A Timer That Re-Triggers At Regular Intervals

  
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This circuit has an adjustable output timer that will re-trigger at regular intervals. The output period can be anything from a fraction of a second to half-an-hour or more - and it can be made to recur at regular intervals of anything from seconds to days and beyond. The output section is a simple Monostable Circuit. When Pin 6 of the Cmos 4001
A Timer That Re-Triggers At Regular Intervals - schematic

is taken high - the monostable triggers - and the relay energizes. It will remain energized for a period of time set by C1 & R3. With the values shown - R3 will provide output periods of up to about 30-minutes. However, you can choose component values to suit your requirements. For example, if you reduce R3 to 1meg - and C1 to 4. 7uF - the maximum output period is between 3 and 5 seconds. Owing to manufacturing tolerances - the precise length of the time period available depend on the characteristics of the actual components you`ve used. The Cmos 4060 is a 14-bit binary counter with a built-in oscillator. The oscillator consists of the two inverters connected to Pins 9, 10 & 11 - and its frequency is controlled by R7. The output from the oscillator is connected internally to the binary counter. While the oscillator is running - the IC counts the number of oscillations - and the state of the count is reflected in the output pins. By adjusting R7 - you can set the length of time it takes for any given output pin to go high. Connect that output to Pin 6 of the Cmos 4001 and - every time it goes high - it`ll trigger the monostable. Ideally C4 should be non-polarized - but a regular electrolytic will work - provided it doesn`t leak too badly in the reverse direction. Alternatively - you can simulate a non-polarized 10uF capacitor by connecting two 22uF capacitors back to back - as shown. Do not use the "on-board" relay to switch...



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