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#### FlatButt

##### New Member
Hi, I have a 12 volt dc circuit that has two (2) separate 12 volt positive inputs and two (2) separate 12 volt negatives. Both positive and both negative inputs are from the same 12 volt vehicle source (circuit 1 is switched via my vans ignition), (circuit 2 is manually switched via a toggle switch) and both are used to feed a 12v to 5v USB converter at 1.5 amps which powers an Xplore C+1 Dash Cam.

I need ALL of the feeds (the 2 Pos + the 2 Neg) to be isolated from each other so that one circuit (supply) does not feed the other at ANY time.

Should I put Diode protection on ALL four leads? (2 positive and 2 negative)

The normal circuit (1) is powered via the the ignition and is for my Dash Cam when the van is in motion.

The second circuit (2) is powered from the fuse box (currently switched on/off by toggle) which is going to be replaced with a remote controlled switch, so I do not need to enter the van to switch the toggle on/off for downloading the recorded images.

The Camera uses WiFi to download the recordings to cellphone and or tablet via an Android App and decode the recordings and GPS data.

Which can not be done on a PC as the camera operates on its own specialised Android App and is painfully slow to download and convert each 3 minute video recording. In order to retain the GPS data the Android App must be used. Removing the mini SD card and transferring the video to PC does not give the GPS data.

I will be replacing the toggle switch with a remote controlled switch, which I have. But it ONLY switches the NEGATIVE circuit leaving the Positive uncontrolled (hot) and this is my concern with back feed.

I WILL be using diode protection to stop the 12 volt positive feeding back into the ignition and vice versa into the remote switch via the fuse box. I feel that I should also be using diode protection on both of the negative sides as an extra precaution.

Should I use diode protection on both the positive and the negative leads (of which there are 2 of each) or just the 2 positive inputs?

#### KeepItSimpleStupid

##### Well-Known Member
Dash cam needs 12v from ignition when I am driving and 12v from remote controlled circuit when I am out of the Van.

This is really the key.

Your **broken link removed** if that's correct is basically a relay.

So, the CONTACTS are ISOLATED.

The 12 V receiver would therefore have to powered all of the time from a BATT connection.

Your relay, would put the C (Common terminal) to the Dash Cam.
The (NC) or normally closed connection would go to the IGN side. Whatever is powered when the ignition is on. The NO or Normally open side would go to the BATT connection. You have to change your thinking a bit. The common terminal feeds the device, not the NO or NC terminal. It totally solves your isolation problem. No diodes necessary. If you would like, you can place a properly sized TVS (Transient voltage suppressor) at the dash cam side.

It used to easy finding those connections. These days, I have no idea.

Aside:
Since there is no feedback or two-way communication, what you might do is figure out a way to say activate the lights/horn or whatever. e.g 1 blink on, 2 blinks off.
A 2-hour timer or whatever would even be better.

You did a MUCH BETTER job describing the problem this time. I hope I did too.

FWIW, the car "used to" have an ON bus and an ACC bus. The ignition switch used to tie these together. Now it's difficult to determine if the engine is running. You almost have to use the CAN bus within the automobile. Flashing the tail lights like I suggested might also be nearly impossible.

Your image download may not be WIFI. Bluetooth makes more sense. That's immaterial.

Did you check the range? You may only have about 30 feet.

#### Diver300

##### Well-Known Member
I agree with KeepItSimpleStupid, in that the modules from ebay have a relay output, and using the three terminals as described means than no diodes are needed. He didn't say that the negative of the dash cam converter needs to connect to negative permanently. Also the +ve and -ve supplies to the remote switch need to go to a permanent supply and to ground respectively. Those two are connected to the NO and to the -ve of the dash cam, so you still only need three connections from the car, ignition, permanent and ground.

I think that the remote switch will take about 10 mA when the output is not energised. Just running the relay when the output is energised will take more like 150 mA. Although the camera will take less than 1 A average, you should make sure that you turn off the camera or the drain will kill the car battery over a weekend.

