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Soft ON/OFF switch

- Designed by Naveen P N

Modern electronic equipment incorporate “push-to-on-push-to-off” switches that do not make the clicking noise as with old equipment. An example of this is the power button on a ATX computer cabinet. Here is a circuit that does the same. It can be used to turn on/off any electronic/electrical equipment that operates on any range of voltages.

When the “ON/OFF” button is pressed once, the equipment goes on and stays on. It goes off when the button is pressed again. The circuit is straight forward. It uses a JK CMOS FlipFlop to with its JK terminals tied high to achieve the toggling action. The clock is provided by the push button used for on/off action. The resistor and the capacitor near the on/off switch debounces the contacts.
Note that when the circuit is switched on, the relay may land in a on or off state. It can be brought to the off state by pressing the RESET button.

Care should be taken that the relay’s current does not exceed 100mA.
Since the IC is CMOS, it can be operated from 3V to 15V, but in this circuit it is operated at 9V for a 9V relay. The relay circuit needs to be modified for other operating voltages.

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