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Touch Switch PDF
LEFT: Light an LED with current flowing through your finger! You'd need 10 mA. This is a potentially fatal current but impossible at 5 volts.
MIDDLE: Use a bipolar transistor as a current amplifier. The BC182L amplifies the Base current about 200 to 300 times. The LED lights, perhaps dimly. You might need to wet your finger.
RIGHT: Use two transistors multiplying the current by up to 300 x 300 = 90 000. This works and it's posssibly too sensitive.
Build this circuit. Use your fingers to bridge the gap as shown. The LED might light dimly. If you have sweaty fingers, it might be brighter.
This uses two transistors so the current multiplying effect is much greater. So great in fact that just touching the base connection without completing the circuit is enough to light the LED. Your body is acting as an antenna and picking up all the electrical noise in the room. This is sufficient to light the LED.
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