Home > Circuits > Touch Switch

Touch Switch

Simple touch switch circuit, works on the fact skin has a resistance
By 26/10/10 [Last Edited by Joseph 14/08/11]
BOOKMARK
LOGIN
REGISTER
The circuit uses skin resistance (between a few hundred kilo-ohms and a few mega-ohms) to activate the relay. Transistors are used to amplify the and drive the relay from the tiny current across the skin. An LED indicates when the relay is energised.

Schematics

Parts

Component Name/Description Quantity
R1 10K 1/3W 5% 1
R2 4.7K 1/3W 5% 1
R3 1K 1/3W 5% 1
D1 TIL209 (0.125 Red) 1
D2 1N4148 1
RL1 6/12V Coil, 185 Ohms or more 1
TR1 BC109C 1
TR2 BC179 1
Touch Contacts 2
Wire N/A

Notes

This is not a latching switch, so as soon as the finger is removed from the two contacts, the circuit will switch off. You could connect the relay contacts to something such as a Microcontroller, or to logic circuits to perform the latching.

Author

R.A Penfold (From 30 Solderless Breadboard Projects - Book 1)