Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

12 volt Vehicle Switched Circuit - Not Entirely Sure!

Status
Not open for further replies.

Funky Diver

New Member
Greetings everyone... having hung about randomly for a couple of days now, I still can't find a definitive answer so I'm gonna ask the question that has now got me completely dumbfounded.

Scope - to operate fog light relays on a car using a rotary switch.

Now in itself the concept is fairly simple.

**broken link removed**

The fog light switch is on the top left stalk. This is a two section switch, the normal headlights are on the outside end of the stalk, then another rotary section further in for the foglights.

To switch the lights on, you rotate upwards once for rear light, then again for front. To switch off, is rotate down in the same increments.

Turning the main lights also resets the fog lights to the off mode.

So now I'm completely flumoxed! The rotational switching applies a contact to turn the lights on in turn using hte same contact, and a seperate contact is created to do the reverse.

I've tried thinking through ALL sorts to achieve this, and ordinarily I'm quite good with relays, etc... but it's a long time since I've done anything with logic stuff and I think I'm just getting myself confused.

Power source is 12 volts. Fog lights are already operated by relays. And before the question is asked, this is going into a VW not a Peugeot, and it's to rid myself of switches on my custom dash board.

Help?
 
Last edited:
Chances are, that in the original application, the UP/Down counting logic was part of some micro-controller box. If you are using just the switches without the underlying controller, you will have to build at least a simplified equivalent of the missing box, using some CMOS Logic chips. Is that what you are asking for help on?
 
Hi Mike,

It sure was, all the circuitry for that part of the original application is actually still located within the large black box that the stalks are attached to. I was going to use it for attaching the wiring to the existing pads whilst breaking the traces to the "stuff" that I don't need.

In my application however, I just need the switching elements to replace good old fashioned mechanical connections. All of hte other switches that you see on the stalks are straight forward twist / push to close contact type switches so easily transferred across.

In terms of the final outcome, I am not bothered about the HOW so long as it is practical and works. I had considered using a PIC with a simple programme to do this, however I have neither the expertise or the hardware to achieve this at this point in time. If, however, this would be the best solution then so be it, but wanted to exhaust the the other options too in case there's a simple trick I'm missing.

Cheers,
Rich
 
Last edited:
As the switches return to their original position, you need something to remember whether the light is on. It is likely that the foglight switch has two contacts, one for up and one for down.

You could disconnect the switches from whatever they are connected to at the moment. You would then need to have a latch or microcontroller or something to store the current state.

Alternatively, you could leave the current electronics, and run a relay from the foglight outputs. You might need a resistor to fool the car into thinking that the lights haven't failed.
 
As the switches return to their original position, you need something to remember whether the light is on. It is likely that the foglight switch has two contacts, one for up and one for down.

You could disconnect the switches from whatever they are connected to at the moment. You would then need to have a latch or microcontroller or something to store the current state.

This is likely the route that I need to take.


Alternatively, you could leave the current electronics, and run a relay from the foglight outputs. You might need a resistor to fool the car into thinking that the lights haven't failed.

My car aint that advanced, lol. Bear in mind we're working with 70's automotive electrical technology here, and trying to shoehorn 90's switching arrangements into the mix.

The current system uses mechanical switches, which flip a relay to turn the fogs on.

This works for both front and rear lights.



I suppose the way I envision it working is...

Side lights on - powers the circuit to allow the fogs to come on when the appropriate switching has been achieved.

1. Rotate the fog lamp switch up once - activates the relay for the rear fog lights

2. Rotate the fog lamp switch up again - activates the relay for the front fog lights

3. Rotate the fog lamp switch down - deactivates the front fogs lamps

4. Rotate the fog lamp switch down again - deactivates the rear fog lamps



The key element being that if only the rear fog lamps have been illuminated, then the down rotation of the switch needs to deactivate the relay supplyinf power to the rear lamps. I'd tried designing a circuit with transistors and relays, but in reality it's been that long since I did any of that type of electronics I was just getting myself confused. In terms of the practical soldering it all together, I am not in the slightest phased by it, so long as I have a workable circuit diagram to go off. Thankfully this isn't a "critical" circuit, so failure at any point is not going to be life threatening (say like with the main lights)

Thank you for hte responses so far, at least it's giving me a chance to clarify what I need to do :p
 
Last edited:
It would really help to know what vehicle this switch is from. Then you can look at the wiring diagrams for that vehicle to see exactly how they wired it. You might find something interesting in the diagrams that all of a sudden makes sense.
 
