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I've got an idea for a little project that uses the hot-shoe on top of the camera - I'm aware that the standard centre pin / foot connection is a universal thing but it would be useful if I could take power from the camera too.

My specific camera is a Pentax K5 which has a couple of extra contacts on the shoe, I don't know if this is Pentax-specific or a more universal standard that came along.

Does anyone have any information on the electrical side of the hot shoe, is there any sort of standard or does each manufacturer do their own thing? Any pinouts, voltages etc. would be greatly appreciated.

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    All the "hot shoe plus" connectors I'm aware of are to let the camera control the flash; as such, there's no sensible reason to power those connections from the camera battery, vs. from the flash battery.
    – Zeiss Ikon
    Mar 23 at 14:04
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    And the first answer talks about camera-powered mini-flash units and other accessories up there. Okay, now we know why I prefer to stick with cameras old enough to be fully mechanical.
    – Zeiss Ikon
    Mar 23 at 14:35
  • @ZeissIkon You have my sympathy. I am essentially refusing to use flashes with camera-specific functionality beyond what the SCA3000 system can provide, and by now am mostly back to ancient autothyristor flashes working just from center contact and packing a punch. Not willing to buy one flash per camera model.
    – user98068
    Mar 23 at 15:13
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The two hotshoe designs with power supply contacts for small accessory flashes are the newer-version micro four-thirds (Panasonic/Olympus) and Fuji hotshoes. The power contact on both of these is brass-colored.

images of old/new versions of the Fuji and MFT hotshoes

AFAIK, none of the other camera brand hotshoes have a similar contact. The non-sync contacts are primarily for electronic communication for features like TTL and HSS.

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  • I assume TTL is "through the lens". Considering the OP is seeking to power electronics, it might be confused with the "TTL logic" voltage level, which is probably not what you're intending. =)
    – scottbb
    Mar 24 at 5:59
  • @scottbb, since I say I'm talking about flash features, I think the assumption that I'm talking about the TTL auto-power setting flash feature, and not a flavor of semiconductor tech is reasonable. :D
    – inkista
    Mar 24 at 8:33
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There are some cameras coming with mini flashes without a power source of their own (such as the Panasonic DMC-LX100): naturally they need to provide power on their extended flash ports. In a similar vein, there are powered accessories like A/D converters with XLR microphone inputs occupying an extended flash port: again this requires some power to be available on the connectors.

The problem is that each manufacturer has their own extensions (and often changing across the model line) to the center pin standard, and they are all proprietary and different. The MFT consortium has united on a standard for their respective models (but I don't think it is an open/published standard), but other than that, it's essentially every manufacturer for themselves.

Somewhat painful for flash manufacturers.

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The manufacturer specific additions to the standard hotshoe are mostly for data transfer between camera and accessory.

The common flash connections, ISO 518 hotshots and PC ports, are simple switches that close the circuit between their two terminals. If there’s something connected then current can flow.

Electrically the design requires external power.

An accessory design requiring camera power is probably not sound in the sense that it is almost certainly simpler to add a power source to the accessory than to figure out how to draw it from the camera. It also makes the accessory suitable for more cameras.

If you only need a little power a photocell might be an option. If you need a lot of power, then the camera was a dubious power source anyway.

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