10.3
Example Circuits
10
SENSORS
10.3
Example Circuits
Below you’ll find some example circuits that can be attached to the sensor input.
Please regard them as a starting point that can be improved and tweaked to your
needs.
10.3.1
Light Sensor with Photo Transistor
Various types of photo transistors will work. The capacitor C1 is used to sup-
press mains frequency modulation that will be captured when using LED or
fluorescent lighting.
10.3.2
Touch Sensor
This circuit can be used to convert skin resistance to a control voltage. You may
want to vary R1 to adjust the sensitivity. The capacity C1 is intended for filtering
since your body will probably pick up more noise than desired.
10.3.3
Microphone
This example circuit shows that you can even power a low-current opamp via
the sensor input’s pullup resistor. It consists of a microphone amplifier and a
rectifier with a hold capacitor. You can use this to generate a trigger signal by
clapping your hands, for example. Adjust C4 for your preferred decay time.
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