How do I allow 12v but restrict 9v in a single wire?

[paulmackie]

I am building a circuit, but need to know how I can restrict 9v but allow 12v?

I understand electrics, but have no electronics experience.

I have been told a comparator LM339 would work, but am unsure what to do with that?

I simply have a single wire that passes either 9v or 12v from a circuit board, the 9v switches on a dimmed lightbulb (at reduced voltage) and the 12v uses the same lightbulb but brighter.

I would like to stop the 9v light (I am tapping off the single wire and using the 9v to operate a relay), but allow the 12v light.

Could anyone show me the comparator circuit to allow that to happen or some other way to stop the 9v.?

In my drawing can I incorporate the relay into the circuit board and will 9v operate a 12v relay?

I would also need a parts list, so I can buy the parts and make the circuit.

Thanks for any help with this.

 

[MikeMl]

You are not powering the lamp with the 0V-9V-12V signal line, right? You just want to pull-in one relay with 9V and a different relay with 12V?

How may Amps does it take to light the lamp(s) at full brightness?

 

[paulmackie]

I will be powering the high beam light with 12v and redirecting the 9v to operate a relay to bring on the low beam headlights.

The main beam circuit board puts out 9v when the car is put into drive (which are reduced voltage DRLs), when you flash someone or switch to low beam the circuit board outputs 12 volts and stops the 9v.

I switched the OEM headlight bulbs to BI xenon HID single projector lights.

Now the 9v activates the projector solenoid putting the main beam headlights on when the car is put in drive (DRLs - I basically blind people, even during the daylight). So, I want to stop the 9v going to the projector solenoid high beam but by tapping off the circuit have that 9v activate a relay that brings in the low beams, which will replace the DRLs.

I have been told the comparator will allow 12 v to pass and switch on the high beams when needed.

Thanks for your reply

 

[MikeMl]

Let me play it back to you:

1. You have a pin from an existing circuit board.

2. when the pin is at 0V, nothing is on

3. when the pin is between 8V and 10.5V (to build in a guard-band), the driving lights are on.

4. when the pin is greater than 10.5V, the driving lights go off and the high intensity lights are on.

5. the actual current to operate either the driving lights or the high intensity lights does not have to come from the pin (you would be willing to feed a fused 12V instead)?

Do I have it right?

 

[paulmackie]

The DRL 9v does not have to come on for the high beam headlights, but does have to come on to control the relay to bring in the low beams instead of the DRLs; but the high beam which is switched from inside the car does have to come on in case I need to use high beam. If the power does not come from the pin, then I am unsure how the high beams would be turned on.

The circuit I have shown should work, but I need the comparator circuit to control the high beams.

Thanks for your help with this.

 

[MikeMl]

OK, here is a shot at it. I'm back to thinking that the control board can power either set of lights directly, with no direct 12V feed. I am using a simple circuit consisting of a 10V Zener, a NPN Power transistor, and a standard automotive 12V relay.

In the simulation, I am varying the pin voltage (comes from your control board) from 8 to 12V (see the X-axis of the plot). Note that the relay pulls in when the voltage reaches about 10.6V. By using the normally closed and normally open set of contacts, when the trip voltage is reached, the running lights are turned off, and the HID lights are turned on.

The transistor dissipates about 0.3W as the relay pulls in. You could likely use almost any NPN transistor rated for Ic>0.5A and Vce>25V. The diode is used as a transient snubber.
The 10V Zener is the most critical component.

 

[paulmackie]

Thanks for all you effort with this.

I have not worked with electronics before, so please bare with me.

In your sketch you are;
only using the high beam wire.
when the voltage in the cars circuit board pin wire (high beam) reaches 12v the relay operates and turns on the low beam HIDs (The DRLs are 9v as far as I know, and only work when the car is in drive).
The "running wire" will be my high beam (or solenoid on my bi xenon headlight)
the "hid wire" will be my low beams.

So, at night I will be running low beams (which turns off the 9v to the high beam wire shutting off the DRLs, but leaving the circuit intact for high beams when needed), and I may want to use high beams, is that possible with this circuit?

I'm thinking if the low beams are on and I flip to high beams (12v to solenoid HID projector) that will close the relay and switch from the running to the hid circuit?

Is the low beam circuit just left as is and has nothing to do with this circuit?

thanks again for your help with this.
Paul

 

[ChrisP58]

You may need an RC integrator on the 9/12 volt line in front of the voltage detector, as the 9 Volt is probably not a DC voltage, but a 75% duty cycle PWM of the 12 Volt car power supply.

