My understanding from the attachement in post #1 was he wanted the relay coil to be de energised 40 seconds after the control signal went to 12 volts and that he wanted it energised again as soon as the control signal went low. I don't see why he could not use it the way you have designed it just by swapping the NO amd NC contacts on the relay.
Yes Les, I want the relay to be turned off 40 seconds after the trigger signal is at +12 volts and to turn it back on as soon as the trigger signal goes low. I gave the circuit with a triac just as example.Hi milkoni,
In post #1 you say that you want the relay to be turned off 40 seconds after the trigger signal is at +12 volts and foor it to turn back on as soon as the trigger signal goes low. The triac timer will turn the relay on after the delay and turm it off when the power is removed. (Which is the opposite of what you requested.) You may be able to get round this by swapping over the NC and NO contacts on the relay. For my circuit to work that way would require two less transistors.
Mike, I like this circuit too, but there is some delay after the signal +12V is off.Here is my hack at it. I am assuming that S2 comes from a contact closure. The circuit has more-or-less symmetrical delays on both rising and falling edges of S2. Note I(L1) relative to V(s2) in the plots.
The delay is ≈R1*C1, so you could use a 1meg pot for R1 or change C1 as needed. If you want asymmetric delays (separately adjustable) , then you can replace R1 with two pots and steering diodes. M1 is old-school NMOS like a IRF510 which has a Vth of ~4V (not logic-level like more modern ones). The relay is almost any 12Vdc relay, even the 85Ω automotive sugar-cube type would work.
View attachment 105094
I have attached the LTSpice file so you can play with it...
Yes Mike,Yes, that was the error in my understanding of your requirements that Les pointed out to me, which I corrected in post #10.