I have wired up my vehicle dashcam in a way that when the engine is started, the dashcam starts recording and stops recording when the engine is switched off as it should be.
However, I wanted a seperate switch so that I can keep the camera recording when the engine is switched off, Eg. if I was to get stopped by the police or some other reason and want to keep the camera recording.
So, I added a DPST switch (SW2 in the pictures) under the dashboard and into the circuit to accomplish this. Sadly the other day I somehow switched this DPST switch on (which I didn't notice) but the engine was off, so that the camera was recording and it eventually drained the battery.

I then decided that if I added an LED (D1) indicator so that when the camera is recording the LED will glow. But now I decided I don't really want the LED glowing when the engine is running and camera is recording.
My question - can anyone think of a very simple and easy way I can wire up the dashcam and LED so that the LED glows (and camera is recording) ONLY when the engine is NOT running?
Picture 1 = Normal condition when engine is not running and camera is not recording.

SW1 ignition switch is OFF (engine not running), SW2 is in the A position (camera IS NOT recording)​

Picture 2 = Situation when engine is not running but I want the camera/LED is on. (Eg. Stopped by the police)

SW1 ignition switch is OFF (engine not running), SW2 is in position B (camera IS recording)​

Picture 3 = Situation when engine is running I also want the camera recording BUT I do NOT want the LED on.

SW1 is on and the engine is running, SW2 is in position A and camera is recording BUT I do not want the LED on.​

So basically I want the camera on and the LED to switch off ONLY when the engine is running.

 

Just to clear up a little confusion, you have a SPDT switch. Changing that to a DPDT switch will allow a separate circuit for your LED so that when the switch is in the "Normal" position (engine running or not) the LED does not light. But when switched to the "Standby" position one of the two circuits powers the camera and the other powers the LED.

 

I would install a timer circuit so that the camera will turn off after a given time when running off the battery.

 

Another version using a SPST switch.

 

REally, this is fairly simple. To have the indicator ON only when the camera is powered AND the engine is switched off, and off under all other conditions.
You will need to add a diode in series with the indicator LED, along with the current limiting resistor. The positive connection of this string will connect to the camera package positive connection, the negative end will connect to the ENGINE positive supply from the ignition switch.
This will work because when the engine is switched off, the various powered devices, such as fuel pump, ignition system, alternator system, and fuel injection system, will all present a low resistance to the battery negative connection. Consider that if the total draw is six amps with the engine running, that represents a two ohm resistance, which will not produce much of a voltage drop at the 20 milliamps the LED will draw. So this is the simple, cheap, and easy to provide the indication requested.

 

MisterBill2 version.

 

MisterBill2 version.
View attachment 296137

That is as simple as I can make it. With the engine off, the engine power input is pulled down very close to zero by all of the engine devices. With the engine on both ends of the string at 12 volts so no current flows.
and Thank You to sghioto for presenting the circuit drawing.

 

If a DashCam ran your Battery down,
then You need a new Battery.
.
.
.

 

Just to clear up a little confusion, you have a SPDT switch. Changing that to a DPDT switch will allow a separate circuit for your LED so that when the switch is in the "Normal" position (engine running or not) the LED does not light. But when switched to the "Standby" position one of the two circuits powers the camera and the other powers the LED.
View attachment 296131

Yes of course. Thanks. This is what I wanted and very easy, I was just having one of those blank moments!

 

I would install a timer circuit so that the camera will turn off after a given time when running off the battery.

Yes, I could thanks for the suggestion but I don't usually forget. It was just one of those days!

 

REally, this is fairly simple. To have the indicator ON only when the camera is powered AND the engine is switched off, and off under all other conditions.
You will need to add a diode in series with the indicator LED, along with the current limiting resistor. The positive connection of this string will connect to the camera package positive connection, the negative end will connect to the ENGINE positive supply from the ignition switch.
This will work because when the engine is switched off, the various powered devices, such as fuel pump, ignition system, alternator system, and fuel injection system, will all present a low resistance to the battery negative connection. Consider that if the total draw is six amps with the engine running, that represents a two ohm resistance, which will not produce much of a voltage drop at the 20 milliamps the LED will draw. So this is the simple, cheap, and easy to provide the indication requested.

