2 to 4 Seconds Timer?

I hope this is the correct place to post this as its my first post but having not done any component level hands on electronics for over 2 decades I have found myself struggling with some fairly basic concepts so any help would be gratefully recieved

I want a circuit that will when power is applied allow that power to pass through for about 2-4 seconds after which it will stop allowing the voltage to pass until the circuit is powered down and repowered again.

I have been trying some variations on 555 and transistor circuits but the component counts have grown and grown to the point where I am hoping there is a simpler method I either havent found or cant remember that I have overlooked

The load draws 200-300 milliamps so I was wondering if I could even just do this with a CR circuit or whether that would always leak some current through. The other possibility I was wondering about is whether its possible to place a CR circuit on the emitter of a transistor that was biased to switch on instantly, which would then bias the base over the CR time to switch it off after the 2-3 second or so time period

The motor I need to power takes the same kind of current as a dashboard light so thats what I have been using to try and prototype this. And all the circuit needs to do is just allow the 12v signal to pass for around 2-4 seconds after the engine starts then stop passing that voltage for as long as the car is running nothing more

So circuits involving 10-15 components "feel" far more complex than should be needed although I also accept that after not playing on this level for so long my "gut" might be flawed but I thought I would ask anyway on the offchance somebody else has already created a circuit to do a similar task

Thank you in advance for any help/suggestions offered

Mike

PAC TR-7

Check out Feature #12, I think this will do what you are looking for.

Yes it looks like it would do that but I checked the price and its around $30 dollars worth of hardware to replace around $5 worth of normal components

At the moment I'm looking at a toss up between a 555 timer or a monostable transistor circuit driving a drive transistor to power the load and was really just wondering if there was a simpler cheaper approach that was lower tech rather than higher tech that would do the same task.

But thank you for suggesting that module, I have to admit its something I have never even seen before and it certainly looks worth reading up on incase I have another project later on that would justify the cost of one of those as it looks pretty cool and versatile

So you want a simple monostable.... It shuts off after a delay (from power on).

It should be easy with a 555, and it should be easy with and RC-transistor/FET (and diode?) combo...
But I write should because (1) I never find the circuits when I want them, and (2), when I start figuring out my own, it often gets real convoluted (until I figure out I'm totally wrong anyhow!).

With (2), nothing has changed.
With (1), I'd be googling since I still haven't bothered recovering my old lost data.


PS - from electronicspoint.com - need-help-3-second-delay-circuit-t234437, the last circuit(KMoffett's) namely:


Similar to my thoughts...
Change the supply to 12V (no change)
C1 is initially a short so the FET turns on.
C1 charges so the FET's gate (like transistor base) drops below the required (say) 3V to 5V between Gate and Source (ground) that turn the FET on.
R1 is to discharge the cap between power cycles (off to on).
D1 is to prevent the FET's Gate going -ve due to the charged cap (and power removal).


PPS - components not critical, though I'd use a IN400x for the relay's D2 (not the 1N4148), and may as well use the same for D1.
R2 x C1 set the "on" time.
R1 x C1 is the reset time (minimum "off" time required for another power-on 3-second-on. Else R1 could be omitted if SWitch is SPDT with "off" to GND - but then make sure D1 is fitted.