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| The OLPC XO can measure external inputs with its microphone jack | | The OLPC XO can measure external inputs with its microphone jack |
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− | Specifications | + | ==Specifications== |
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| Standard 3.5mm 2-pin switched mono microphone jack; selectable 2V DC bias; selectable sensor-input mode (DC or AC coupled) | | Standard 3.5mm 2-pin switched mono microphone jack; selectable 2V DC bias; selectable sensor-input mode (DC or AC coupled) |
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| If using a stereo plug it is the red wire plus the earth. | | If using a stereo plug it is the red wire plus the earth. |
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− | It is protected at the input by a 5V zener diode and has a measurement range of 0.3V to 1.9V. The allowable input is -0.5V to 5V Inputs outside this range will cause excessive current and damage. | + | 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. |
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− | 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. | + | 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 mictophone plug and a series resistor. |
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| + | ==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. |
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| + | ==Resistance Mode== |
| + | Measurement range is 750 ohms to 16k ohms, resistances less than 750 ohms report as 750 ohms, greater than 16k ohms. Accuracy is around 5% with respect to the voltage measured accross the resistor, this translates to round 50 ohms at bottom scale and 2k ohms at top scale. |
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| + | ==Pitch Mode== |
| + | Pitch Mode is set up for the internal microphone but can be accessed through the microphone jack. 2V DC bias is on, AC coupled, +20dB boost is on. The resolution is +-8Hz |