Excellent, thank you MisterBill2

 

If a DashCam ran your Battery down,
then You need a new Battery.

Fortunately the battery is ok. The car was in my garage for 2 or 3 days with the camera recording but I didn't notice. I've never done that before and I couldn't work out why I couldn't start the car!
That's why I thought I need a LED light so that I would notice the camera is on when the engine is not running.

 

Thanks everyone for your very good suggestions!

 

By now you have sufficient answers to solve your question. Here's one I drew up; actually there are two versions here. The thinking on this one is when I go to the store and someone bumps my car. That's happened on a few occasions now. Some cam's come with a collision sensor that will automatically record. But in many cases that has resulted in dead batteries - or so the reviews have said. MY solution was to have a camera record during the entire time I'm in the store. Notice the relay is grounded through a brake light. There's sufficient current through the bulb to hold the relay active. Also notice that the relay (right version) can hold itself active. HOWEVER - as soon as the brake pedal is pressed the relay now sees power on both poles and has virtually no current to maintain a lock, and the relay drops out. So if I park, activate the relay, then shut the engine off - notice it takes a specific set of events to lock the relay and cam on - the camera remains powered after I shut the engine off. So the camera records until the next time I step on the brake pedal. But by then I'm back in the car. If someone bumps my car - I'm right there.

So the camera has shut down when I stepped on the brakes. But then I start the engine and the cam is powered via normal operating mode. So I don't have to "remember" to shut it off. When I get home I don't need to record the goings on via the dash camera, I have security cameras to do that.

In the left hand version there's a latching relay. When powered it latches the camera on. It takes a brake pedal signal to deactivate it. The sole purpose of the diode is to prevent back-powering of the auto electronics. And the slight drop in voltage will not affect the camera whatsoever. ALL switches are momentary. Personally, I think the latching relay setup is better. The relay doesn't draw power except only for the moment it is latched or unlatched. All other times there is no current passing through the coil. And no, I haven't built this yet. It's one of those "other" projects I hope to get to soon. The difference is that with the latching relay you don't necessarily need the engine running to start the latch camera. You don't even need to connect it to an ignition active circuit - you can go straight to the battery, so it can be started any time. The right hand circuit requires the key to be on to activate the relay.

 

Here's a third version, this one doesn't require the key to be active. Having been messing around with the drawings, I like this one best. Two features: First, the key doesn't need to be active to start the circuit, so you don't have to remember to turn it on before you shut the engine off, and the second feature is you don't have to remember to shut it off. As soon as you step on the brake pedal - it's off. Unless the key is on, then the camera operates in normal mode. There MAY be some heating issues with the brake light signal heating the relay every time you step on the brakes. But a small resistor should be sufficient to block excessive current from heating the coil while still allowing enough current to reset the relay. The additional diode and "Cam Stop" switch allows you to shut it off without having to step on the brake pedal.

 

Another version using a SPST switch.
View attachment 296133

Thanks sghioto, this is a good idea but I'm not sure, the diodes will have a voltage drop which may have a detrimental effect on the operation of the camera. I will have to test this. So far I think Tonyr1084's suggestion is the easiest and simple to implement with just a DPDT switch.

 

Thanks sghioto, this is a good idea but I'm not sure, the diodes will have a voltage drop which may have a detrimental effect on the operation of the camera.

The camera operates on 5V, which is supplied by the camera power supply. The supply can easily run on 10 to 15 volts. The diode Vf will not affect the camera's performance. Auto Voltage varies throughout the running cycle. A good battery will have a resting voltage of around 12.6 volts while a weaker battery - after startup - may see voltages as high as 14.5V or even more. Typically with a good battery, when the engine is running, the voltage floats around 13.6 to 13.8V. Vf will have no effect on performance.

 

The camera operates on 5V, which is supplied by the camera power supply. The supply can easily run on 10 to 15 volts. The diode Vf will not affect the camera's performance. Auto Voltage varies throughout the running cycle. A good battery will have a resting voltage of around 12.6 volts while a weaker battery - after startup - may see voltages as high as 14.5V or even more. Typically with a good battery, when the engine is running, the voltage floats around 13.6 to 13.8V. Vf will have no effect on performance.

Oh yes, that's true....good thinking