A Repeating Timer Circuit No.7


Posted on Feb 6, 2014

This timer is based on a simple Monostable Circuit. The length of time the relay remains energized - the ON period - is controlled by the values of R3 & C2. And the length of time the relay remains de-energized - the OFF period - is controlled by the values of R4 & C3. With the component values shown - periods of up to 30 minutes are available. T


A Repeating Timer Circuit No.7
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he length of time the relay remains energized is controlled by the values of R3 & C2. And the length of the time the relay remains de-energized is controlled by the values of R4 & C3. Owing to manufacturing tolerances - the precise length of the time periods available depends on the characteristics of the actual components you`ve used. You can choose component values that suit your own requirements. You should get about 70 seconds for every 1Meg/100uF. So 4M7 & 100uF will give about 6 minutes. And 4M7 & 1000uF will give about an hour. If your time periods don`t need to be too precise - and more-or-less is close enough - you can replace the pots with fixed resistors. Do not use the "on-board" relay to switch mains voltage. The board`s layout does not offer sufficient isolation between the relay contacts and the low-voltage components. If you want to switch mains voltage - mount a suitably rated relay somewhere safe - Away From The Board. I`ve used a SPCO/SPDT relay - but you can use a multi-pole relay if it suits your application. The timer is designed for a 12-volt power supply. However - it will work at anything from 5 to 15-volts. All you need do is select a relay to suit your supply voltage. The Support Material for this circuit includes a step-by-step guide to the construction of the circuit-board - a parts list - a detailed circuit description - and more.




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