Vermes
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This construction of a relay with switching delay is a simple design which can be easily performed by beginners who want to create such a thing for controlling the gateway from home. In this case, the gateway uses electromagnet and it has to be opened by a key. Presented here construction is based on the fact that the relay switches the electromagnet for about 15 seconds, 15 seconds after pressing the button.
The design was made on an 8-pin microcontroller, but it can be performed on s NE555 as well. One of the advantages of the microcontroller is that you can easily make a state control based on LEDs and the delay time control does not have to be made on potentiometers.
Resistor R2 is an additional resistor that prevents the button from “pressing itself” what could be caused by the fact that the cable of this button is next to the beams of alternating voltages and responds to disturbances. Addition of the R2 eliminated the problem.
Link to original thread (useful attachment) - Przekaźnik z opóźnieniem załączania