#### KeepItSimpleStupid

##### Well-Known Member
you still only need three connections from the car, ignition, permanent and ground.

Ignition = the circuits on when the engine is running or the ACC position. (Powers the dash cam when selected)
Permanent(= Circuits that are on all of the time; The battery. (powers the receiver; Powers the dash cam when selected)
Ground = the negative terminal of the battery. (permanently connected to dash cam and receiver all the time)

ACC is not the position of the ignition switch. It's the circuits activated by the ignition switch in ACC and ON positions. i.e. Radio

ON would include the turn signal circuit, back-up lamps etc.

The quiesient current of the receiver needs to be small.

As Diver and I both suggested, you need to somehow know the camera is off. If you can't connect, that might be enough.

#### FlatButt

##### New Member
Cheers and Thanks to KeepItSimpleStupid and Diver300. I have been trapped in a time warp for far too long. (old way of thinking) and yes the Remote is also a relay.

Thanks for clearing the junk from my mind. I guess that the accident that left me chairbound ahs also left part of me in the past.

Cheers and Thnaks Guys.

#### Les Jones

##### Well-Known Member
None of the results that I looked at from a search that you suggested on ebay say that the unit could only switch the negative line. They all seem to have two connections for the twelve volt power supply and another three connections to the changeover contacts on the relay. If you look at **broken link removed** you will see a diagram of it switching the positive to a lamp. I have two of the four channel versions of these remotes. Their standby current is about 8 mA and when a relay is activated they take about 50 mA. The standby current of the single channel one will probably be the same as the 4 channel version. On my 4 channel units each relay provides a floating set of changeover contacts. If you provide a link to the ACTUAL item on ebay the I may be able to see why you think it can only switch the negative wire. If the 12 volt to 5 volt converter that you are using is the most common type you see sold in the £ shop chains (And elsewhere.) then these normally use a an MC34063 switching regulator chip (Or similar.) Which would work with th input voltage as low as 8 volts. This means that any normal diode such as a 1N4002 could be used instead of one of the more expensive schottky diodes.

EDIT.
I have just noticed some more replies have been posted while I was typing (Ind testing the current consumption of the 4 channel remote.) The point made about not knowing if the unit was left switched to the on position is a good one. If you used a 4 channel unit (Or probably a 2 channel one if they are available.) then they can be configured so that one button switches the relay on and another button switches it off. (In this mode only 2 of the 4 channels can be used.) I use one of the 4 channel units to switch on lights on our gate posts so We can see them better when reversing in at night. I have also added a timer so it switches off after 5 minutes if we forget to switch it off wth the button.

Les.

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#### Les Jones

##### Well-Known Member
In your link in post #15 the last picture shows that the relay contacts are floating. The positive input can be linked to the relay common with a blob of solder bridging the tracks neat the positive input.

Les.

#### KeepItSimpleStupid

##### Well-Known Member
In your link in post #15 the last picture shows that the relay contacts are floating. The positive input can be linked to the relay common with a blob of solder bridging the tracks neat[sic near] the positive input.

Les.

It can. But why? Common needs to feed the Dash Cam. The dash cam needs power from two different sources. It's the common point.

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#### Diver300

##### Well-Known Member
In your application the Dash Cam needs to be switched from one feed to the other. That is not so usual. In most cases, there would be an output to be switched on, so connecting the common to +ve would work with the load connected to NO. In other cases there could be an output to be switched off, where common would be connected to +ve and the load connected to NC. So for nearly all uses, common can be connected to +ve, and the manufacturers have made that easy, but they realise that there are other uses that they won't have thought of so they let you remove the link and use the relay as you want.

#### FlatButt

##### New Member
OK, here is what I THINK I need to do. Please correct me if I am wrong (which is quite common) I have had to upload as a MS Word Doc as for some reason I could not upload as a JPG or PDF.

#### Attachments

• Doc1.doc
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#### KeepItSimpleStupid

##### Well-Known Member
Sometimes the forum software is picky with extension case, but .pdf in lower case should have worked. It could be a case sensitivity. We know it happens in Linux. Basically you can't find the file to upload.

Looks good. You didn't label the top red wire. Should go to battery.

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