Hi All,

I'm attempting to restore a Camaro from the 80's that uses pcb's to control the lighting for the car. The retro "light module pcb" is discontinued, and finding used ones that work is difficult. The most common problem is that over time the electronic components wear out and when the headlights are activated the lights flash on and off repeatedly... pretty annoying when trying to drive at night.

The module functions as follows:

When the driver presses the headlight "on" button a ground signal is sent to the solid state (light control module) that then energizes the relays for the headlights.

Most automotive headlight switches are mechanical and simply complete the ground for the headlight circuit. My switch is not mechanical and relies on the programmed instructions on the pcb to then activate my headlights.

I could bypass my module to get the headlights to activate but it would require me to use a mechanical switch. I would like to keep my stock switches that simply send a ground signal when pressed.

So here is my question:

Is there a way to build a simple circuit that when sensing a ground input, energizes a relay and keeps the relay energized until another input directs it to de-energize?

If it is possible to do this, what would be the easiest way to create this?

Best,
Alex

 

The most common problem is that over time the electronic components wear out and when the headlights are activated the lights flash on and off repeatedly... pretty annoying when trying to drive at night.

I had that happen on a 1965 vehicle. The headlamp shorted. There was a thermal breaker on the headlight switch. Annoying --- yes,

You kinda mentioned how to turn the headligths on, but how do you turn them off?

i can think of something really wacky, like a conductive elastomer. It's used in calculator keyboards.

This is a one on one type of thing, right? Not like a GM steering controls which is a bunch of resistors? Each button creates a different
resistance.

So it looks like you want a momentary press to turn the lights on, but what about off? Do you have any idea how much current can pass throught he switch? Any schematics whatsoever?

 

Thanks for the quick reply,

I've attached a diagram from the car manual.

There are three buttons on a control pod: Headlights, Off, and Highbeams. It seems each is simply a ground that triggers the solid state to complete a programmed set of instructions.

When held down the buttons ground the wire associated with them, but as soon as it is depressed the ground circuit is incomplete.

What I'm trying to accomplish is a more rudimentary setup with relays, but with a momentary press to turn them on the lights, activate high beams, and turn them off.

 

the schematic is A LITTLE confusing. You have HEADLIGHT, ON and DIM which are strange labels.

Do they come on in high beam (HEADLIGHT) and go into LOW beam when you hit low or something else?

Can you measure the resistance of a closed switch in the POD?

Do any of the switches work?

You do have some latching type of arrangement that seems to happen. is there anything else that happens like headlights stay on for short amount of time after the car is turned off.

I would be worried about how much current those switches can take.

The labels are confusing an I don't know how it;s supposed to operate. At least one of my cars had individual headlamp fuses and it was nice.
Worried just how much current those POD switches can handle. Define what happens when you push each button.

I had momentary bright and bright always as well as on/off.

On the vehicle in question, I wired a buzzer between the driver's door switch and the parking lamp and got a buzzer when the driver's door and lights were on. A few diodes were used too. It was a great headlights on reminder.

Speculation of the failure mode: Lamp filament shorts. C.B. causes blink because of self-reseting. It may not be a module failure after all. Just pull the headlamp connectors one at a time and see if one lamp stays on. Been there. Done that.

Long term recomendation is to individually fuse the high and low beams of each lamp separately.

 

Keep It Simple,

I'm not sure why it's labeled dim because that is the wire that goes to the brights button.

When the headlight "on" button is pressed the low beams are on by default. The high beams come on when the brights button is pressed, and de-energize if is pressed again. I've attached a diagram that shows how the buttons are arranged.

I'll measure the resistance tonight, but I would like to only use the switches as momentary triggers. They are not really switches but some type of momentary ground trigger that signals the solid state to perform an action.

All of these switches work, but after a few moments the headlights start blinking and eventually shut off. I can hear the relays/circuit breaker in the solid state going crazy when this happens.

I was thinking about something like this to energize my new relay setup for my headlights, but I don't know to wire the reset since my headlight "off" button sends a ground signal as well.


Best,
Alex

 

Why can't a latching relay be used? This is just the first one I found, so they are available. One for low beams, one fro high beams. https://www.autoelectricsupplies.co.uk/product/178/category/36

 

To satisfy my curiosity:

Let's assume low beams only.

