Maker Factory ELECTRONICS EXPERIMENTS BOX Manual page 140

Circuit 117: Off button with sensor
Setup information
Install the two transistors, the LED diode and the ten resistors as shown in Fig. 2.117. Finally, insert the 11
jumper wires. Check the placement on the board again and only then connect the battery.
Experiment
If everything is wired correctly, the red LED will turn on once the battery is connected. This circuit is respon-
sive to a DC voltage amplifier with a high-resistance input. We use the bare end of the inserted wire jumper
as a sensor. When you touch the sensor surface with grease-free fingers, the red LED will turn off. If you use
a relay instead of the LED, you could turn off your lights or the audio system with just a tap of your finger.
The circuit diagram for this experiment is shown in Chap. 3, Fig. 3.117.
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Components required:
1 x J111 FET transistor,
2 x 2N3904 transistors,
1 x red LED, 1 x 1 MΩ resis-
tor, 2 x 220 kΩ resistors,
1 x 100 Ω resistor,
1 x 10 kΩ resistor,
1 x 4.7 kΩ resistor,
1 x 2.2 kΩ resistor,
3 x 1 kΩ resistors,
1 x breadboard, 1 x 9V bat-
tery with clip connector
Fig. 2.117: Off button with sensor