I don't think that circuit will work since, if a real 555 TRIG input is held low, I believe the output will stay high.The PNP transistor discharges the capacitor when the switch is opened (the timer is turned off. It is important to discharge the cap so you get the same 5 seconds of delay after each switch throw that powers up the 555. The 555 can directly drive many relay coils if you have a 5 or 12 v coil under 200mA.
View attachment 250668
I love the CD4093 chip! it's my all-time favorite part in fact.Below is the LTspice simulation of a circuit using one CD4093 quad 2-input Schmitt-trigger package, and an N-MOSFET driver for the relay:
The relay turns on (yellow trace) about 2s after the power turns on (green trace) and turns off about 5s after that.
The 555 triggers on power up in mono-mode. It is a challenge to prevent the triggering on startup.I don't think that circuit will work since, if a real 555 TRIG input is held low, I believe the output will stay high.
Closing the switch near Vcc causes the pulses in the image above.What generated that displayed output?
Yes.Could the circuit be simplified if I did not require the 2 sec delay after power is applied? ie: Apply Power | turn on relay for 5 secs | turn off relay until power removed & applied again.
why build a circuit.Hi all,
I require a simple cct that will activate a small relay for 5 secs 2 secs after power is applied to the circuit. Maybe a 555?
If you can't, an added transistor delay will provide that (below):Does not have the ON delay but I believe I can live without that.
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