 

[paulmackie]

Thanks.
Can you add the RC integrator to the drawing.

So, the circuit will:
not allow 9v to reach the projector high beam solenoid, but will turn on the low beam headlights instead of the DRLs
with the low beams turned on, the high beams will remain operable.

Where do I connect the input and output wire?

My Parts list would be:
r1 68 RESISTOR
DIODE D1 BZX84C10L
DIODE D2 1N4002
12V SPDT RELAY
R2 10 RESISTOR
R3 8 RESISTOR
Q1 2N3055
V1 IS THIS ALREADY ON THE CAR'S CIRCUIT BOARD, OR IS IT PART OF THIS CIRCUIT?

What size and type of board do I attach this to? i will use wires and not an etched board.

Thanks again for taking the time to do this for me.

Would I be able to order these parts online?

Paul

 

[MikeMl]

Chris is right. The 9V you measure is probably the result of the 12V being pulse-width modulated. Your meter would integrate the PWM waveform and trick you into thinking that the voltage is only 9V where in reality it is 12V for 3/4 of the time, and 0V for 1/4 of the time. In that case, neither a comparator or the circuit I posted will work.

One approach is to use a 555 timer chip as a retriggerable multivibrator. The relay would be switched when the pulses disappear. Another approach is to integrate the pulses to create a "filtered" dc output before feeding that to the 10.5V detector.

 

[MikeMl]

...
r1 68 RESISTOR
DIODE D1 BZX84C10L
DIODE D2 1N4002
12V SPDT RELAY
R2 10 RESISTOR
R3 8 RESISTOR
Q1 2N3055
V1 IS THIS ALREADY ON THE CAR'S CIRCUIT BOARD, OR IS IT PART OF THIS CIRCUIT?

R2 represents the resistance of the Running lights. It is there for simulation only to show what the relay does.
R3 represents the resistance of the HID lights. Your existing lights wire to the Normally closed and normally open terminals of the relay.

V1 is the (DC) voltage that comes out of your existing pcb. However, now there is doubt that this really is a DC voltage, so a filter would have to go between the pcb and the input of the voltage detector. I will have to think about how to do the filter...[/quote]

 

[paulmackie]

That would be great.

Thanks for taking the time to do this.

Paul

 

[MikeMl]

Paul, I need more information. Here is what I would like you to do:

Wire the output pin from the existing pcb to incandescent lamp(s) (the original running lights?, do not use the High Intensity lamps).

1. Measure what you called "9V" with a DMM in DC volts mode two ways;
1a. engine stopped =
1b. engine running >1500rpm =

2. Put the meter in AC Volts mode and repeat the measurements;
2a. engine stopped =
2b. engine running >1500rpm =

3. Do whatever it takes to make the pcb output what you called "12V", leave the incandescent lamp load in place. Measure DC Volts;
3a. engine stopped =
3b. engine running >1500rpm =

4. Measure AC Volts;
4a. engine stopped =
4b. engine running >1500rpm =

Post all eight measurements (1a,1b,2a,2b,3a,3b,4a, and 4b), and we will go from there.

 

[paulmackie]

Thanks for your reply.

Will try to get them tonight, but I may not be able to do this until Tuesday evening.

The DRLs only come on when the car is put into drive, so you want voltage measurements with DRLs on PWM mode, and High beams on (12v) all with engine stopped and engine running.

Thanks again.
Paul

 

[paulmackie]

I could not put in the old incandescent lamps as the retrofitter changed the fittings, so all voltages are using 6.7v DRL voltage or high beam 12v voltage with HID bulbs. I would have to get adapters to fit the incandescent bulbs.

DRLs
1a lights not on 0 volts
1b - DC 6.7v
2a lights not on 0 volts
2b - 7.6AC volts

High Beams
3a - 11.8DC volts
3b - 12.9
4a - 5.2v then 12.1v and drops to 0v
4b - 1.7v

Can you work with this or will I have to get an adapter?

Thanks.
Paul

 

[MikeMl]

It looks to me that your magic, built-in control pcb is doing Pulse-Width modulation both while in DRL mode and in High Beam mode, so we cant use the presence or abscense of the pulses to decide which mode it is in. That means we will have to use a filtered version (average voltage) to trigger the voltage detector.

I have an idea how to do that, but the circuit I posted last night is on another computer. I'll modify the circuit and post it tomorrow.

It is 11:39pm here,

Out,

 

[paulmackie]

I am on mountain time here in Calgary Canada.

