Help me check my relay wiring?
Posted by punkassjim@reddit | projectcar | View on Reddit | 26 comments
Currently I've got an Android head unit and an aftermarket reversing camera. There's a signal wire between the head unit and the camera, which also patches into the reverse bulb circuit, which acts as a trigger. When voltage goes to the reverse lights, it triggers the camera to pop out, and the radio to switch to camera view.
I've added a button on my center console to switch on the reverse camera anytime I like. But, importantly, the reverse lights must not light up unless the car is actually in reverse. Please check this diagram and see if I'm missing anything important?
jeristair@reddit
Replace the relay with a diode. Way simpler.
There will be a 0.7 V drop across a standard power diode, but it'll be fine. A Schottky diode could also work.
punkassjim@reddit (OP)
Oh actually, I think I had considered using a diode but was concerned that the reversing lamp voltage would also be fed back into the switch when it’s not switched on. Would this cause an issue? Or would doing it with two diodes be a good idea:
jeristair@reddit
The second diode going to the switch is unnecessary, as when you're in reverse, the orange portion of the wiring would have 12v on it but the switch (not drawn) would be an open circuit. If this switch is reused from something else (Or if there are other things tapped into the same switch) then yes the second diode is necessary to prevent backfeeding.
punkassjim@reddit (OP)
The switch is one of these guys.
The two blue wires coming out of the button are the signal wire and the voltage input for the "this switch is on" yellow LED inside the button. I've got the two wires soldered together, so when the button is pressed, the signal wire lights the LED.
So, yes, the switch circuit is technically open when it's not pressed. And if I only use one diode, that'll mean that putting the car into reverse will automatically illuminate the yellow LED inside this button, regardless of whether the button is pushed or not.
And honestly, I can't see any problem with this. Can you? As long as the CECM doesn't have any CAN bus errors from the bulb monitoring, I'm satisfied. And the parking camera button illuminating on its own seems kinda neat.
Any_Squirrel@reddit
Is there a way to run 2 camera inputs(splitter) into a single camera feed on the head unit? Camera 1 is regular backup cam, reverse switch triggers radio, power is fed to camera off back up lights. Camera 2 fed off left turn signal pre-flasher unit powering both camera and triggering head unit?
I suspect the trigger circuit would need a relay, and you would potentially end up with problems if both backing up and using left hand signal(unless ofcourse there’s a way to tell the relay IF left + backup = no power to camera)
jeristair@reddit
This could probably be done with relay and diode logic. But I think a module like this might be the better way to go. From my understanding, the master VIN is wired straight to Vout, and when power is supplied to the ACC, it switches to the slave VIN. This would sort out the camera switching. The way I'd wire this if my understanding is correct, is to have the camera 2 feed into the master and then reverse feed into the slave. The ACC wire would go to the reverse lights, so whenever the reverse lights are on the feed will always switch to the reverse feed if that is the preference you want. Then the last thing to sort out is the power signal to the radio. So both camera 2 feed and reverse lights signal would need to go through separate diodes to prevent backfeeding, then the one signal go to the radio. So the two diodes would point at each other like in punkassjim's image above.
Any_Squirrel@reddit
Sweet thanks!
punkassjim@reddit (OP)
Ayyyy, that's the kind of insight I was hoping for! Thanks, I'll look into that.
66NickS@reddit
Your wiring diagram is incomplete/not quite right. At the very least it’s missing your incoming power and it’s unclear how things are grounded.
I think what you actually need is to have the gear selector do its normal thing for the radio and camera, with a separate wire to the reverse lights. Then you need a manual switch to the camera and radio that doesn’t also connect to the reverse lights.
punkassjim@reddit (OP)
Sorry, I figured people could understand the voltage sources just by looking at the words. The CECM supplies voltage to the reverse lights, and the switch (button, whatever) also has a voltage output. You don't have to worry about the grounding for anything but the relay, and I used a standard symbol for ground. It's the brown lines.
* The gear selector is not currently wired into the radio or camera, hence the signal is being taken from the reverse light. That's not going to change.
* I do have a manual switch. It's in the diagram.
* The relay is switching between those two power sources, thereby removing the reverse light circuit from the camera circuit when the button is pressed.
So, if this diagram doesn't do exactly what you're saying it should do, please explain why.
66NickS@reddit
Ok, I see what you’ve got set up here. So what you need to switch is to have 87A go to a constant B+ and then your manual switch is only wired to 85 and switches B+ on/off.
I guess you could leave it as is, but that kind of defeats the purpose of the relay.
punkassjim@reddit (OP)
> So what you need to switch is to have 87A go to a constant B+ and then your manual switch is only wired to 85 and switches B+ on/off.
