EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: The_torst on September 08, 2020, 02:38:57 pm
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Hello.
This will be my first post and I apologies in advance for my newbie skills and I seek your guidance.
Background:
I own a vintage US car where the common practice is to have combined Turn signal and Brake signal to the rear lights and trailer connector.
My problem is that I live in Europe where these signals needs to be separated on the towed vehicle (trailer).
There are aftermarket modules for this purpose, but I wanted to make this into a DYI project as a learning experience.
I have attached a picture that shows what I would like to achieve and added the module in the middle.
Without knowing how the module is designed I have started to map out a scenario using old school relays to separate the signals, if this is good or bad I dont know but its where I started. I have come thus far that I can get the Turn and Brake signals out, but how I cant solve how the Hazard lights can be identified towards the turn signal output. In my scenario the brake lights would flash when Hazards are active.
And if I can figure out the logic eventually then the next step would to look into how to apply this with using MOSFETs instead of relays for a more durable and smaller packaging.
So if anyone would have any good idea of a different design that could help me on the way I would appreciate the guidance
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cant you tap into the 3 separate lines before the relays in the car,that will give you separate left and right turn and brake signals to control relays for the trailer
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I would suggest actually just trying to install a new wiring harness that has the right signals. Plenty of cars of that style didn't even have a factory wiring harness for a trailer. Whoever installed the trailer hitch would also install the wiring harness, tapping into existing taillight wiring.
You will need some sort of timer circuit to do this without getting access to the separate wires inside the car. Technically you could probably do this with relays and RC timers, but you are going to have a much better time doing it with digital logic.
I would guess what you need to do is that at the falling edge of the "brake" signal, you set a timer. If the brake goes high before the timer runs out, you instead light the turn signals. Thus, when you turn on the hazards, the first flash will be the brake lights but the second will be the turn signals. You will also want a timer where if the brake signal is on for more than X milliseconds, you switch back from hazards to brake lights. That will make sure that if you e.g., tap the break and then press and hold the break you won't be displaying hazard lights. An improvement would be to add a counter to the hazard detection: only after three timed flashes do you switch over to the hazard lights to reduce the possibility of false triggering.
You could do this with discrete logic but I would recommend a small microcontroller. It might seem silly to use a micro for such a simple purpose but it may well be cheaper than a pair of 555s, a handful of NAND/NOT/OR gates and a small counter. Of course the silicon cost is probably going to be negligible anyway for this application: your power switches, connectors, and weatherproof enclosure are going to be more expensive.
You can use logic level MOSFETs or DC capable SSRs to drive the outputs and opto-isolators on the inputs to protect the logic.
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Thank you for your replies.
Yes, one option would be to re-wire the car. However I would like to keep the wiring intact as much as possible on the car, also the diagrams are not super easy to follow. And we have a few more of these cars in my family, so if a "module" could be designed, potentially we could replicate the solution for those cars as well.
And I do realize this is not the easiest or cheapest option to make a diy module.
But I would like to try at least and maybe I can learn something in the process. :)
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For the car/trailer combo you're describing, I expect you'll use an 13-pin ISO11446 plug between them, which means the decoder will be placed in the car.
Am I right here? (Or is the trailer also some kind of vintage?)
The logic is not difficult, the problem is finding a solution robust enough for an older automotive environment (which can be very rough). Choosing relays is not a bad idea.
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The trailer is not a vintage trailer in this case. And I will actually be using the 7-pin ISO 1724 that is the other common standard in Europe.
And yes, the module is intended to be installed on the car.
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The trailer is not a vintage trailer in this case. And I will actually be using the 7-pin ISO 1724 that is the other common standard in Europe.
The trailer must still be pretty old, ISO1724 hasn't really been used for the last 20 years. Main reason: it's missing the backup light. But I've no idea if there are special Swedish rules on this.
Interesting DIY project :)
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North American vehicles have brake-light priority over hazard flashers, so hitting the brakes while the flashers are on, will override them.
The truck already has separate turn signals (with no brake light logic) for the front lamps/dashboard lamps. I would look at using those for the trailer's turn signals.
What do the truck's front turn signal lamps do when the Hazard flasher is on, and you press the brakes? I think they would stay on, so some extra logic on wire #810A would be needed. The Emergency Warning Switch logic is unknown.
You first need to combine (OR gate) the truck's L and R stop lamps to make a single trailer stop-lamp signal, so that it will not flash when turning and braking. I've done this using diodes, but relays like you have or mosfets would work. This is likely all (4 diodes) that's in the 118158 taillight converter. But Hazard lights still interfere and make the brake lights flash.
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The trailer must still be pretty old, ISO1724 hasn't really been used for the last 20 years. Main reason: it's missing the backup light. But I've no idea if there are special Swedish rules on this.
Interesting DIY project :)
Not quite, the trailer is about 12yrs old, and I know there are still new trailers sold with the 7 PIN connector. Although the 13-PIN is becoming more and more common. :)
Swedish Trailer do not require to have backup light as of right now.
Nevertheless I would still need to have separate Turn and Brake regardless of connector choice.
North American vehicles have brake-light priority over hazard flashers, so hitting the brakes while the flashers are on, will override them.
The truck already has separate turn signals (with no brake light logic) for the front lamps/dashboard lamps. I would look at using those for the trailer's turn signals.
What do the truck's front turn signal lamps do when the Hazard flasher is on, and you press the brakes? I think they would stay on, so some extra logic on wire #810A would be needed. The Emergency Warning Switch logic is unknown.
You first need to combine (OR gate) the truck's L and R stop lamps to make a single trailer stop-lamp signal, so that it will not flash when turning and braking. I've done this using diodes, but relays like you have or mosfets would work. This is likely all (4 diodes) that's in the 118158 taillight converter. But Hazard lights still interfere and make the brake lights flash.
Thank you for your input.
I have read on other forums where people have been experiencing the same problem, and their solution have been to run new signal wires from the front Turn lamps to the rear and switch a relay with feed to Trailer connector. This would of course be an option, but one I would like to avoid if possible, both for the sake of not needing to run new wires along the frame of the truck. But also if this 118158 module work there has gotta be a way to replicate the functionality. ???
Anyway, I might setup a bench test and simulate the cars outputs and see what I can figure out using relays and diodes. :D
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What's wrong with tapping the wires going to the front turn lights and the one from the brake switch?
It'll be a longer piece of wire, but it's much easier than decoding the combination brake/turn signal you get at the rear lights. Which isn't really possible anyway.
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[...] You first need to combine (OR gate) the truck's L and R stop lamps to make a single trailer stop-lamp signal [...]
I'm probably being a dim bulb now... :D but I don't understand why it wouldn't be an AND gate? - i.e. you only want the brake light to come on when both L and R are lit... not either one?
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When braking and turning, one lamp is on, the other flashing. You want (both) trailer brake lights on though, so it's an OR-gate for them between L and R, with a NOT.
These schematics I found are the opposite of what OP is looking for, but show some clever logic, where it keeps the lamps off unless both are up.
from https://www.electroschematics.com/trailer-stop-turn-signal-converter (https://www.electroschematics.com/trailer-stop-turn-signal-converter)