Nah, that won't work.

The switch gear is standard Valeo, found in Peugeot, Vauxhall Commercial, Citroen, etc etc. and is part of a much greater system, of which I am not even contemplating fitting.

There is nothing inside this gear that will help me integrate it to my VW, which as I said is using 1970's technology. In other words, switches making direct contact to form a circuit. It IS the simplest form of circuit in use I would imagine.

If anything, the final solution to this will be the most advanced electronics found on the car, that's for certain (beyond the ICE of course)
 
Think I may have sussed it... a bit :p

Apologies if this is using vehicle schematics, but seeing as it's an vehicle application, probably appropriate.

**broken link removed**

Anyone care to cast a beady eye over it for me to proof the circuit please?

Thanking you all for your help so far :D
 
What you've drawn wil turn on the lights when you press the button, but they'll turn off as soon as you let go.

You are going to need some electronics, or lots of relays.

You need something to remember that you have pressed the button. You can use a relay for that, but it really gets complicated when you get into counting button presses. You need a relay to remember that the button has been pressed, another to remember that it has been released (after being pressed) and a third to remember that it has been pressed a second time.

If you don't mind turning them all off in one go, you could de-energise everything to turn off.
 
This is what you need. It's not my best diagram. I really should get some printed circuit layout software running on this computer!

I have omitted the earth wires to terminal 86 on each relay on the diagram, but they will obviously be needed. You need to remove the power to turn the lights back off. You can use another relay and the "off" switch for that.

Using automotive relays means you need lots of relays as they only have one contact.

Relay 1 just mimics the pushbutton.
Relay 2 stays on when the button has been pushed, with current from its own contact 87
That turns on the rear fog light
Relay 3 mimics relay 2.
When relay 1 is off (the button is released) and relay 3 is on (the button has been pressed before) then relay 4 turns on, and stays on using current from its own contact 87
So relay 4 is on when the button has been pressed and released.
Relay 5 mimics relay 4
When relay 1 is on (the button is pressed) and relay 5 is on (the button has been pressed and released) then relay 6 turns on and stays on with current from its own contact 87.
That turns on the front fog light, and the rear stays on.

(Obviously you can swap the front and rear fog lights if you want).

You could combine relays 2 and 3 to one relay and 4 and 5 to another one if you can find double pole relays.
 

Attachments

  • FogCircuit.jpg
    FogCircuit.jpg
    60.2 KB · Views: 239
hmmm... that's a lot of relays, and truth be told... all a bit confusing, lol.

Had a bit more of a mooch around on the site, and the web in general and came up with a decade counting circuit, but only using the first two outputs... after that it doesn't matter and as they're sequential, the switch can work as a clock input. The beauty of it is that I think have nearly all the components to build a test rig but won't be able to pick up my relays until Sunday (boo hissssss!) *Edit* Just realised I've missed off the voltage... the black line leading in from the right, a third way down at 12volts. */Edit*

**broken link removed**

Not 100% on the use of all the capacitors in the switching circuit though (what ARE they for?)

Cheers,
Rich
 
Last edited:
Realised that I needed to sort out the resistance balance on pin Out 4. Here's the result... now if someone with a greater knowledge than me could proof it, I'd really appreciate it.

**broken link removed**

I'm regurgitating learning that I did over 20 years ago on this, and honestly quite surprised I remember so much (including the Resonance Frequency equation, haha... )
 
Last edited:
The capacitors across the switches are to reduce the chance of switch bounce causing the 4017 to count multiple times. That's not needed on the reset line.

You should connect to outputs 1 and 2, so that one press turns on one light and the second press turns on the second light as well.

It would be a very good idea to feed all the low power stuff (everything except the relays and lights) through a 100 ohm resistor, and to put a 15V zenner after that, to ground. There are evil spikes on car electrics.
 
Cheers, Diver, that's much appreciated, and yeah, the connections are to outputs 1 and 2, just the pin numbers aren't one and two, lol.

So basically whack in a 100 ohm resistor where I have 12 volts and a Zener where my earth symbol is and we're golden?

I have those anyways, so at least we're just waiting for the parts to arrive :D
 
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top