Switched 12V for Dashcam

I thought I'd share my weekend project as I've read a few dashcam threads from folks struggling to find a switched 12V source in the overhead compartment (there isn't one) or hesitant about running a wire up the side pillar and interfering with the curtain airbag. My Prius is a 2006 i-Tech (as it is called in Australia) which has a microphone in the overhead compartment, so if your car has one too then this might help if you're looking for a switched power source for a dashcam or some other device. If this is old news and is already covered somewhere else in the forum please shout out as well.

To cut a long story short, there is a switched 5V source on the circuit board in the overhead unit that I used as a trigger for a relay to switch the 12V from one of the overheads lamps. The switched 5V is located in the centre of the circuit board on the little connector that runs to the small black microphone box. Why not just run a dashcam directly off that 5V? I suspected the microphone wouldn't be too happy about a dashcam drawing 200-400mA away from it so I avoided that option. Feel free to give it a go if you want.



I soldered wires from the 5V source to the input of a relay board (similar to an arduino relay breakout board). Then I soldered straight onto the +12V lamp terminal to a 1A slow-blow fuse and then to the normally-open input of the relay. Note: I removed the passenger side lamp so now the passenger side lamp switch can be used to turn the dashcam on and off. The downside is obviously no lamp - but I don't mind, and I'm sure if you wanted to keep the lamp you could fit it in somehow.



The 12V then runs from the relay to a 12V-5V DC-DC converter. I used a little buck converter board I had from another project (OKI-78SR-5/1.5).



After a bit of testing I packaged the components in small enclosure and shoved it into a gap in the roof space. Bob's your uncle. Note: the 5V is switched immediately on ignition however after the ignition is switched off there is a delay before the 5V is switched off - I timed it at around 42 seconds.



It's is a rough-and-ready solution using mainly parts I had lying around or salvaged from other projects but seems to be working well so far. Of course there's more than one way to skin a cat so if anyone has suggestions please share. If I run into any problems I'll post them here too. Cheers!