1. Pull one headlight connector. And do the on/off thing.
2. Put it back on. Pull the other headlight connector. Do the on/off thing.

You can set up DPDT relays in a self-latching configuration, but those automotive relays take LOT of coil current and that may be too much for your FOB.

I'd like to aim for about 3-10 mA through the FOB.

So,my thoughts are to use a photomos or optomos relay which is an IC chip or LED and FET with a dual coil latching relay. The LED current can be set for 3 mA with a resistor or current source. The current source e.g. http://www.ti.com/product/LM334 is probably a little better. A few diode for coil protection. One coil for on and another for off. The 3 mA is a decent wetting current.

The push-push is harder, but a part from ELM electronics should help.

 

@ Keep it Simple

I am just learning the basics of circuitry, but I would love to be able to fix this. I have basic wiring/soldering skills, but I'm lacking on the terminology still.

Could you draw a diagram of how to set this up, and what parts I would need?

I realize this is a lot to ask, but I would really appreciate it!

Best,
Alex

 

Right now and especially today, I don;t have time to scribble something. This https://www.digikey.com/product-det...ic-works/TQ2SA-L2-12V-X/255-3464-1-ND/2810292 is a dual coil latching relay and at 12 V it only takes bout 11 mA. This is probably safe.

The contacts are rated at 2A, so they can easily switch the bigger relays.

Usually the coils are labeled set and reset and have polarity markings. A pulse in the direction of the polarity marking, moves the coil to say set or reset. If you reverse the polarity set would become reset and vice versa. What happens in these relays is that a small permanent magnet can hold the relay in any states but it's not strong enough to switch states.

To protect solid state devices or in general transistors switching the coils a diode, like a 1N400x (4001, 4002) series is placed across the coil so it normally won't conduct.

This easily does, the low beams, but not toggling of high. Nor would off turn off the high beams unless you design it this way.

They aren't big and you;ll have to learn how to breadboard with them.

See what voltage F, C and N are at when no button is pushed. They might be at 5V.

This https://www.elmelectronics.com/ic/elm411/?v=7516fd43adaa could actually be a good basis of a design.

You might be better off using a 5V latching relay such as this one https://www.digikey.com/products/en?keywords=PB1618-ND and a 5V non-latching for the high beams.

The ELM IC would drive the latching coils and would toggle the coils on the on/off portion and the dim side would always toggle off when the car powers down.

So, even though these use contact closures to ground, they have 5V on the push buttons when they are in the off state and I suspect your gizmo might too.

it can get a lot more involved than you would like, but it seems easy and doable to me.

Right now, I can't explain anything.

 

Having thought about it overnight, and the fact that the ELM consumes power and standard headlight switches work all the time:

1. Use this https://www.eeweb.com/extreme-circuits/momentary-switch-teamed-with-latching-relay sort of circuit for DIM

2. The ON/OFF is easy. That's just ON for one coil and OFF for the other.

You want the coil currents to be low and 12 mA is considered low. The contact ratings need to handle the automotive relays which, I think, are around 500 mA. 10 mA is a good current to keep the contacts clean.

The ELM part can probably still be a possibility at 1 mA at 5V, but the car would always be drawing power. All cars do now a days.
This http://www.ti.com/lit/ds/symlink/tle4275-q1.pdf might be a decent 5 V regulator to use.

The ELM part uses internal 5 V pull up resistors. That just means that there is a resistor to +5 V internally or one from the side of the switch going into the IC.

So, two ideas. Not sure if this gives you enough to go on.

 

I'm having a difficult time mapping this out,


Is the 12v in this circuit what would need to go to my relay for the brights, or is it the constant 12v from battery? I also don't understand what the three wires in the green circle mean unless it grounds what will be the relay for my brights.


So for my low beams/off I would need a regulator that would go to the ELM 411 which would be connected to a latching relay?

Which one of the inputs would need the on and off switches need to be connected to and how does it wire up to the relay you suggested?

I may be in over my head here...

 

Is the 12v in this circuit what would need to go to my relay for the brights, or is it the constant 12v from battery?

The 12 V shown in the diagram would be battery.

I also don't understand what the three wires in the green circle mean unless it grounds what will be the relay for my brights.

