Single wire allows 12v but not 9v

[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?

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

Thanks for any help with this.

 

[(*steve*)]

So, you want to turn on a light when the voltage is above 9V, but less than 12?

Is this to make sure your headlights don't flatten your battery? If so, 9V is way too low, I'd not want to discharge the battery below 10.5V

At 10.5V it may not start the car any more, but at least it's not permanently damaged (yet).

Explain exactly what you're trying to do and we can suggest something suitable.

Me giving you a circuit that turns on a bulb somewhere between 9 and 12V is probably not going to cut the mustard.

 

[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 (non serviceable) 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.

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 current car's circuit board, 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 or something else to control the high beams.

The bottom line is: I need to stop the DRLs; automatically have the low beams come on to replace the DRLs and keep a wire from the car's circuit board when I need to use high beams.
If there is a way to do all this from a circuit board would be great, but using relays and anything else is OK.

Once built, the board/relays input would plug into the Lamp Assembly - Left Front (shown in diagram) and the output for high beam to headlight

In the diagram I do not want to cut any of the cars main wiring, and want to plug everything into the Lamp Assembly - Left Front.

The other problem is I do not want any voltage going back to the car's circuit board, so need a circuit showing everything after the cars lamp assembly front left.
As I mentioned, electrically I understand relays etc, but don't know anything about electronics.

Thanks for the reply

 

[(*steve*)]

OK, so:

1) with zero volts you don't want power applied to anything.
2) with 9V applies you want one circuit activated
3) with 12V applied you want only the second circuit activated.

Sound right?

Here's a circuit shown in a simulator so you can kinda figure out what's going on:

You can duplicate the circuit by importing this into the tool:

$ 1 5.0E-6 2.9224283781234943 54 5.0 43
t 464 288 512 288 0 1 -11.353527746415477 0.5571729210045493 100.0
z 352 288 352 208 1 0.805904783 5.6
r 368 288 448 288 0 220.0
178 512 176 576 176 0 1 0.2 4.728895934235387E-4 0.05 1000000.0 0.02 20.0
178 624 192 688 192 0 1 0.2 4.728895934235518E-4 0.05 1000000.0 0.02 20.0
r 368 416 448 416 0 220.0
z 304 416 304 336 1 0.805904783 10.0
t 576 416 624 416 0 1 -11.353527746415484 0.5571729210045493 100.0
g 624 464 624 496 0
w 624 240 624 400 0
w 624 432 624 464 0
w 512 224 512 272 0
w 512 304 512 464 0
w 512 464 624 464 0
w 448 416 576 416 0
w 368 416 304 416 0
w 304 336 304 208 0
w 512 208 448 208 0
w 512 176 448 176 0
w 352 208 304 208 0
w 304 208 272 208 0
w 448 208 448 176 0
w 448 176 448 128 0
w 576 192 624 192 0
w 624 224 608 224 0
w 608 224 608 128 0
w 448 128 448 112 0
w 448 288 464 288 0
w 352 288 368 288 0
R 128 80 112 80 0 0 40.0 12.0 0.0 0.0 0.5
w 128 80 448 80 0
w 448 80 448 112 0
R 128 208 112 208 0 3 40.0 6.0 6.0 0.0 0.5
w 128 208 272 208 0
181 736 256 736 336 0 300.02534504681023 30.0 12.0 0.001 0.001
181 816 336 816 432 0 302.3228425367773 30.0 12.0 0.001 0.001
w 736 336 736 464 0
w 816 432 816 464 0
w 816 464 736 464 0
g 736 464 736 496 0
w 736 256 736 208 0
w 736 208 688 208 0
w 816 336 816 176 0
w 816 176 688 176 0
w 608 128 608 80 0
w 608 80 448 80 0
o 19 64 0 34 20.0 0.025 0 -1
o 42 64 0 34 20.0 25.6 1 -1
o 40 64 0 34 20.0 25.6 2 -1

The tool is located here: http://www.falstad.com/circuit/

The top zener is 5.6V, the bottom one is 10V. This makes the switching points about 6.2V and 10.6V. I'm showing the input as a varying voltage, but your input would be one of 3 voltages (0, 9, 12). The way I've done it shows you what happens.

 

[paulmackie]

Thanks for the reply.
I have Java, but cannot see the tool or how to input the code to the ap.
Do I have to instal the ap or is it linked on the page?
1) with zero volts you don't want power applied to anything. - CORRECT

2) with 9V applies you want one circuit activated - I NEED THE LOW BEAM HEADLIGHTS TO COME ON.

3) with 12V applied you want only the second circuit activated. I NEED THE HIGH BEAMS TO COME ON
THIS WOULD BE FOR DAYTIME RUNNING. AT NIGHT I WILL HAVE LOW BEAMS ON AND WILL WANT TO SWITCH TO HIGH BEAMS SOMETIMES.

So, with this circuit the high beam wire 9v (currently DRLs) will operate a relay that brings on the low beams, not the high beams at a reduced voltage.
When the low beams are switched on at night, I will be able to switch on high beams when needed. Will this circuit do that?

Is this circuit separate from the low beam wire from the car's circuit board?

Where do I connect the high beam wire input and output in the drawing?

Thanks so much for helping with this.
Paul

 

[(*steve*)]

Thanks for the reply.
I have Java, but cannot see the tool or how to input the code to the ap.

Just go to that page and it will pop up.

So, with this circuit the high beam wire 9v (currently DRLs) will operate a relay that brings on the low beams, not the high beams at a reduced voltage.

Correct. They are always operated from 12V

When the low beams are switched on at night, I will be able to switch on high beams when needed. Will this circuit do that?

This just provides *a* way to switch them on. there is no reason you can't apply power to the lamps some other way.

Is this circuit separate from the low beam wire from the car's circuit board?

Probably.

Where do I connect the high beam wire input and output in the drawing?

To the point where it's labelled "40Hz". You'll have to pick suitable transistors, this will depend a lot on the relays. The resistor values may also need tweaking.

Thanks so much for helping with this.
Paul[/QUOTE]

 

[paulmackie]

Thanks for the help.

Can you write up a parts list, including the size and type of board I need to attach the parts to. I will be using direct wire and not an etched circuit board.

The pop up tool does not appear?

If I connect the high beam headlight input wire to the 40Hz this will allow high beam at night with the low beams on?

Where is the output wire connected?

I will be using regular automotive SPDT relays and I have no idea what resisters to use?

thanks for all your time.

Paul

 

[paulmackie]

I saw this on another forum:
There may be a problem with the 9v DRL feed not being a DC voltage, but a 75% duty cycle PWM of the 12 Volt car power supply.
You may need an RC integrator on the 9/12 volt line.

Not sure how this affects the circuit?

Thanks guys.
Paul

 

[(*steve*)]

PWM will be an issue. You'll need to determine the frequency to be sure of a good solution, but in general a resistor and a capacitor can be used to smooth it out.

Make sure you have the latest version of java installed or it might complain and not load the applet (mine started doing that today after I accessed it -- I've not updated Java yet)

edit: I had to go to my security settings to set the security to medium so that Java would ask me rather than block the application unconditionally.

 

[paulmackie]

Thanks for your help.
So what will the new circuit look like?

Paul

 

[(*steve*)]

There will be a resistor in series with the input followed by a capacitor to ground.

The values of these depend on the frequency of the PWM.