Activities/Turtle Art/Using Turtle Art Sensors
CAUTION. APPLYING EXTERNAL POWER SOURCES TO THE XO LAPTOP'S MICROPHONE INPUT CAN CAUSE PERMANENT DAMAGE. BE SURE YOU READ AND UNDERSTAND THE FOLLOWING BEFORE CONNECTING POWER SOURCES TO YOUR LAPTOP.
Specifications
The OLPC XO can measure external inputs with its microphone jack.
Standard 3.5mm 2-pin switched mono microphone jack; selectable 2V DC bias; selectable sensor-input mode (DC or AC coupled); selectable +20dB boost.
If using a stereo plug it is the red wire plus the earth.
It is protected at the input by a 5V zener diode and has a measurement range of 0.4V to 1.85V. The allowable input is -0.5V to 5V. Inputs outside this range will cause excessive current and damage.
Addition of a 150k ohm series resistor would (I expect, no guarantee) give a reduced sensitivity in voltage mode (0-4V) but allow inputs to +- 100V without damage. Input impedance in resistance, volume and pitch modes is much lower but a 1k ohm series resistor should still allow inputs to +-12V. If applying an external voltage, it is highly recommended that test leads be made up with a microphone plug and an inbuilt series resistor.
Voltage Mode
Measurement range is DC 0.4V to 1.85V. Voltages less than 0.4V report as 0.4V, voltages greater than 1.85V report as 1.85V. Accuracy is around 3% of full scale.
Resistance Mode
Measurement range is 750 ohms to 16k ohms, resistances less than 750 ohms report as 750 ohms, greater than 16k ohms report as 16k ohms. Accuracy is around 5% with respect to the full scale voltage measured accross the resistor, this translates to round 50 ohms at bottom scale and 2k ohms at top scale.
Pitch Mode
Pitch Mode is set up for the internal microphone but can also be accessed through the microphone jack, 2V DC bias is on, AC coupled, +20dB boost is on. The resolution is +-8Hz
Links
http://wiki.laptop.org/go/Hardware_specification http://wiki.laptop.org/go/Talk:Measure http://wiki.laptop.org/go/Measure/Hardware http://bugs.sugarlabs.org/attachment/ticket/552/sensor%20gain.xls