A microampere dc current through your fingers can control heavy-duty loads such as home appliances, motors, and heaters up to 8,800 W.

The circuit consists of a bistable touch-controlled multivibrator that drives a TRIAC through a unijunction transistor (UJ T) and an isolating transformer. The TRIAC, a TIC226-B, is rated for loads up to 800 W (8 A, 117 V) and must be mounted on a heatsink.

Wires to the touch plates can be as long as you want, and you can place it some distance from the circuit to be controlled. As the control line operates with a low voltage and low current, no special care needs to be taken with the connection.

A schematic diagram of the Full-Wave Touch Switch for AC Loads is given in Fig. 1.

 

Figure 1 – Schematic diagram of the Touch Switch
Figure 1 – Schematic diagram of the Touch Switch

 

Make sure that the ac high current line isn't connected to the board and that the wire used is appropriate for this task. The TRIAC must be mounted on a large heatsink.

T2 is a pulse transformer (1:1) as used in many circuits to trigger SCRs and TRIACs. X1 and X2 are touch switches made with two small metal plates that are simultaneously touched by the fingers. R3 is adjusted to the maximum power of the load when the circuit is on.

IC1 4093 CMOS integrated circuit

IC2 7812 voltage regulator IC

TRIAC TIC226-B, Texas Instruments

Q1 2N2646 unijunction transistor

D1, D2 1N4002 or equivalent silicon rectifiers

S1 SPST toggle or slide switch

X1, X2 Touch sensor (see text)

F1 10 A fuse and holder

T1 12.6 V, GT, 300 to 500 mA transformer

T2 1:1 pulse transformer

R1, R2 10,000,000 ohm, 1/4 W, 5% resistors

R3 100,000 ohm trimmer potentiometer

R4 10,000 ohm, 1/4 W, 5% resistor

C1 1,000 µF, 25 WVDC electrolytic capacitor

C2 0.047 µF ceramic or metal film capacitor

C3 100 µF, 16 WVDC electrolytic capacitor

 

 

Datasheets


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