A simple touch switch can be constructed using a single transistor.
Connect the collector of the transistor to the power supply with voltage about 9v or more. Connect the emitter to the load (in our case an led). Connect two wires, one to the collector and other to the base of transistor. The connections are made as below.
Connect the collector of the transistor to the power supply with voltage about 9v or more. Connect the emitter to the load (in our case an led). Connect two wires, one to the collector and other to the base of transistor. The connections are made as below.
when we touch the two terminals shown above, the current passes from the battery positive through our skin into the base of transistor turning the transistor on. thus the led glows when we touch the terminals acting as a touch switch.
will current through our body kill us?
usually people think that passing current through our body may kill us but to kill a human apart from current, voltage is also important. say we touch a wire carrying a current of 10Amps and 12volts then nothing will happen to us as atleast 100v is needed for us to get an electric shock. consider another wire having only 20mA but a voltage of 200v then this might kill a human on contact fro long time.
usually our body resistance is about 100k which is enough for the current to pass from the battery to the base to switch in the transistor.
This same design can be used to detech water level where one of the wires can be kept inside the water and the other at the level which is to be indicated. when water comes in contact with the wire it starts conducting current and the led glows.
a series resistor of about 330ohms can be added at the collector just to limit the cuurent going to the led.
here is a video of demonstrating the above concept.
u can add multiple such transistors to increse the sensitivity of this circuit.
