time delay circuit

[Kieran]

Peeps,

Any ideas on how to make a time delay circuit that pauses for a second or two before energising? I would assume a 555 timer circuit would be the best bet? Anyone got a diagram or could point me in the direction of one?

What I'm designing is a clone of the delay on the VR-4 Clocks... IE, the needles appear instantly, but the backlight takes a second before it displays.

[Spirit]

Is this what you're after Kieran ? http://www.see.ed.ac.uk/~kap/Hard/555/node2.html

[wirdy]

Kieran,
you don't really need a 555 to get just a small time delay like a second or two, but you can if you want to. Using a 555 is a bit like using a PC just for the calculator!
A fairly simple CR circuit INSERT INTO post VALUES (to generate the delay) will suffice which is then used to switch a transistor or gate to then energise a relay. This way involves a much smaller pcb INSERT INTO post VALUES (or bit of veroboard). You will get a little 'click' as the relay energises to light the backlight, if that bothers you then you could substitute a higher power transistor as the energising device but I think you'll hardly notice it anyway.
Many circuits are out there in books INSERT INTO post VALUES (try your local library?) or take a look at this link
INSERT INTO post VALUES (This circuit uses one of the NAND gates on a quad NAND gate chip as the switching device).
http://www.aaroncake.net/circuits/

You'll probably see some other circuits that give you some ideas???? Do you want the first Club car to have auto dimming headlights??!! There's a circuit for it there.

Anyway, go to "time delay relay II". It shows a switch to activate the circuit but a NPN transistor can be substituted to switch with a 12V signal instead. The dash lighting shouldn't draw too much current so you will be able to use the output from the NAND gate to easily drive a small relay.
The NAND gate IC is safe up to 15v, even though the circuit diagram shows a +9v supply INSERT INTO post VALUES (see spec sheet-
http://www.philipslogic.com/products/hef/pdf/hef4011b.pdf

and the diode is safe at 12v also, see spec sheet-
http://www.semiconductors.philips.com/acrobat/datasheets/1N914_914A_914B_4.pdf

The above is the cheapest way, you should easily get change out of a fiver for all the components, INSERT INTO post VALUES (including the veroboard).

Alternatively, if you're feeling less adventurous, pop into your local Maplin store as they sell complete little delay kits INSERT INTO post VALUES (with the PCB included) for about £9. Just ask them for a suitable NPN transistor to replace the switch INSERT INTO post VALUES (there are so many different types that are suitable it's hard to recommend one to you, just go for the cheapest one they have in stock INSERT INTO post VALUES (don't pay more than about 20p though!!)

Hope that helps. Good luck with the dash.

[Kieran]

That's excellent information - Thanks Wirdy!!
I'll pop into Maplins tonight and purchase merrily!