Note the symbol is CON1 or Connector 1. One of the contacts in the relay is used to support the circuit The other set of SPDT contacts you can use as you want.

i.e One contact to GROUND and the other to BEAM CHANGE RELAY CONTROL

(I'll address the other stuff later)

There are two totally different designs here: One design is based on a 12 V DPDT and a 12 V SPDT latching relay and the other is based on a 5 V SPDT latching relay, the ELM chip and a 5 V regulator.

EDIT: Fixed the quoting

 

Maybe I am off course but why not just repair the module itself? Often times it is just a matter of reflowing the board or replacing components which are still available. I do a lot of automotive boards and most of them are fairly simple to repair. Just a thought. Can you post a picture of both sides of the board?

 

So for my low beams/off I would need a regulator that would go to the ELM 411 which would be connected to a latching relay?

Plan B: (the second proposed plan) would be to use the ELM in toggle mode as the "latching" part for the low/high beams. If the battery were disconnected, hopefully the state of the high beams would be off. The 1 mA at 5V and the quiescent current of the regulator would draw power all of the time. We should be able to drive the low/high relay with a few extra parts.

The ON/OFF portion would just drive the set and reset coils directly on a 5V latching relay.

In this design it makes more sense to keep nearly everything +5 V.

 

The ELM specs are contradictory. Contacted ELM. Reminder: I tended to look at gross functionality first, then details. I was aware of the ELM part, aware of latching relays and the 5V regulator. Just not the specifics, I possibly was misled when the first page of the datasheet says 25 mA of drive and the table part of the datasheet is <10 mA with asymetric source and sink currents. When I design stuff, I conceptualize and then throw out possibilities no matter how absurd at first. Then decide on the best approach. I initially forgot that lights generally work all of the time or at least used to.

They can turn off after a preset time after the door is opened or turn off when the driver's door is opened. Then, there are the DRL's or daytime running lights. GM has retained accessory power or power that sops, not when the ignition is turned off, but when the driver's door is opened.

 

Maybe I am off course but why not just repair the module itself? Often times it is just a matter of reflowing the board or replacing components which are still available. I do a lot of automotive boards and most of them are fairly simple to repair. Just a thought. Can you post a picture of both sides of the board?

Sorry for the late reply. It is final exam week and things have been hectic. I'll pull the module and take a picture here in a bit!

Best,
Alex

 

The ELM specs are contradictory. Contacted ELM. Reminder: I tended to look at gross functionality first, then details. I was aware of the ELM part, aware of latching relays and the 5V regulator. Just not the specifics, I possibly was misled when the first page of the datasheet says 25 mA of drive and the table part of the datasheet is <10 mA with asymetric source and sink currents. When I design stuff, I conceptualize and then throw out possibilities no matter how absurd at first. Then decide on the best approach. I initially forgot that lights generally work all of the time or at least used to.

They can turn off after a preset time after the door is opened or turn off when the driver's door is opened. Then, there are the DRL's or daytime running lights. GM has retained accessory power or power that sops, not when the ignition is turned off, but when the driver's door is opened.

Does this mean it won't work?

 

Hi

You could do something like this

 

eetech gave you a third idea.

Microchip's response/

The 'up to 25 mA' quote is taken from the Microchip literature, and is a maximum rating that does not take into account the voltage drop across the driver transistor. Page 3 of our data sheet shows you the current you might expect, with reasonable maximum (as we quote) voltage drops across the driver transistors.

It looks like MC is being very conservative. This would be for the ELM version. BTW, the ELM parts are custom PIC micro controllers with a dedicated firmware to perform a specific function.

It does not mean it won't work. The good part is that the current is needed for a short time. It might require more parts.

A dedicated processor with your own code may be able to take advantage of better sleep states. This is beyond the scope of this thread.

As I see it, the relay only approach might need a little tweaking to work. It say that in the article. Drawing nearly no power is a good thing.

The ELM approach uses some power. So, you might have to start the car once a month which isn't unreasonable. The regulator chosen is automotive qualified. This generally means more reliable and an extended temperature range. The automotive environment is hostile, but you design for it.

You might try both approaches. There's a lot of stuff the TS/OP (Thread Starter/Original Poster) doesn't know. The printed circuit board would be the most reliable, but you can can breadboard stuff too.

 

Hi

You could do something like this View attachment 141133 View attachment 141134

Thank you for putting this together!

The on/off are two seperate pushbuttons. That being said, how can I incorporate the two different buttons with your design?

Best,
Alex