The camera only requires a low-current signal voltage, and the relay itself doesn't require much current to activate. So, what problem does it cause to feed the same signal voltage to both 85 and 87a?
* When the button is off, the relay is not energized, and the camera only turns on when the reverse lights send voltage through circuit 87.
* When the button is on, the relay is energized and the camera is turned on by the same 12v source that energized the relay.
> I guess you could leave it as is, but that kind of defeats the purpose of the relay.
Please explain what you mean.
66NickS@reddit
The purpose of a relay is to have the power go from B+ through the relay and to the component, bypassing the switch. Since this is a relatively low power/current device it’s probably not a big deal, but it’s just not “normal” to have the switch wired to two legs of the relay.
You could theoretically remove the relay and have an “a/b” or “on-on” switch. So 2 inputs and 1 output. Input one is your default and when you shift to reverse it activates everything. Input 2 is your manual on. Basically the switch becomes the relay’s switch between 87 and 87A.
Again, your diagram should work it’s just not the way it would normally be done.
punkassjim@reddit (OP)
There's a number of ways to wire a standard relay to accomplish different tasks. Seems like you're only familiar with one of those ways.
66NickS@reddit
Good luck man, I was just offering you some advice and tips on alternatives. Clearly it struck a nerve.
punkassjim@reddit (OP)
Oh I'm not bothered. I just don't hesitate to tell someone when they don't understand things as well as they think they do. ¯\\\_(ツ)\_/¯
DEWGONGsdong@reddit
Insult deleted
nastonius@reddit
Okay. So if I understand right, you want to use the reverse light bulb power (power when the reverse lights are on only), to trigger the camera to pop out and the head unit to display the camera feed.
You also want to use an auxiliary switch to turn the camera and the head unit display on whenever you want WITHOUT activating the reverse lights.
Does that sound right? I want to make sure I understand your question before I make a recommendation on a relay setup.
My first look at your diagram in the post says to me that your wiring won’t do what you want, wired like you have drawn.
Fearlessleader85@reddit
It's a bit of an odd way of doing it, but it actually should work. When his switch is off, the relay is in the normal mode of giving the reverse light switch control of the camera. When the new switch is on, it both energizes the relay, disconnecting the reverse light circuit and switching the camera.
punkassjim@reddit (OP)
Thanks! Can you say more about what's odd? I'd be happy to hear if you think there's a simpler way of doing it!
Fearlessleader85@reddit
I don't know that it's simpler, but normally the power for the relay wouldn't also be the power THROUGH the relay. So the switch would run only to the relay solenoid and you would bring a keyed 12V signal straight to the second pole on the relay. For your usage, i don't think it makes much difference.
punkassjim@reddit (OP)
Yeah, if this relay were powering a motor or something that draws significant current, I'd be more concerned about sharing that voltage feed. But the reversing lights are LEDs and the relay itself doesn't draw much current, so I figured it might not be an issue. Does that seem correct?
Fearlessleader85@reddit
Yeah, i don't think it will matter, because it's essentially just signal voltage, right? It's not even actually powering the camera, just telling the head unit when to show the camera, yeah?
punkassjim@reddit (OP)
Not quite, but let me try to word it more accurately:
## The way it works now (which is not what the diagram above shows):
* There's a signal wire between the radio and the camera.
* This signal wire also makes connection to the reverse light.
* When the reverse lights illuminate, this voltage triggers the camera to flip open, and the radio to display it.
## The way this relay diagram would change things:
* If the button is NOT pressed, the camera operates exactly as it does in the above section (see Circuit 87).
* If the button IS pressed, the reverse lights are no longer connected to the camera trigger circuit.
* If the button IS pressed, the relay and the camera circuit are *both* energized by the voltage output from the button (see Circuit 87a).
If this seems clear, and you still don't think it would work, please explain why.
RunV5@reddit
I dont quite remember which relay pole is normally switched to but i think 87 and 87A need to be switched but other than that I beleive it would work
punkassjim@reddit (OP)
Not quite, but let me try to word it more accurately:
## The way it works now (which is not what the diagram above shows):
* There's a signal wire between the radio and the camera.
* This signal wire also makes connection to the reverse light.
* When the reverse lights illuminate, this voltage triggers the camera to flip open, and the radio to display it.
## The way this relay diagram would change things:
* If the button is NOT pressed, the camera operates exactly as it does in the above section (see Circuit 87).
* If the button IS pressed, the reverse lights are no longer connected to the camera trigger circuit.
* If the button IS pressed, the relay and the camera circuit are *both* energized by the voltage output from the button (see Circuit 87a).
If this seems clear, and you still don't think it would work, please explain why.