Lie Detector - Maker Factory ELECTRONICS EXPERIMENTS BOX Manual

2.78 Lie detector

Circuit 166: FET lie detector with LED indicator
Setup information
Install the transistor, the LED diode and the three resistors as shown in Fig. 2.166. The six jumper wires
come next. Two bare wire ends serve as skin sensor. Check the placement on the board and only then con-
nect the battery.
Experiment
Our circuit is a simple DC voltage detector. As long as the two sensors are isolated from each other, the LED
remains dark. If you touch the sensor with your wet (but grease-free) hands, the LED will shine brightly. If
the anxiety level rises when a person lies intentionally, sweaty palms of the hands could be taken as an
indication that the person is not telling the truth.
The circuit diagram for this experiment is shown in Chap. 3, Fig. 3.166.
Components required:
1 x J111 FET transistor,
1 x red LED, 1 x 10 kΩ
resistor, 1 x 22 kΩ resis-
tor, 1 x 1 MΩ resistor,
1 x breadboard, 1 x 9V
battery with clip con-
nector
Fig. 2.166: FET lie detector
with LED indicator
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