0.3 Second to 10 Hours Timer Relay with 4541 IC

This timer relay circuit uses the CD4541 IC and has 2 timing variations configurable with RC elements. The specifications of this timer are:

  • modes of operation: astable/monostable
  • the output has a 6A/250V relay with NC/NO contacts
  • LED signals exiting the timing state
  • manual programming done with a DIP-switch
  • 12V voltage operation

Schematic of the Timer Relay Circuit

4541 timer relay circuit schematic

working principle of the timer

Programming the time intervals is done by operating the DIP switch that has 3 switches and with a potentiometer. Depending on the position of SW1 1 and 2 contacts, the timer can be configurated for the 4 time ranges, as shown in tables:

0.3 sec to 10 minutes
SW1 time interval
1 2
O ON 0.3s … 3s
ON O 1s … 10s
ON ON 10s … 1.5min
O O 1min … 10min
15 sec to 10 hours
SW1 time interval
1 2
O ON 15s … 3min
ON O 1min … 10min
ON ON 10min … 1.5h
O O 1h … 10h

Use the potentiometer for setting the timing period within these intervals.

For the 0.3 second to 10 minutes timer version the potentiometer is 100kΩ, R1 = 9.1kΩ, R2 = 910kΩ, R3 = 220kkΩ and C1 = 100µF.

For the 15 seconds to 10 hours timer version the potentiometer is 1MΩ, R1 = 51kΩ, R2 = 1.2MΩ, R3 = 1.2MΩ and C1 = 1µF.

The operating mode is selected with the third contact of SW1:

  • ON position = monostable
  • O position = astable

In order to start the timining you have 2 possibilities: you either connect the START point to ground GND and in this case the timer starts when you connect it to the voltage supply or you can place a switch to start it.

All the resistors are 0.25W and C1 must have a good stability over time.


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