Touch Based LED Lights Physics Investigatory Minor Project and Model

The human body conducts electricity weakly because body fluids contain dissolved salts, and it also acts like one plate of a small capacitor. A touch circuit uses one of these effects. In the simplest designs, a finger bridges two metal contacts and lets a very small current flow; this is far too weak to light an LED, so it is fed to a transistor. Often two transistors are joined as a Darlington pair, where the current gain of the first is multiplied by that of the second, giving gains in the thousands. Other designs use a touch-sensing chip that detects the extra capacitance a finger adds. Either way, a tiny input controls a much larger output current, which lights the LEDs. An LED is a diode that gives out light only when forward biased, so it must be connected the right way round. Touch-sensitive switchboards in some modern Indian homes and the screen of a smartphone work on these ideas.