sm

I'm looking for some red LEDs that can take 12v and blink as well. Does anybody know where I can buy them?

Thanks!

IceShark

Simpson, what are you trying to do?

If you want to put them into the exterior flashers you have two problems.

LEDs don't work on light output very well with the lens and reflectors designed for a regular filament bulb. Trust me on this, I had LedTronics (a big manufacturer that probably sent me a salted sample of the best production bulbs) send me some samples and I tested them.

Second, they cost a small fortune at this time. You will spend $25 to $35 per good quality bulb replacement at retail for an underperforming light.

Trust me, you will not be a happy camper if you go this route. The new manufactured items designed for LED and bought in huge bulk are nice. Retrofit SUCKS, bigtime.

Flashing a LED is no problem. They actually do it much better than a filament bulb.

What happened, did you get a cash bonus that is burning a hole in your pocket?

sm

Dan,

I was thinking of a project on a much smaller scale. Since my car's factory alarm is old and probably inoperable, I was thinking of installing a LED next to the switches in front of the shifter. Then connect the LED to a 12v source and an on/off switch and have a "deterrent" device Or I was thinking of hooking that LED up to a kill switch...

sm

Ha! Don't I wish. Now that my gf's car needs attention too, a bonus would be nice! And if I did, I would get a real alarm

IceShark

Ahh, there are those available and for fairly cheap. Fake alarm lights. I think they are under 15 bucks and come as a complete package. Search the web and see what other Rennlisters have to say on where to buy them.

951Tom

I did this to my old GTI. I wired it up to the emergency brake light switch. So whenever the emergency brake was on, the light would blink. This way I didn't have to worry about manually flipping a switch each time I got in and out of the car.

Ag951

Crutchfield used to sell (might still sell) a fake alarm light for $15.
Otherwise try radio shack. The LEDs won't blink (they're just diodes). You'll need to build a blink circuit. I'd suggest dual 555 timers (or a 556 dual timer chip).
Radio shack has a book on 555 timers (at least they used to), that told you what to do and how to calculate the resistor values, etc. to get the right frequency on your square wave.

Chris_924s

IC 555 timer, a 12V to 3V (or 3.3v, I cant remember) stepdown transformer and you are in business. If you can breadboard a little bit you can do this rather nicely for about 2 bucks in parts, and use any switch to trigger it that you may want.

and It wont suck the life out your battery. I'ts beginners electronics. Look on the net for 'LED FLASHERS' or IC 555 timers and you'll get the idea, along with somecircuit diagrams.

Ag951

I wouldn't run it off the car battery. Just get a 3.3V LED from radio shack, build a circuit, and run it of a $1.29 watch battery: no wires, no transformer.
Prototype it on a breadboard, but I'd suggest a PCB for the real deal, due to size issues.

944Play

Radio Shack sells 5mm LEDs with internal blinking circuitry. Just step down the voltage with resistors, or a regulator if you want to get fancy.

My $50 RKE system came with a LED that blinks when "armed."

jason952

I got one at performance products, works well.

Jason

sm

Can you tell me how to do that? I know V=IR, but would a resistor step down the voltage, or just limit the current?

I would like to go off the car's 12v circuit, as that allows for more options in terms of tying the LED to a switch, such as the E-brake (good idea by the way)

Thanks!

MartinT

To step down the voltage using a resistor, you are creating a potential divider.

I is constant so V is directly proportional to R.

Say you had a 200 ohm and a 100 ohm resistor is series with a batter you would get 2/3 of the voltage across the 200 ohm resistor. And 1/3 of the voltage across the 100 ohm.

Hope that helps

Ag951

If you're stepping down from a 12V car battery to 5 volts, you'd want to create a circuit like so
(Nice crude drawing, but you get the idea).
R1 would be 7/12ths of the total R1+R2, and R2 would be the other 5/12ths. That would give a 7V drop from the positive terminal to the branch, and 5V from the branch to the negative.
However...this is a really bad idea with a car battery. A car battery, with its dozens of amps, could easily fry this circuit.
The best idea is to get a watch battery for $1.29 at radio shack. An LED requires minimal current, so a decent watch battery would last you months if not years.

If you get one of those LEDs with he built in timer circuit, and a battery, all you need to do is put them in a little plastic box with some double sided tape on the back.

sm

Sorry for my repeated questions, but I'm electrically-ignant

Radio Shack has a Blinking LED whose specs are:

20 mA (max)
Typical voltage of 2.8V (max of 3.8V)

So what size resistor do I need to make it work with our 12v systems?

Thanks!