555 or one shot

A 555 in monostable configuration. Described about 1/3 from top on this page:
https://www.electronics-tutorials.ws/waveforms/555_timer.html

Other ways to make monostable multivibrators is shown here:
https://www.electronics-tutorials.ws/waveforms/monostable.html

 

Alternatively buy a ready made module complete with relay for a couple of dollars from Ebay.

 

Ebay...look for 555 monostable relay module

 

See attached circuit for a very simple timer.
How it works:
R1 and R2 serve to charge C1. Because C1 cannot charge instantaneously, R3 is pulled up to the +12V rail. turning on Q1 and Q2. Q1 and hence Q2 will turn off when as C1 charges, the voltage at the top of R3 reduces to about 4V.
As well as the time constant of the C1 R3 and R1 combination, the ratio of R1 and R3 determines the point at which Q1 turns off therefore the on period may adjusted by making R1 bigger or smaller.
The circuit was simulated using Simetrix and produced an on period of about 1.5 seconds. The simulation does not take account of the leakage current in C1 thus some adjustment may be need to its value to achieve the required period.

 

Forgot to mention, LED goes in collector of Q3.

 

What's difficult about a couple of transistors a few resistors and a capacitor.

 

Like I said above....Ebay.
Obviously you didn't read that.

 

That's correct.
Normally power is applied to the 555 unit, then when required, a trigger pulse is given which times out the 555 for the set time.
Which unit did you purchase?

 

The thing is, you don't learn anything just buying bits off ebay. I thought that was the point of this forum or did you miss that?

 

Well actually the Op said they wanted the "best/most simple way to achieve this" and so the suggestion.

Doesn't appear to need a separate trigger as there is no input for such, however the one you are looking at appears to be a "delay-on" arrangement.
To me that means it will delay the turn on for the set time period and then switch the output on.

 

Try this one...a lot cheaper also although you might have to wait a bit for delivery.

Notice the instructions are there also, hope this helps you out...cheers

Only drama I can see would be that the unit is for 0 to 60 seconds and it might be a bit fiddley getting 1 or 2 seconds. you could in that instance replace the on-board potentiometer with a 15 turn unit of the same resistance value. These also come on Ebay for a few cents each.

https://www.ebay.com.au/itm/DC12V-0...801139?hash=item41cbb96cf3:g:6M0AAOSwI0RZe~hl

 

Yes, I did see that.