Lie detector based on arduino nano v3.0

Lie Detector V1.0

Preface

First of all, let me state that this polygraph system is a simple polygraph system. It only collects human body potential information to determine whether there is a possibility of lying. It is only used as an auxiliary tool and cannot be used in precision measurement locations.

Whether polygraphs are effective is still controversial internationally. Although lie detectors are widely used in some countries, their legality has always been questioned. Some criminal investigators consider it an effective interrogation tool; some psychologists insist that the physiological reactions caused by anxiety or anger are similar to those of lying, and the reliability of the test results is difficult to guarantee.

Therefore, it is recommended to make a comprehensive judgment based on multiple factors when using it, and never blindly follow the instrument analysis results.


Figure 1.0 Physical picture of polygraph

Onboard components and schematics

This series uses Arduino nano v3.0 microcontroller as the main controller. It has 8 LED indicators on board, 3 tact switches (high level trigger), passive buzzer, toggle switch, Dupont needle 2.54mm 1* 2P (with jumper cap).


Figure 2.0 Principle diagram of polygraph

Detailed function explanation

Remove the jumper cap on the DuPont pin of the connector, put the two wires on your fingers, and insert the interface into the DuPont pin to keep the connection tight and the electrical characteristics good. Power the development board through wires, use a mobile power supply or mobile phone charger, and the input voltage must not exceed 5V.

Move the switch to the lower position and the lie detector enters working mode. At this time, you can see that the power indicator light is on, and the standby command indicator light is on after a few seconds, indicating that the user needs to perform the next step.

Press MODE-A or MODE-B to select the corresponding mode:

The single-digit indicator light on the left lights up, indicating that the display has entered this mode. After a few seconds, the command indicator light goes out, and no further operation is required by the user. At this time, you can see that the voltage between the two electrodes has been read and reflected on the indicator light. The data is read every 100 milliseconds, and the indicator light will display in real time as the voltage fluctuates. (If the indicator light does not display, please use a screwdriver to adjust the resistance of the SSTN potentiometer so that the indicator light is in the state where No. I II III is on and No. IV V VI is off)

The single-digit indicator light on the left lights up, indicating that the display has entered this mode, and the command indicator light is still on. At this time, as in operation A, adjust the potentiometer to make the indicator light in the state of I II III on, IV V VI off, press again The corresponding button of mode B confirms the selection. At this time, all indicator lights are off, and the command indicator light is off. If the voltage fluctuation exceeds the set value, all indicators will light up, the buzzer will sound, and the command indicator will light up. At this time, you need to press the reload button to reset. After pressing, all the indicator lights go out, the command indicator light goes out, and you return to the detection mode.

After use, first move the toggle switch to the upper side, and then pull out the power cord of the development board to complete the operation.

Introduction to use

Mode A can be used as a real-time display for judgment. After adjusting the subject's voltage to the median value, if the subject lies, the indicator light will jump violently.

Mode B can be used as an instant reading judgment. After adjusting the subject's voltage to the median value, the indicator light will light up once the subject is lying.

Expand applications

This polygraph can connect the jumper to the Dupont needle and perform digital-to-analog conversion to read the resistance of the potentiometer.

The microcontroller can be connected to the computer through a data cable to burn programs and develop projects.

This lie detector has a PWN output, which can act as an oscillation source to drive a passive buzzer and adjust the pitch.

The program code has been uploaded as a project attachment.