Reducing 12 volts DC to 1.5 volts

[dave#3]

I know there's a few electrickery geniuses here so I was hoping one of you might be able to help. I'm trying to make up some warning lights for the mutant (an ignition "on" light, a neutral light and an oil pressure warning light) and was hoping to use LEDs. I need to supply about 1.5 volts to the positive side of the LEDs and use the switches (ignition, neutral and oil pressure) to complete the circuit to earth, so .....

I believe I can reduce 12 volts to 1.5 volts using a big-arsed resistor (I guess ohms law will help me calculate exactly which one) and I've read about using a zenner diode (presumably reversed???) as a voltage regulator, but if any of you geniuses have a simple solution or can confirm or deny the usefulness of either of these solutions I'd be very appreciative.

Cheers,

Dave

[Rossi]

The easiest & cheapest solution is to use 12V LED's

[dave#3]

The easiest & cheapest solution is to use 12V LED's

Everywhere I looked the 12 volt ones were clusters in series and far too big for my needs ... but if they're available I'd be happy to get some. Any ideas where I'd get some from?

[mick_dundee]

Dunno about NSw but down here I would reckon Jaycar would be the go, sus it out www.jaycar.com.au no doubt.

[Ratmick]

LM317K or T three-terminal regulator. There'd be bugger-all current so you wouldn't need a heatsink.

Even better, use one of these in a small plastic box: http://www.dse.com.au/cgi-bin/dse.storefront/4ab766cb02212edc273fc0a87e01069f/Product/View/K3592

Mick

[Rossi]

Even cheaper

http://www.dse.com.au/cgi-bin/dse.store ... View/P8130

[6maniac]

Rough guide for a 2volt 20mA LED @ 12 volts = 500 ohm resistor.

Have soldering iron - can travel.

[ijuschill]

try these guys http://www.ledshoponline.com/ for the leds
also http://www.unique-leds.com/

[dave#3]

Cheers guys. The lamps Rossi linked to look perfect, I'll just have to find someone that's got them in stock.

Thanks heaps.

[mike-s]

well there are two things to look into, one is using a driver circuit to provide a higher rate of flashing for a rated LED/cluster, which is something like this or this, which is handy for visibility in the daytime.

To stick to the more "traditional" methods and just using a higher brightness LED you may want to find a LEd that you want and then use a led calculator such as this or this. For a bit of a tutorial on what your calculating, look here.

[dave#3]

Well I ended up finding some 12v LEDs at Jaycar (they're only new and weren't available a month or two ago when I bought the regular ones). The bad news is they're all red, but I got a flashing one that I'll use for oil pressure warning and regular red ones that I'll use for neutral and ignition. Thanks for all your help guys! I love youse

[6maniac]

Was in Jaycar this morning and saw 12volt green and red LED's with chrome bezel.

Cat. No. SL2644 - red
Cat. No. SL2645 - green

Both $3.65 ea

[dave#3]

Cheers mate, I might chase down a couple of them.

[mike-s]

perhaps look into a voltage regulation circuit of some sort to make sure they don't get over-volted?

just a suggestion that is.