Need help wiring up something by tomorrow (story inside)!

[Insipid]

Hello!

I have a situation, I have to have my car compliant by Tuesday and I only have tonight and tomorrow to work on this project. So if I could get some quick help in the most basic way that would be fantastic!

I have a situation similar to this thread: https://www.electro-tech-online.com/threads/relay-required.160143/page-2

I have an electronic parking brake (EPB) line that I need to tap into, here's the schematic:

https://imgur.com/DsDT3G6

Basically the W/G line on the EPB switch (rather than going to ground) goes to 0.2v when the parking brake is on and then goes back to 12v when the brake is off (this line is pretty much the switches LED). All of the other lines behave differently and either dont drop in voltage, or drop from 14v to maybe 12v - none drop to ground. This W/G seems to be the most viable given its also part of the system that blocks drivers from watching videos while driving.

The goal: I basically need this line to cut off access to a line that I have wired to the accessories of the car. Thus if the parking brake is on, the device thats triggered by accessories is disabled (no power).

I have tried simply wiring a relay to this W/G line and passing the accessories through it, but this was before I found out that W/G does not ground itself, rather it drops voltage.

Now upon googling this issue I came across this forum and the aforementioned thread.

I have bought the same if not similar components and I wish to assemble this as soon as possible.

The problem then is that I have limited time and thus I cannot just 'figure it out' or quickly learn. I honestly need somebody to show me what to do, to solder what to what etc.

I do know how to solder and in fact do quite a lot of it, but I am not familiar with this type of electronics work, which is quite embarrassing (I do reworking mostly).

Anyways I hope I haven't left something out. I would really appreciate any help.

 

[Diver300]

I suggest that you wire a relay with the coil between the white/green (W/G) and the grey (Gr) wire on the EPB control switch. You should have as small a 12 V relay as you can find, to have as small a coil current as possible.

To start with, just wire in the coil. Don't connect the contact. Then operate the EPB and see if the relay operates, and it the voltage across it's coil goes from nothing to around 12 V.

There is a wire that goes to the existing audio equipment on the car. (It's probably only one wire either *1 or *2 but not both. Car circuit diagrams often show multiple wires when they are alternatives and never more than one on a particular car). That wire will be there to enable or disable something on the audio when the EPB is on. Maybe changing the settings, maybe an entertainment screen.

With the relay in place, check that whatever it is that the audio does in response to the EPB being set still works.

If the audio still responds the same, and the relay operates in response to the EPB, and the EPB light works, you can wire anything you want to the contacts of the relay. You probably want to wire the power to the accessory via the COM and NC terminals of the relay contacts.

If the audio or the EPB light is affected by the relay coil, or the relay doesn't work, it's quite likely that the VDC CM (I've no idea what that is) isn't powerful enough to drive your relay and some other solution is needed.

 

[Insipid]

I suggest that you wire a relay with the coil between the white/green (W/G) and the grey (Gr) wire on the EPB control switch. You should have as small a 12 V relay as you can find, to have as small a coil current as possible.

I experimented with a relay in multiple configurations and I ended up with this (4 pin):

86: Accessories line (12v when car is on)
30: Accessories line again
87: The device I need powered on/off with EPB
85: W/G on the EPB switch plug

This did absolutely nothing, but if I manually grounded 85 it would work. Basically this fails to function with a relay given that the W/G does not ever ground itself. I just need a solution that interprets 0.2v as ground and the relay would function. Hence maybe a mosfet or something between W/G and the relay?

The W/G line is the same one that turns off the video when the car is in motion:

https://imgur.com/CXKrZ6D

So its frustrating I cannot use it in a conventional relay. I am that desperate I bought a mosfet with no real idea of how to wire it all up.

I am also curious if there is some OTHER circuit I could wire to that a relay would 100% work on, but in my experiments that whole EPB switch seemed to be fruitless. Couldn't I just cheat and wire directly to the actual LED or its resistor or something? Surely that would actually have some different effect?

 

[Diver300]

The circuit for the EPB warning light makes it look as though something is grounding the W/G wire. However the thing that is grounding it may not be able to drive enough current to run a relay.

As a result a MOSFET would be one way to go. Which one have you got?

 

[gophert]

2am in Australia now, either it is fixed or not fixed for Monday inspection. Kind of a Schrödinger's cat scenario.

 

[Diver300]

2am in Australia now, either it is fixed or not fixed for Monday inspection. Kind of a Schrödinger's cat scenario.

I had notice the country and the time there. I won't feel hurt if there's no reply today. I hope Insipid won't mind if he posts anything else in a few hours and I don't reply.

 

[Insipid]

I have to get it done pretty much within 24hours of now (roughly)

My shopping list:

Mosfet SUP53P06-20 P-CH 60V 53A (the lowest amperage available)
Diode 1N4007 1000v 1A
Resistor 0.5w 100 ohm
Resistor 0.5w 100k ohm
4pin Relay with 30a fuse
5pin Relay
Alcohol to numb the pain

I have a spare vehicle should I need to go out and buy more, but my local electronics store is kinda sparse (jaycar.com.au)

The car is in the shop getting its mechanical side compliant so I have my bench power supply to test up and prepare for install this afternoon.

 

[Diver300]

That's what I think you will need. The circuit is very quick and dirty, but I think it is what you need. I would add more things like transient suppression if there were time.

The band on the 1N4007 represents the cathode, which the line end of the symbol, the one I have connected to pin 86 and the Drain of the MOSFET

You connect the relay contacts 87A and 30 in series with the thing that needs to turn off when the park brake is on. I've not shown the wires that go to it. You need the 5 pin relay for it to work that way.

The MOSFET is a P-channel one, so the source is connected to +ve in the normal arrangement. When the handbrake is on, the gate is pulled low, and the MOSFET (and the warning light) turn on. That turns on the relay, which opens the connection between 30 and 87A, stopping whatever it is that you need stopped.

When the handbrake is off, the gate is high, the MOSFET turns off, so the relay is off, and 30 and 87A are connected.

If the relay stays on the whole time, check the voltage between G and S on the MOSFET with the park brake off. That should be less than 2 V. It might help to connect a 1 kOhm resistor between G and S. That is in parallel with, so don't break any of the connections in the diagram, just put the resistor there as well.

I hope this helps.

 

[Insipid]

Oh you're a legend. I'll give it a try on the bench (I can simulate 0v by just disconnecting the power?) and then on the car tonight.

So why a 5 pin relay when its only using 4? Or shouldn't I ground the other one?

I dont ground the MOSFET? Well I suppose its getting ground, just thought it would from the one in the back.

 

[Insipid]

I hope this helps.

MISSION SUCCESS!

Mate! Thank you so much! It works flawlessly! I added a switch to the 87 & 30 lines (so between accessories and the device in the boot) so I can bypass this whole ordeal if need be. But so far it works great!

I have had numerous auto electricians have absolutely no idea, or even tell me its impossible due to the CANBUS system.

Have you got paypal/bitcoin so I can make a donation or something?

https://imgur.com/a/Yul51vI