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I have a piece of a broken camera flash (an old Yongnuo one) that has a single pin that tells the flash when to fire. The pin looks like this :bottom of flash module (I guess the ring is the return/ground?)

The other side of the piece looks like this: circuit side of flash module

If my guess isn't completely wrong, those four wires are the only thing that tell the rest of the flash unit what's going on, when. So if I plugged (two, three, all four?) of those pins into my arduino I could use it as an input, yes?

I.e. Arduino would detect when the camera has taken a picture via this unit, and do something else (in my case open the gate on a mos for a length of time). No actual camera flash involved (just the signal)

My question is: how do I determine which of these four wires carry the signal to the rest of the circuit, and can I plug this into my Arduino input pin? My multimeter is a cheap crappy one so I don't think it would react fast enough to measure a pulse like that...

ajlowndes
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  • First you need to determine how the flash works. Does the camera send a pulse, or does it connect the pin to ground. Try switching the flash on, then when it's charged, use a wire to connect the pin to the ring. If it flashes then you have the equivalent of an active low digital input. You'd need to then know the voltage levels and maybe even isolate the whole flash unit form the Arduino. It's quite a broad question with lots of unknowns at the moment. – Majenko Sep 24 '15 at 11:23
  • huh, i just tested it with one of my working flashes (similar model, and it is a yongnuo one) - and yes the flash (sans camera) is triggered by simply connecting the pin to the ring. So how do i figure out the voltage level? would my cheapo multimeter help at all? Thanks for your help so far, I had no idea that was how the flash triggered! – ajlowndes Sep 24 '15 at 12:09
  • So let me get this clear - you want to have the flash attached to the camera, and add a feed off the flash to indicate to the Arduino when a photograph (using the flash) has been taken? Or do you want the Arduino to make the flash trigger intendant of the camera? – Majenko Sep 24 '15 at 12:15
  • nope sorry I wasn't clear. The flash that I took pictures of above is broken, it won't even turn on. I took it apart and gave up when I saw all the microscopic solder spots that I cannot fix by hand. So it stayed in pieces until now. I now have another project which is a camera slider for timelapses - the camera sits on top of a wooden dolly which is pulled along a track by a bbq rotisserie motor. The rotisserie motor is currently too fast, pulling the dolly along the track in only 10 mins or so, and I need it to be a good few hours, so I need to find a way to slow it down... (cont) – ajlowndes Sep 24 '15 at 12:17
  • Ok, so you want the Arduino to react when the camera would have fired the (non-existant) flash? The pin in the middle of the camera's mounting will most probably be the drain of a MOSFET which is turned on (connecting it to ground) when the camera triggers. Check the voltage (on the camera) between the centre pin and the ring while it's just idle. If there is no voltage showing then that is most likely a safe assumption. You can then just connect the ring to the Arduino's ground and the pin to an input pin. Turn on INPUT_PULLUP and you should be able to read the state. You might want to – Majenko Sep 24 '15 at 12:21
  • ... use one of the interrupt pins so you can react fast enough. If there is a voltage showing between the two pins and it's not 5V then you will have to build some kind of interfacing system to the Arduino, and that depends on what the voltage is. – Majenko Sep 24 '15 at 12:22
  • (cont.) I tried strings and pulleys etc, but they weren't reliable enough. I figure if arduino can detect when the camera fires, then it can turn the rotisserie motor on for a few seconds, before shutting it off again. So I need a way of detecting when the camera takes a picture. I know from previous experience that my camera always fires the flash hotshoe at the end of an exposure (called "rear curtain sync") and I pulled out my box of broken flash bits and found the photographed piece. make sense? – ajlowndes Sep 24 '15 at 12:23
  • You've been a huge help Majenko - thanks so much! – ajlowndes Sep 24 '15 at 12:25
  • I'd just connect the two green wires to the arduino and remove the entire circuit board. That is, if the camera just "shorts" those two contacts to signal a flash-request. However this connection could also be used to detect if a flash is present, so the camera can disable the internal flash. In that case my solution won't work. – Gerben Sep 24 '15 at 14:44

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