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I am attempting a circuit design that involves connecting to a DLSR camera PC port. Newer digital cameras deliver very small amounts of current (mA) to their PC port during shutter release. This very small current sets off the flash to any connected camera flash. My circuit will connect a very old flash to this new digital camera. Old flashes (Flash bulb flashes) are triggered by higher amperage amounts. These higher amounts would fry the controller board on the digital camera. Hence a circuit in between.

I need to understand exactly how many mA are sent to this port, when the camera’s shutter is triggered, but because the duration of the current is in the milli-second timeframe, I do not know how to use my multi-meter to capture a current this short in duration.

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    \$\begingroup\$ The PC poet does not supply any current or voltage when the shutter is pressed. All it does is short the two contacts together momentarily. The flash supplies a voltage on the center pin and when the camera shorts that to ground the flash fires. The problem with older flashes is that they provide a very high voltage (200V or more sometimes) and the switching circuit on modern cameras (a transistor instead of a physical switch) cannot handle the voltage. \$\endgroup\$ – Frosty Oct 12 '17 at 0:36
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    \$\begingroup\$ The general approach to measuring a current of a very short duration would be to use a shunt resistor and an oscilloscope. \$\endgroup\$ – Frosty Oct 12 '17 at 0:43
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    \$\begingroup\$ you can use an optoisolator circuit/ic to protect your fancy camera \$\endgroup\$ – dandavis Oct 12 '17 at 6:52
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You are mistaken — electrically, the PC sync port functions identically to a hot shoe connection: the camera simply provides a contact closure to ground. In modern cameras, it's actually an open-drain or open-collector output. Any voltage or current is supplied by the flash unit.

But to answer your actual question about the multimeter, if it doesn't have a peak-hold feature built into it already, it isn't something that you can easily add. Get a different meter.

Any further questions on this topic should probably be directed to Photography.SE.

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  • \$\begingroup\$ Understand both responses. Thanks! Just for clarification however, old electronic flashes or strobes have excessive voltage. Flash bulb flashes however, for the most part do NOT have high voltage. Rather they have high amperage. That is why I am unable to use one of the existing solutions available for old camera flashes (Wein Safe Sync, etc).......... \$\endgroup\$ – B. Varner Oct 12 '17 at 2:48

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