In this tutorial, we are making a simple touch switch circuit project.
It is used to activate relays instead of LEDs and resistors so that you
can connect required loads or electronic devices to them and operate
through this circuit. This circuit is very sensitive because we use two
transistors that work as Darlington pairs.
Circuit Diagram & Working Explanation
Two transistors are used as a Darlington pair. The
first transistor first amplifies the gain, and then further amplifies
and multiplies by the second transistor, so we get a very high gain.
Because of this high gain, the circuit is sensitive to even the very
small amount of current that passes through our skin and activates the
LED. The circuit can work at 6.9 or 12 volts. Use 330Ω instead of Rx
when using 6V, and use 390Ω or 470Ω when using 9V or 12V, respectively.
If you plan to use a relay in the position of the LED and resistor, use a
relay with the same value as the input voltage. A 200KΩ variable
resistor is used to adjust the sensitivity of the circuit.
When you touch the contacts of the circuit, a very small current starts
to pass through our skin, thus completing the circuit, so that the
transistor (Darlington pair) is activated and the LED lights up.
