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I want to build my own external flash/ledlight/softbox just for practice and knowledge. What pin gives signal to external flash before a photo is taken? I messured the voltage with DC multimeter A=4.77V , C=2.96V, B=C=D=G=0. No signal palm dedected (with multimeter) while a photoshooting. How to sync for example leds with photoshoot?

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  • If you are building your own strobe, note that the central x-sync contact is all you need to use to trigger the strobe. If you hook up the other contacts, your camera might try to fire a series of pre-flashes that just complicate things and mess with any other slave strobes you might be using. – HamishKL Feb 14 '16 at 21:57
  • Dimitris, Were you able to create your own cable/cord to fire an external LED? If yes, how much voltage did the Hot Shoe generate? You think any off the shelf "off camera shoe cord" can be modified to goto my LED controller? Thanks – Hardik Singh Sep 12 '17 at 20:01
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The main signal that you want to know about is at the big contact in the middle, labeled X-Sync in your second image. To trigger the flash, the camera shorts this contact to ground (the sides of the hot shoe). It's not surprising that you didn't see this with a meter -- I believe the flash supplies the voltage, so with no flash connected there's no voltage to see. You could try setting the meter to continuity or resistance mode, but since flash duration is typically around 1/250s, the signal may be faster than what you can easily notice with a meter.

That much will let you trigger a flash in manual mode. To do more than just trigger (like using TTL metering or high speed sync), you'd need to know about the proprietary protocol that Nikon uses for controlling it's speedlights.

You can read more about basic triggering at Hot Shoe in Wikipedia, and there are some references on that page that may get you farther.

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  • Good news if it is closing the circuit. Yes I had tried the resistance mode but the speed was too fast, as you said. Thank you. – Jim Feb 13 '16 at 8:30
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    The sync voltage from the flash is A) a low DC voltage, typically about 6 volts today, but also B) protected with a high value series resistor, so that shorting it allows only a few milliamp current, and causes no damage. The flash trigger circuit senses this drop from 6V to zero when the shutter circuit shorts it to frame ground. – WayneF Feb 14 '16 at 19:33
  • @WayneF Re: "The sync voltage from the flash..." What typical flash? He's talking about making one himself, not buying one off the shelf. – Michael C Feb 15 '16 at 4:11
  • I omitted discussion of trigger voltages because the linked Wikipedia article discusses it, but it's nevertheless an important point that someone building a flash should be aware of the maximum trigger voltage that the camera they plan to use can tolerate. – Caleb Feb 15 '16 at 4:40
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To trigger a flash with a basic "fire" only command, the camera does not output any voltage at all. It just closes the circuit between the ground (G in you top photo) and the X-sync pin (D in your top photo). This allows voltage supplied by the flash to flow through the circuit back into the flash and fire the strobe.

Your camera can only handle so much voltage, though. And it can vary considerably by camera. Most Nikon DSLRs can handle up to 250 volts through the hot shoe. If your self built flash uses more voltage that you'll need to take some preventative measures to prevent frying your camera's internal electronics. Please read more in this answer.

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    Nikon dSLR hotshoes are good up to 250V. It's in the manual. – inkista Feb 13 '16 at 17:47
  • Sorry, I don't have a copy of "The" Nikon manual. Are you sure this is true of every single DSLR they've ever sold? – Michael C Feb 13 '16 at 23:28
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    The maximum sync voltage was not mentioned in the first Nikon D1 manuals, but from the D2 family on (2003), all Nikon DSLR specify 250V maximum sync voltage (in the "Use only Nikon flash accessories" section). Certainly all of the iTTL models do say 250V maximum. – WayneF Feb 14 '16 at 19:32

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