Maker Factory ELECTRONICS EXPERIMENTS BOX Manual page 190

Circuit 167: FET lie detector with moving-coil instrument
Setup information
Install the transistor, the LED diode and the three resistors as shown in Fig. 2.166. The five 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
needle is not moving. If you touch the sensor with your wet (but grease-free) hands, the needle deflection
will be more or less strong. If the anxiety level rises when a person lies intentionally, the 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. 3.167.
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Components required:
1 x J111 FET transistor,
1 x 10 kΩ resistor,
1 x 22 kΩ resistor,
1 x 1 MΩ resistor,
1 x moving-coil instru-
ment, 1 x breadboard,
1 x 9V battery with clip
connector
Fig. 2.167: FET lie detector
with moving-coil instrument