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Help required...filtering DRL voltage level for switching on two circuits on (12V DC)

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bluebastide

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Hi

I am looking for a simple circuit diagram that would trigger on two 12v circuits on my car based on the voltage level of the DRL input to my DRL/High beam bulb.

These are things to take care of:

1- DRL in Canada is mandatory on all cars since the 90's. In automatically either switch on a bulb in one of the headlights or, like in my car, sends either 4.7v to 6volts to the HIGHBEAM Bulb when I turn the ignition on or sends 12V to the same bulb when I turn the HIGHBEAM on. Therefore my HIGHBEAM bulbs act as DRL.

2- I want to filter the input voltage and turn two relays or triacs (or whatever) ON based on this simple algorythm :
A- No voltage = All circuits open - no bulb on
B- Any voltage say over 1V = Circuit 1 closed
C- Voltage above a certain threshold = Circuit 2 closed

3- I would use the circuit 1 closed to feed 12V (from the battery) to a new set of Angel eyes and circuit 2 closed to feed 12V (from the battery or from the input of this circuit) to the HIGHBEAM Bulb.

4- Due to the CAR environment (humidity, ...) a simple, cheap and compact circuit should be looked at.

Thanks for your toughts and ideas
 
1- DRL in Canada is mandatory on all cars since the 90's. In automatically either switch on a bulb in one of the headlights or, like in my car, sends either 4.7v to 6volts to the HIGHBEAM Bulb when I turn the ignition on or sends 12V to the same bulb when I turn the HIGHBEAM on. Therefore my HIGHBEAM bulbs act as DRL.

You are absolutely sure when the DRL are on it used a fixed lower voltage? The reason I ask is because this recently came up in another thread and it seems many systems use PWM rather than a fixed low voltage. Simply measuring with a DMM is not a reliable option to determine what you have.

Ron
 
Hi Ron,

I did not even read electronics for dummies thus I am almost starting from scratch. I do understand what PWM means by looking around. I can't tell either. I do know 3 things: the car is a BMW 328 97 would PWM used in those years ? I used a DMM and the voltage is steading at 4.7 v when ignition is turned on and 6 v when engine started.

After some search I cannot confirm if this car uses pwm.

Is there a simple way to asses that ?

Thx
 
Creating a circuit to do what you are looking to do as far as voltage would not be difficult. For strictly voltage you could use a comparator type circuit. The problem is that if PWM is used, and for a '97 there is a good possibility then the use of a voltage comparator would not work. I know there are BMW forums out there and someone must have a correct answer. Like you, I looked but could not find out how it is done. I also suspect PWM because of the voltages you observed using a DMM. I just don't know. Hopefully someone will come along who knows with an idea.

Ron
 
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If you scroll down this page you will see some examples of the type of comparator circuit(s) I mentioned. We apply one voltage as a reference. We can set up the comparator to output when an input voltage exceeds or is below the reference. Pretty much a small handful of components. In this case for an automotive application the reference voltage(s) could be set using a few zener diodes.

This can get a little complicated for someone with no electronics background.

Ron
 
Ron

Would the 4 level comparator the best choice by removing 2 levels and replacing the led by triacs or relay to turn on - off my two circuits ?

With a circuit diagram, the values and numbers of ic, res, cap, ... I think I could manage to built it.

Thx
 
Ron

Would the 4 level comparator the best choice by removing 2 levels and replacing the led by triacs or relay to turn on - off my two circuits ?

With a circuit diagram, the values and numbers of ic, res, cap, ... I think I could manage to built it.

Thx

No, you don't need the quad. The LM393 would be fine for just two levels. Later today with some time I'll make up a circuit and include the values for you. Something that should work. Remember we are assuming voltage and not PWM. :)

Ron
 
That's great thanks but before you spend some time in this, do you think I could use my DMM frequency measurement to see if there is some sort of pulse (PWM) ?

Thx
 
Now that is a good idea. Let's see if you find a frequency when they are daytime running.

Ron
 
What kind of car is it? When I saw Angel Eyes I thought of BMW. Knowing the vehicle will help immensely as you might already have a relay (or relays) operating the DRL's in which case you could rely on the triggers for those to operate your circuit.

I know of 4 methods to control DRL's from my work in the automotive field:

1. PWM to reduce the output of the high beams (the most common system now used).
2. A large power resistor (far less common now) to reduce output to high beams.
3. Relays to switch the highbeam bulbs to be connected in series, reducing output of each (common on lots of GM vehicles).
4. Simply turning on a different light at full power, be it the low beams, fog lights or in some vehicles a special DRL only bulb that also sits inside the main headlight housing.
 
Here are some hints:

The car is a bmw e36 328i 1997. No idea at this time if drl is using PWM. As far as for DRL implementation in this model based on your 4 approaches, I would tend to say:

1. PWM to reduce the output of the high beams (the most common system now used).
. unknow at this point
2. A large power resistor (far less common now) to reduce output to high beams.
. Could trace back to actual drl relay and see...if that was the case, finding the resistor and the relay would be the easiest way to a solution to the objective.
3. Relays to switch the highbeam bulbs to be connected in series, reducing output of each (common on lots of GM vehicles).
. I doubdt as when I tested one connector not hooked to the bulb, I got those 4.7v and 6v readings
4. Simply turning on a different light at full power, be it the low beams, fog lights or in some vehicles a special DRL only bulb that also sits inside the main headlight housing.
. That I am sure it is not. 2 wires only go to the main bulb in the headlight beam housing.

thx
 
These are the result of DMM Frequency test:

Bulb connector not attached to bulb.

- Ignition off = 0 KHz
- Ignition On, car started, DRL ON = 0.052 KHz +/- 0.003
- Ignition On, car started, HIGHBeam ON = 0.500 KHz +/- 0.03

I cannot interpret those values. But I can interpret my son's face when I told him we would strip its DRM relay connectors out!
 
^ Your second reading with high beam on makes no sense. I think it's just noise from the engine on. The first reading is correct - the PWM frequency is 50Hz. for your car.

My understanding is you have a DRL relay under your dash on the driver side. It'll probably be blue and will be taller than a normal relay. If you replace the DRL relay with an ordinary high beam relay (has to be from BMW as it's not a normal 5-pin relay) then you lose the DRL function and your high beams only come on when turned on (like with a US car). BMW made it this way so a simple relay change could enable or disable DRL's for different markets.

Then you only need to make a circuit to power your new DRL angel eyes when the ignition is on. Much easier than making a comparator to turn on a relay with a lower PWM voltage, IMO.
 
adamey, glad you came along.

Ron
 
I am glad both of you came along to help me narrow this down. Stay subscrived, I will find some time to track this relay and see if I can do something around it.

thx
 
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