A circuit that turnes on the car LED above a desired voltage.

Thread Starter

ExError

Joined May 26, 2024
5
Hi! I need some help with a project. I want to make some custom LED tail lights for a friend’s car as a gift. He has a MK5 VW Golf.
The problem is that his tail lights use a single filament lightbulb for the brake and they are being used as running lights also. When the brake is pressed the light intensifies.

What I want to figure out is how I could make the brake LED stay off if the brake is not pressed. Is the light intensified by raising the voltage when the brake pedal is pressed? If so how can I keep the circuit off so it only lets the current flow after a set voltage?

Thanks in advance!
 

Alec_t

Joined Sep 17, 2013
14,398
Welcome to AAC!
In most jurisdictions there are strict rules concerning vehicle lights, so what you propose may be illegal. Have you checked?
Light intensity these days is controlled by a mirocontroller in the vehicle, using pulse-width modulation. Messing with that could cause expensive damage.
 

Thread Starter

ExError

Joined May 26, 2024
5
Well he plans to use the car for car shows in the future. Though in my country is pretty permisive in that regard. As long as the light is visible it should be fine. The circuit I use for the lights is safe, it uses 3W LEDs and are always used with LED Power Drivers. I even tested them for 12 hours at 14V to make sure they don’t heat up. They stay at ~50 C degrees which is great.
 

Thread Starter

ExError

Joined May 26, 2024
5
Welcome to AAC!
In most jurisdictions there are strict rules concerning vehicle lights, so what you propose may be illegal. Have you checked?
Light intensity these days is controlled by a mirocontroller in the vehicle, using pulse-width modulation. Messing with that could cause expensive damage.
Also, I checked if the car’s CANBUS would mess with the LED’s or even the opposite way. The only thing that the car will not like is the turning signals. I managed to solve the problem with the power drivers and a power resistor wired in paralel wit the circuit. After many tests it is safe.
 

Thread Starter

ExError

Joined May 26, 2024
5
The light needs to stay on for the daylight running light function.
They have another bulb for that. Basically they have a bulb for daylight running function, a bulb for the break that acts as daylight as well (it is made so in order to complete the circle design) so the tail will continue to have a daylight bulb
 

Hymie

Joined Mar 30, 2018
1,293
My understanding of these lamps that are combined running and brake lights is that the lamp contains two elements, one low power and another higher power. If this is the case there should be two supply wires to the lamp (and possibly a common 0V return wire – if not using the vehicle chassis for the return).

So you would need to make two led arrays (for each lamp), with the brake array brighter than the running led.
 

Thread Starter

ExError

Joined May 26, 2024
5
My understanding of these lamps that are combined running and brake lights is that the lamp contains two elements, one low power and another higher power. If this is the case there should be two supply wires to the lamp (and possibly a common 0V return wire – if not using the vehicle chassis for the return).

So you would need to make two led arrays (for each lamp), with the brake array brighter than the running led.
Their wiring is like this:
1 “-“ wire which is common for every bulb
1 “+” for the daylight
1 “+” for the brake which acts as a daylight
1 “+” for the turning signal
So I will have to work on the brake and - wire. If the brake bulb would have been a double fillament one, it would have been much easier. But since it has only one, well I need to come up with a way to restrict anything that is under a certain voltage.

The question is: how can I make the bulb only turn on after let’s say 13V?
 

BobTPH

Joined Jun 5, 2013
9,255
All you need to do is light different sets of LEDs with each of those three wires. You use a diode between the + and the LED(s) if any should be on with more than one +.
 
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