Simplest solution to automatically turning off dash cam when ignition is off, but turn it on with button?

Question

I recently purchased and installed a dash cam in my vehicle (large truck). It requires three connections: ground, constant ~12V, and ignition/accessory ~12V. I have connected the dash cam to appropriate fuses in my fuse box with "add-a-fuse"s. When the ignition is on the dash cam records, when the ignition is turned off the dash cam records either for a specified time, until a specified battery voltage from the constant 12V is read (range for this threshold is 11.9-12.9V), or not at all. I have been utilizing the timer based shut off for a week. My vehicle provides a dash readout for the battery voltage. Over the course of the week the voltage dropped from ~14.8V to 13.9V. I assume if I had continued using this timer function I would inevitably drain/destroy the battery. Since then I have unplugged the dash cam after parking the vehicle. Over the next few days of driving the battery voltage got back to the ~14.5V range.

I do not need or want to record my parked vehicle every time I park. I only want really want to record while parked when going and parking in small cramped public lots or "sketchy" places. I don't do either very often. As a result, I end up plugging and unplugging the dash cam every time I enter and exit the vehicle which is growing quite tedious. What I would like is a mechanism to turn off the power to the camera when the vehicle ignition is turned off along with a momentary pushbutton to turn it on, while parked, to record. This way I don't have to worry about plugging/unplugging and if I park in some public lot or sketchy place, I can just tap the push button as I get out and the camera goes into record mode (using its own timer or voltage cutoff thresholds).

I think I can achieve this with a relay and latching button. The relay would be placed on the ground line and normally open. A branch from the ignition line would be used to trigger it. The button would be connected to a branch from the constant line into the relay. This would in effect provide the 4 states I require.

1. Parked: No power on the ignition line so the relay is open and no power to the camera (simulates unplugged).
2. Driving: Ignition is turned on so the relay closes and the camera turns on (simulates plugging in).
3. Parking: Ignition is turned off so the relay opens and the camera turns off (simulates unplugging).
4. Surveillance: The button is depressed so the relay closes and the camera turns on (simulates leaving camera plugged in after parking). The camera goes into its standby recording mode because it only sees constant and ground but no ignition. It records based on its settings and turns itself off. When I get back in the car I must depress the button again to its open state.

Does this seem correct? Is there a simpler solution? How can I go about sourcing the correct relay and button?

Answer 1

Here are a couple of options.

Option A: It looks like the ignition wire acts as an inhibitor that keeps the camera from recording when it has 12v. You could use a switch (SPDT) to connect it to 12v when you turn off the ignition so the camera does not record. Make sure the switch can handle the current needed.

Option B: You could use a switch (DPST) to just disconnect the 12v and ignition wires from the camera. This is what you do when you disconnect the camera anyway but simpler. Again, make sure the switch can handle the current needed.

I Hope that helps.