Touch Activated Light
The circuits below light a 20 watt lamp when the contacts are touched and the skin resistance is about 2 Megs or less. The circuit on the left uses a power MOSFET which turns on when the voltage between the source and gate is around 6 volts. The gate of the MOSFET draws no current so the voltage on the gate will be half the supply voltage or 6 volts when the resistance across the touch contacts is equal to the fixed resistance (2 Megs) between the source and gate.
The circuit on the right uses three bipolar transistors to accomplish the same result with the touch contact referenced to the negative or ground end of the supply. Since the base of a bipolar transistor draws current and the current gain is usually less than 200, three transistors are needed to raise the microamp current level through the touch contacts to a couple amps needed by the light. For additional current, the lamp could be replaced with a 12 volt relay and diode across the coil.
Touch Activated Light circuit
Title: Touch Activated Light
electronic circuit
Source: unknown
Published on: 2007-07-21
Reads: 2567
Print version:
Other electronic circuits and schematics from Motor, light and power control
-
Brightness Control for small Lamps
-
Digital Stopwatch 0-60sec
-
LED Chaser
-
Alternating Flasher
-
Brightness of multiple displays control circuit
-
12 Volt Lamp Dimmer
-
PWM Motor/Light Controller
-
Bicycle back Safety Light
-
Temperature-controlled Fan
-
1.5 Hour Lamp Fader (Sunset Lamp)