Touch switch based on timer. Scheme, description

Touch switch based on timer. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Radio amateur designer

A cheap and reliable touch switch can be built using the 555 timer IC, says Berlin, a technical consultant in Wilmington, Delaware. The basic switch circuit is obtained by standardly turning on the timer as a standby multivibrator and connecting the reset input (pin 4) to a power source, and the start input (pin 2) to the sensor plate.

This plate can be copper or aluminum. Momentarily touching it with your finger causes the timer output to go high for 1,1 times the RC time constant. If you keep your finger on the plate, the output level remains high. A time constant of about 1 s is usually sufficient. To work with self-locking, you should generally remove the timing resistor and connect the normally open contacts of the button between the timer reset input and ground. Now touching the plate will cause the timer to self-lock for an indefinite amount of time until the reset button is pressed.

To make an on/off touch switch, a 7473 type JK flip-flop should be added to the main circuit. The output of the circuit is connected to the trigger clock input, the J and K inputs of the trigger are connected to a 5V power supply, and the Q output is connected to the load. In this circuit, one touch of the plate will cause the load to be connected, and the second touch will cause the load to be disconnected. If you add a transistor key, you can control household electrical appliances.

Literature

Electronics 12, 1977

Publication: N. Bolshakov, rf.atnn.ru

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