DC Voltage level sensing

If you can find the fuse block (I've done that) and probe it (almost impossible, my car hasn't enough room for me to get my head where I can see the darned thing without a mirror in one hand, which leaves my other two hands free for the flashlight and the meter probe), then you can look for an unpopulated fuse position, and tap in there.

Or, splice into the radio power wire, which means sharing the fuse capacity of the radio. Some radios have more than one power lead (one for the clock).

TL341 seems rated for automotive use.

I suspect that he wants to tap into the dome light circuit (which is always hot and is available near the rear-view mirror mounting in many cars)

Otherwise It's easier to tap into the accessory or ignition circuit behind the dash, and not bother with sensing anything...

It's typically in the steering column, and in the fuse panel, also at the back of the radio etc... the wiring diagram for the automoibile in question will have all the answers.

Any comparator will do, but you need a LOT of filtering in a car as the battery voltage is not clean.

I would use a PIC, as most have and ADC and 2 hardare comparators. But any 12V or so opamp will do.

The PIC would also display battary voltage..

Eye wrote ..Any comparator will do, but you need a LOT of filtering in a car ..as the battery voltage is not clean.

Hysteresis, I forgot hysteresis, else your -cam will flapper on / off.

Why do you want the dashcam to work only when the engine is running? If you are parked listening to the radio, setting the satnav, or whatever with the engine off, and somebody drives into you, wouldn't you want that recorded?

My dashcam plugs into one of the USB sockets on my car, and operates (as others have suggested) when in "Aux" mode without the engine running. If possible I suggest you do the same.

mandag den 11. november 2019 kl. 03.00.57 UTC+1 skrev snipped-for-privacy@notreal.com:

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OBD-II only specifies an always on +12V battery, though I believe audi/vw p uts ignition ON on one of the unused pins

It was so much simpler in the 'old days' when you had access to the rotary switch behind the ignition lock. Unfortunately, the vehicle in question is one of these 'keyless ignition' types that neatly removes that option. And they label all these unnecessary and undesirable changes as "advances"!

I wish. Not with modern cars. Trying to get behind the dash is a nightmare and could even be seriously injurious if the airbags behind it get accidentally triggered in the process!

PS 2 When I drove my LPG car the solenoid that opened the tank were controlled by the drive to the ignition coil. As long as there were pulses there, the liquid gas could flow. A much better way, engine stopped -> camera off.

Simple circuit too, only needs one transistor and a relay

This is what Win suggested earlier and since these are simple to configure and cheap as chips, I intend to go down that route for the sake of expediency. The cig lighter sockets on this car are 'always on' so to speak so there's another good reason.

No, sorry, not Figure 25. Although this is a perfect application for a TL431, none of the figures in any of the datasheets show it. Here's the circuit I had in mind, time for an ASCII drawing:

. turn-on output, if Vin > Vp . . --+--- S D ---- switched Vout . | G p-channel . | | MOSFET . +- R3 -+ pass voltage Vp: . | | Vp = 2.5 (1 + R2/R1) . R2 | R1 = 2.49k . | K R2 = R1 ( Vp/2.5 - 1 ) . +-- REF e.g. R2 = 11.0k for 13.5V . | A TL431 . R1 | R3 = 3.3k pullup . | gnd . gnd R2 could include a trimpot

Yep, you had the temerity to criticize P.A., and as predicted, that set him off on a rant. Haha, now he'll probably go after me as well. But unlike P.A., at least I posted a useful circuit, with formula, for my suggestion.

Win, did you create this in plain text, because for the life of me I cannot get it to render correctly this end, not even when trying 3 different text editors and different fonts. Just wondering if you accidentally got some formatting in there or something?

# # turn-on output, if Vin > Vp # # --+--- S D ---- switched Vout # | G p-channel # | | MOSFET # +- R3 -+ pass voltage Vp: # | | Vp = 2.5 (1 + R2/R1) # R2 | R1 = 2.49k # | K R2 = R1 ( Vp/2.5 - 1 ) # +-- REF e.g. R2 = 11.0k for 13.5V # | A TL431 # R1 | R3 = 3.3k pullup # | gnd # gnd R2 could include a trimpot #

It's simple mono-spaced, fixed-pitch, non-proportional ASCII text, which is the original standard for usenet. I can see it fine with NewsGuy on both of my computers. Hopefully your newsreader doesn't munge the text, by removing lines, symbols, spaces, periods, etc. If it behaves, you can copy and paste it into notepad, or some other editor. If I paste it into Word, I have to then select the text, and change the font to courier.

Google Groups displays with a proportional font. I brought this post up in Google Groups, then copied and pasted into notepad, and it came out fine. Try that.

Jan suggested a filter, add a cap across R1. And he suggested hysteresis, add resistor R4 from the R1 R2 REF node to switched Vout, R4 = 1.0M for 0.2 volts.

Thanks, Win (and Jan) I'll do that. For the P-MOSFET, I've got dozens of IRF5305 devices I bought from Farnell years ago. They're hexfets and way OTT for this application, but I plan to use one just to get some more value out of the original purchase!

I've managed to manually re-edit your schematic it's fine now; many thanks indeed as ever.

Post it in LTspice. There will be no problems with pasting fonts back and forth, and we can see it run. You cannot run an ASCCI file.