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How to Make a Lie Detector Machine

Polygraph machines, also called lie detectors, measure certain physiological responses that are created by various applications of stress. A professional apparatus measure heart rate, blood pressure, and galvanic skin response. Most homemade devices measure skin response only. As long as the machine's limitations are understood--it can't actually detect lies, just variations in physiological responses--they can be an interesting, even entertaining, pastime.

Things You'll Need

Electrical box enclosure
4.7K Resistor
82K Resistor
0.01uF Capacitor
2N3904 Transistor
2N3906 Transistor
2-AA Battery holder
Small circuit board
Spare PC speaker
Velcro
Aluminum foil
Wire
2 x AA batteries
Soldering iron
Solder
Screwdriver
Hot glue
Drill
Small drill bit
Wire strippers

Instructions

- 1
  Build the ciurcuit board. The wiring schematic for building the circuit board is available at Instructables.com. This is the step where the most patience is required. Make clean, solid solder joints.
- 2
  Place the circuit board into the box enclosure. Mark and drill holes for the wire to the finger pads. Drill a few small holes near the speaker.
- 3
  Cut two strips of Velcro long enough to reach around a large adult finger. Attach two corresponding strips of aluminum foil onto the sticky "soft" side of the Velcro strips. Glue the finger pad leads that extend from the box to the aluminum foil strips on the finger pads. Trim half an inch from the hook-side of the Velcro strips so the finger pads will overlap and attach.
  
  Start asking questions. If the circuit board is wired correctly, the speaker will make a noise if it detects a spike in galvanic reaction, or how electricity flows across the skin.

Educational Toys