Transistor circuit for alarm LEDs

[dryden_burton]

Im looking to install a Blue LED in each headlight and tail light and connect them to the alarm led via a transistor. Anybody have a schematic? and a suggestion on the transistor to use? thanks.

 

[Reloadron]

What alarm? Explain in some detail exactly what you are talking about. What exactly are you trying to do and why?

Ron

 

[dryden_burton]

Basically want to amplify the power from the flashing LED on the aftermarket alarm, to flash four LEDs mounted in the head and tail lights to give a better warning to theives.

 

[Reloadron]

Basically want to amplify the power from the flashing LED on the aftermarket alarm, to flash four LEDs mounted in the head and tail lights to give a better warning to theives.

Then I would be thinking about using a 555 timer configured in an astable mode driving a transistor which in turn drives your LEDs. The existing alarm system can likely be used to trigger (power) the timer circuit.

Ron

 

[dryden_burton]

The led also serves as a status indicator (flashes different) so i would like to use the existing LED wire to control the flash rate of the LEDs instead of using the timer to flash the LEDs.

 

[Reloadron]

OK, so you have an existing LED that is part of the existing alarm system and want four additional LEDs to flash and mimic what you already have?

If that is true you may be able to place maybe an opto coupler in parallel with the existing LED and let that drive the other LEDs using it as a slave. Another option might be to have the signal driving the existing LED drive a transistor slaved to it and the transistor drive the remaining LEDs.

Without seeing exactly what you have it is hard to suggest how to expand upon it.

Ron

 

[shokjok]

How bright are these blue LEDs? I doubt much that small flashing lights will detract thieves from their intentions. Look at flashing red LEDs currently in some vehicles - they are no deterrent. Thieves know that these can be mimicked, no alarm exists.

 

[dryden_burton]

shokjok better than nothing i have an alarm hense the ultra bright blue that aftermarket alarms have, red is stock no alarm. plus the leds light up the whole light housing at night looks cool.

"OK, so you have an existing LED that is part of the existing alarm system and want four additional LEDs to flash and mimic what you already have?"

Exactly.

"Another option might be to have the signal driving the existing LED drive a transistor slaved to it and the transistor drive the remaining LEDs."

Thats what i was thinking, what about a darlington pair? Any suggestions on transistors, I suspect the alarm output is 20mA at around 3V.

 

[Reloadron]

shokjok better than nothing i have an alarm hense the ultra bright blue that aftermarket alarms have, red is stock no alarm. plus the leds light up the whole light housing at night looks cool.

"OK, so you have an existing LED that is part of the existing alarm system and want four additional LEDs to flash and mimic what you already have?"

Exactly.

"Another option might be to have the signal driving the existing LED drive a transistor slaved to it and the transistor drive the remaining LEDs."

Thats what i was thinking, what about a darlington pair? Any suggestions on transistors, I suspect the alarm output is 20mA at around 3V.

This is where it is hard to move forward without knowing what is there and what the added LEDs would be?

The existing LED is likely a LED with some series resistor fed by some voltage. The "some" needs to be a known. Next the added LEDs need to also be a known. Till then we can speculate to no end.

A simple little 2N2222 can drive 100 mA easy sans any darlington pair configuration and depending on the setup a basic logic level MOSFET could drive a few dozen LEDs likely. It's just the damn pesky unknowns that haunt.

Ron

 

[dryden_burton]

The existing LED has 12.5 volts on each leg. to make the LED flash the negative sige drops to 10 volts.