Sensor Button (Finger) - Maker Factory ELECTRONICS EXPERIMENTS BOX Manual

2.53 Sensor button (finger)

Circuit 116: On button with sensor
Setup information
Install the two transistors, the LED diode and the five resistors as shown in Fig. 2.116. Finally, insert the six
jumper wires. Check the placement on the board again and only then connect the battery.
Experiment
Although everything is wired correctly, nothing will happen when you connect the battery; the LED remains
dark. This circuit is a responsive to a DC voltage amplifier with a high-resistance input. We use the bare end
of the wire jumper as a sensor. When you touch the sensor surface with grease-free fingers, the red LED will
shine brighter. If you use a relay instead of the LED, you could turn on 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. 3.116.
Components required:
1 x J111 FET transistor,
1 x 2N3904 transistor,
1 x red LED, 1 x 1 MΩ
resistor, 1 x 100 kΩ resis-
tor, 3 x 1 kΩ resistors,
1 x breadboard, 1 x 9V bat-
tery with clip connector
Fig. 2.116: On button with
sensor
141