It seemed to me like the voltage started low and then went up and steadied off to a final voltage with the engine running. I had to put the car in neutral with engine running to get the readings; when the emergency brake is on it cuts out the DRLs.

Thanks for taking the time to do this for me.

Paul

 

[paulmackie]

Hi Mike,
I got this reply on another forum:
https://i1048.photobucket.com/albums/s376/jimkeith99/q9Vvs12Vschem2_zps0cc98db1.jpg

Afterthought: Make D2 a 1N4148 signal diode

Not tested

Would this circuit turn off the DRLs, turn on the low beams and allow high beam?
Where would I make the input connections from the DRL/high beam and any other connections.

Thanks.

paul

 

[MikeMl]

Seems overkill, and there is no relay output.

I had already started down the same road, but I think my circuit is better than the one you posted. Mine is ratiometric, meaning it is detecting pure pwm percentage, independent of the actual car voltage which changes as the engine is reved up. The circuit you posted compares the filtered pwm voltage to an absolute voltage reference.

Here is the new circuit. I would build and install it in two parts.

The module containing the comparator is hand-wired on a small Vector board. It has four connections to the outside world. SW12V comes from the car's fuse panel. It should be live only when the key is in the "Run" position (to prevent the circuit from killing your battery). In comes from the existing controller. Rly86 is an output that goes to pin 86 of a standard 12V automotive relay. And last but not least is a local connection to car's chassis.

The second part is the 12V automotive relay. Put the snubber diode D2 right across pins 86 and 85 of the relay. Pin 86 is fed from the module. Pin 85 goes to ground.

You can do anything you want with the relay contacts. I would feed the High Intensity lights as shown, using the same fused, switched 12V power source as discussed above.

The parts can be procured from Digikey, or a comparable local supplier. These are clickable links:
**broken link removed**(Note that you can download a data sheet from here.)
2N4403
**broken link removed**
Relay (This one has the D2 diode built-in, so you don't need to wire one across the coil)

Have fun.

 

[paulmackie]

Hi Mike,
Thanks so much for this.

As I mentioned I am not familiar with electronics, but will give it a try.

Questions:
So, basically the board is turning PWM into 12 volts, which activates a 12v relay to bring on the high beam?

You mention Rly85, is that shown as Rly86 in the diagram, or is that something else?

I see how the diagram brings in the high beams from Rly86 by closing contact 30 & 87, but what brings on the low beams to act as the DRLs? How is the low beam headlights connected to this circuit? I will need the low beams on instead of the DRLs for day time running, and use of the high beam when needed.

The H13 FEMALE connector has three wires one for low beam, one for DRL/High Beam and a ground, do I connect the MALE H13 pigtail wires to the circuit board, and use those as the ground, DRL (now low beam feed) and low beams. I'm thinking the car's low beam light switch is obsolete as the low beams will come on automatically when the car is started? Normally I start the car, the DRLs put on high beam headlights when car is put in drive, so I switch on the low beam headlights, which turns off the DRLS and use headlights for day time running. There is no problem at night as I turn on my low beam headlights and am able to use high beam when required.

The vector board: is there a certain type or size? I'm thinking a board you put the pins through and solder the other side to hold the part in and then attach a wire to the other parts, then cut the board to fit a plastic box?

Once the board is done I'm thinking to put the board in a sealed plastic box and run the H13 and HID connectors from the box, have you any recommendations as to what box I should use?

Do I have to be concerned about heat in the plastic box? Do I need heat sinks

What is the gauge of the wiring to SW12v?

What is the gauge of the wiring used to connect the parts on the circuit board?

Do I just mount the relay to the board and solder the wires to the pins, or put the pins through the board and solder wires from underneath the board?

Should there be a fuse on the board?

Is there any way that this circuit can affect the cars computer system? If it shorted out, voltage feedback etc.

External Connections are:
In - feed from DRLS and high beam
two SW12v - both fed from same 12V feed from any ignition run position source (what gauge wire?)

My parts list is:
Vector Board
One - R1-10K Resister
One -R2-1K Resister
R3-?
One -R4-33K Resister
R5-?
One -R6-33K Resister
One -R7-1K Resister
One -R8-470K Resister
One -LM 393 Comparator
One -2N4403 Transistor
Two - 1N44002 Diodes
One -Relay 12v SPDT
one - 10u Electrolytic Capacitor
one - 1.0u Electrolytic Capacitor
Is that everything?

Sorry for all the questions.

Paul