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
the working principle of 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|
|O||ON||0.3s … 3s|
|ON||O||1s … 10s|
|ON||ON||10s … 1.5min|
|O||O||1min … 10min|
|15 sec to 10 hours|
|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.