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I have to permanently check a certain steel beam if it is fracturing (hair fractures) for that I plan to employ conductive paint and some electronic device that will sound the alarm if and when this connection via the paint is broken i.e. a hair fracture appears. Can someone point me to a simple setup? This is in a 12V DC environment but I could make USB available. thanx -sam

Are you sure the paint will break and not simply stretch over the gap? If I were doing this I would look into the use of a strain gauge or gauges glued to the beam and the Adafruit HX 711 strain gauge amplifier with an Arduino UNO sequencer or equivalent and appropriate display to tell how much the beam is stretching. This is a lot simpler than it sounds and I've found that it works quite nicely. Also I think it will be fairly low cost.

"Are you sure the paint will break and not simply stretch over the gap? "

pretty sure

https://www.team-bhp.com/forum/motorbikes/187991-welding-defect-royal-enfield-himalayan-frame-cracks.html

also see end of video:

https://www.youtube.com/watch?v=2b04Nrub3Pw

OK I see your point. These are catastrophic failures, not hairline cracks. So paint the line across the anticipated failure area and connect a cheap ohmeter to the ends of the line. Low ohms is OK; when a crack forms the ohmeter will show very high ohms. A cheap mulltimeter on ohms setting would work. I hope this is a test setup and not intended for normal operation; I wouldn't consider a bike like this usable for any normal operation.

You are absolutely right, and in my own estimate 1% of production bikes are affected with this flaw BUT as I live in India the selection of bikes with reasonable price is limited to inland makers. Namely only this one. So not much of a choice there. Thanx for the OHM hint, could have come up with that myself LOL. Of course its OHM that goes to infinite when connection is interrupted. Now all I need is some device that will DO something when this happens, e.g. activate the horn. Any ideas?

Regarding danger: The part that breaks first is the lower connection to the head, the upper one then fails due to overload. Between these two incidents there are some seconds, long enough to bring the bike to a full stop, that is the idea behind this setup.

For a cheap and dirty fix which might work connect the painted strip in series with a 12v relay which has a normally closed contact then use the nc contact to control a beeper or indicator light. Feed this from a 12v source on the bike which is on only when the ignition is on (otherwise you will drain the battery when the bike is not in use). Be especially careful with the painted conducting strip. If it is painted directly on the steel at any point, the steel will bypass any break in the strip. It would be best to put a thick base of insulating paint or varnish on before painting the strip.

I thought about that but decided against it. a relay draws too much current for the paint to support, I would like a digital solution which will draw much less. Is there a ready made thing that could do what I need? some multi purpose part like this? although it says output 240v but that must mean maximal 240v as a switch is should be irrelevant what voltage it switches:

https://www.amazon.in/REES52-Channel-Solid-State-Module/dp/B01KZ14EC8/

I gather from the reference you cite, plus the data sheet for the relay that it is a triac switch as the rating is only AC and not DC and optical isolation. If so it will pick up when the stripe is good but will not drop out on a break--not what you want. Take a look at https://www.adafruit.com/?q=3191 and 2895. These relays are logic level operated and have NO and NC outputs. The only wrinkle is that they are rated 3v so will need a series resistor in the coil circuit and probably a voltage divider in the signal input to bring the 12v down

Thanx for the link, that looks promising. I will look into it!

Just looking through the stuff where I used the Adafruir Featherwing power relay and found I have already made an elementary diagram for it which is quite a bit more informative than the Adafruit documentation. If you could give me an email address I can send it to you in .pdf form.

that would be appreciated! g.kossatz@gmx.de

thank you !!