My lower taillights is made somewhat strange, where the brake light always is on, but becomes stronger when you press the brake pedal.
I want to change this so that the brake light is off, and turns on when you press the pedal.
How do I detect the change in effect with an arduino, either from the lower taillight wheres theres an change in effect, or by using the top taillight (which works as I want it to, only on when pressing pedal)
I have heard that a voltage divider should work fine, but the output is 21w ~13v and I dont really know if the resistors I have are good enough for that effect. Plus, I am also abit worried about basicly making a «obvoious» short in the car electronics.
A voltage divider should work fine. You can tell if the resistors are good enough by using Kirchoff's law. Aiming for 2 to 20mA of current would be appropriate.
A multimeter would be better, but if the lamps are PWM dimmed a multimeter won't read PWM reliably. And I always say, "A cheap multimeter is better than no meter."
Voltage dividers are NOT for "power". They are for "signal" voltages. For example, it's common to use a voltage divider to measure 12V in a car, dividing it down to 5V or less so it's safe for the Arduino. In this application the resistors are usually around 10K so only a few milliamps flows-through the resistors, and essentially zero current flows into the Arduino's very-high impedance analog input. I assume that's what you're trying to do...
I assume this is a "modern" car and maybe the lights are LEDs? There is probably a controller somewhere. It could be built-into the light assembly or it could be "hidden" somewhere.
Yes they are allways ~12v, but when I press the brake pedal, the current increases, so that the brake bulb shines brighter. Thus I need to check the current when pedal is not pressed and when it is pressed and use the Arduino as a relay/mosfet switch
This is a 2001model car with normal 12v bulbs, I have modded it with leds, but I want to keep the brake lights to avoid problems in case of accident etc.
The problem is that when the brake lights are allways «dimmed» they kinda ruin my fancy led setup
I assume that the best way is to use a voltage divider with the top brakelight and put an arduino and mosfet between the 12v to the bulb maybe?
In other words, you press pedal, top brake light gets power, arduino reads high, arduino opens mosfet, and «full» effect goes into the brake light bulbs.
Ohh ok, but can you make a filter that filters out anything less than a specific duty cycle? In other words, that anything less that 50% duty cycle cant open the circuit
What I mean is, can I make it, is it worth it, or should I just use the third brakelight as control for mosfet? It just means more cabling for my part
Sure, but then how would you power the lamps? You could decrease a duty cycle by cutting power during some part of the cycle, but you asked to increase the illumination. The power isn't there to do that when the duty cycle is low. You could only store the power in a capacitor, but the car computer might detect that as a fault.
I wonder if you are talking about the dual use of the rear light - running light and brake light. They are usually two different bulbs or two filaments in one bulb. That system does not use PWM.
I think you misunderstood me, I am not trying to increase or decrease the illumination/effect of the brake lights. I will draw what I mean with the 3. brake light. Give me 2 sec
I have disconnected wire 3 and using that to power the leds I have put in the taillight. If it was made so that wire 4 only is brakelight, it would not still be on.
But I thought it was like that when I started customizing the taillights.
Theese are the two possible methodes I think is accomplishable. I have no knowlegde about a pwm-filter.
What I think is that when you get a duty cycle e.g over 50% there will be no filtration, but also no need for filtration anymore, until the duty cycle drops below 50% again.