, z2, temp0, temp1, aux, resistance

The temp and aux values are updated every 100ms and the other values only on pen-down every 1ms.

Pressure values are an estimate and are lower for touches with small area (fingernail, stylus) and higher for bigger touch area (finger tip or multitouch). Typical range:

• 300 for stylus
• 700 for finger tip
• 2000-15000 for two fingers

Resistance is an estimate with a reference value of 600 Ohms.

Note: the x and y values are the raw values before any calibration (which is usually done through libts or similar means).