Repeating Timer No.8

This circuit energizes the relay repeatedly – at regular intervals. The length of the intervals depends on the setting of R4 – and the output pin to which the “Range” wire is connected. With the range wire connected to pin 3 – intervals of up to 24-hours are available. If you need longer than 24-hours – increase the value of C3.

The length of time the relay remains energized – depends on the values of C2 & R8. With the values shown – it will remain energized for up to about six minutes. If you increase the value of R8 to 5 Meg – periods of up to half-an-hour are possible. If you also increase the value of C2 to 1000uF – the relay will remain energized for up to an hour.

I used a 12-volt supply to power the prototype. But the circuit will work at anything from 5v to 15v. You just need to select a relay – with a coil that suits the voltage you want to use.

Schematic Diagram

The Cmos 4060

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 R4. 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 state of the output pins.

By adjusting R4 – you can set the length of time it will take for any given output pin to go high. If you connect the “Range” wire to that output pin – every time it goes high – the relay will energize for a period of time – the length of which is set by the values of C2 & R8.

The Support Material for this timer includes a detailed circuit description – a parts list – a step-by-step guide to construction – and more. Ideally C3 should be non-polarized – but a regular electrolytic will work if 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. Because 10uF non-polarized capacitors are not widely available – I’ve used two regular 22uF capacitors in the prototype.

Important

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.

Stripboard layout

 

Since the delay between relay outputs can last for hours – or even days – using “trial and error” to set-up the timer would be very tedious. A better solution is to use the Setup Table provided – and simply calculate the time required for pin 7 to go high.

Setup Tables

For example – if you want the relay to energize at intervals of four hours – the Range Table tells you that you can use the output at pin 1 (two to six hours). Four hours is 4 x 60 x 60 = 14 400 seconds. So you need pin 1 to go high after 14 400 seconds.

According to the Setup Table – pin 1 takes 256 times longer than pin 7 – to go high. In other words – if you adjust R4 – so that the yellow LED lights after (14 400 ÷ 256) about 56 seconds – the relay will energize after about four hours.

Although R1, R2 and the two LEDs help with the setup – they are not necessary to the operation of the timer. You can leave them out if you wish. If you want the LEDs to glow brighter – use brighter LEDs. Don’t be tempted to reduce the values of the series resistors – especially R2. If you reduce its value too far – the 4060’s counter may not advance reliably.

Copyright Ron J

2 thoughts on “Repeating Timer No.8

  1. sajad

    i WANT TO SEND THESE DIGITAL VALUES OF TEMPERATURE SENSOR TO
    ANOTHER MICRO CONTROLLER USING INFRARED MADUALS AND LM35 SENSOR. hOW DO i DO THAT.WHAT IS CIRCUIT DIAGRAM . WHAT WOULD BE THE CODE FOR SENDING THOSE DIGITAL VALUES OF THE TEMPERATURE SENSOR SERIALLY TO THE TRANSMITTER AND FORM THERE TO THE ANOTHER MICROCONTROLLER

  2. Ron Sharpe

    Just the circuit I was looking for!  I want to have a “Garage Door Open” alert.  I will use the relay N.O. contacts in your circuit to ‘press’ a wireless doorbell button TX (say once every half hour) to alert me that the garage door is still open.  I will use a magnetic ‘reed relay’ on the track of my garage door, to supply 12 volts to your circuit when the door is open, to start the 30 minutes timer.  I will adjust the ‘relay on’ time period to be about 0.5 seconds to simulate the ‘doorbell button’ being pressed.

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