Here is the smallest circuit that is both interesting and very responsive. It is a very reliable Metal–Oxide–Semiconductor Field-Effect Transistor (MOSFET) based Touch Sensitive Switch.
In this circuit (named as Magic of MOSFET – MOM) I have made a Simple Touch Sensitive Switch using single 2N7000 MOSFET to switch ON and OFF a 3V (white) LED that can be replaced (along with the 330ohm resistor) by a 5 Volt Micro Relay to Turn On/Off 220V load.
Operation of touch activated switch circuit:
The Gate Terminal (G) of the MOSFET Transistor is insulated from the Drain (D) and Source (S), so that it can hold the charge and act like a small capacitor.
To Turn ON the LED using touch switch just place your finger across Gate (G) and the Positive Terminal (A), which will charge the Gate through the finger and the circuit will turn/remain ON as the Gate Terminal will hold the charge. Now to Turn OFF the LED you just have to place a finger across Gate and Source Terminal of MOSFET (marked B) which will discharge the Gate through the finger, and the MOSFET (2N7000) will go into OFF state – turning OFF the LED (or Relay).
For AC Load:
Now to control the AC Load you just have to replace the LED and the resistor with a 5V micro relay. Connect your 220V Load / Lamp to the N/O of the Relay.
- 2N7000 (MOSFET)
- 3V White LED
- One Small Empty Matchbox
- 9V Battery
- 9V Battery Connector
- Small 1inchx 1inch PCB
- 20cm wires
- Soldering Iron, Soldering Wire, Wax
Cost of Project: INR 30/- (Including Battery)