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Lesson 32 Lie Detector
Introduction
How can an Evil Genius be sure that their prisoners are telling the truth
?
By a lie detector, of
course. This lie detector uses an effect known as galvanic skin response. As a person
becomes nervous – for example, when telling a lie – their skin resistance decreases. We can
measure this resistance using an analog input and use an LED and buzzer to indicate an
untruth. Use a multicolor LED that can display red to indicate a lie, green to indicate the truth,
and blue to show that the lie detector should be adjusted by the variable resistor.
Components
-
1 * SunFounder Uno board
- 1 * USB data cable
- 1 * RGB module
- 1 * Buzzer module
- 1 * Potentiometer (250k)
- 1 * Resistor (470k)
- Several jumper wires
Experimental Principle
The subject’s skin resistance is measured by using the test subject as a resistor in a potential
divider and a fixed resistor as the other. The lower their resistance is, the more analog input 0
will be pulled towards 5V. The higher the resistance gets, the closer to GND it will become.
The buzzer, despite of the noise level these things generate, is actually quite low in current
consumption and can be driven directly from the SunFounder Uno digital pin. This experiment
uses an RGB LED. In this case, however, we are not going to make it flash mixed colors but
just turn one of the LEDs on at a time to display red, green, or blue.
Experimental Procedures
Step 1:
Build the circuit
RGB Connection
: Connect pin R to digital pin 9, G to digital pin 10, B to digital pin 11, and pin
- to GND
Buzzer Connection
: Connect pin S to digital pin 8, + to 5V, and pin - to GND
Potentiometer Connection
: Connect the middle pin to analog port A1, and the other two
pins to GND and 5V
Resistor Connection
: connect one terminal to analog port A0, and the other to GND
Then, take out two jumper wires, and connect one end of one jumper wire to A0 and one
end of the other wire to 5V.
SunFounder
