Circuit for releasing shutters of multiple cameras simultaneously WITHOUT external buttons?

Question

A EDIT: SONY camera release cable is usually designed to short two terminals (+5V EDIT: 3.17V, 0V) when the button is pressed, as shown in the following figure.

These two terminals also lose their voltage difference when a button on the camera body is pressed.

EDIT:

• When the camera is turned on and the switch is not pressed, a potential difference of 3.18 V is generated, and when the switch is pressed, a potential difference of 4.5 mV is generated.
• When the camera is turned off and the switch is not pressed, the potential difference is unstable, and when the switch is pressed, the potential difference is 0.0mV.

Therefore, I connected the terminals as follows so that when a button on one camera body is pressed, the shutters on all cameras are released. This actually works.

However, I thought that the potential difference between Shutter1 and Shutter2 might cause a current to flow in the opposite direction, which might adversely affect the camera with lower voltage. EDIT: In my situation comparing the two fully charged SONY α7, when two GNDs are shorted with crocodile clips, the potential difference is 0.2 mV and 0.2 µA flows when neither button is pressed, 136.9 µA when camera 1 button is pressed, and 138.6 µA when camera 2 button is pressed.

Thus I came up with the following circuit, will this work correctly? I am quite unsure as I am not familiar with electronic circuits.

The following solution is available as described here, but I would like to avoid this one because it requires an external button.

I modified the question and posted it on photo.stackexchange.com as well following this guideline.

https://photo.stackexchange.com/questions/135365/how-to-make-a-safe-circuit-that-releases-the-shutters-of-multiple-cameras-simult

Answer 1

The small voltage you are measuring when the shutter is triggered is a maintenance/status voltage; it tells the camera to keep the shutter latched in the open position for bulb mode, and that the shutter release is still held open/on for continuous mode. The same behaviors/voltages can be measured using an external switch. And the behaviors are the same for other cameras I have tested, although the voltages may differ a little (e.g. 2.7V/.15mV for Nikon D850).

For small camera arrays the status voltage is small enough to be inconsequential in operation and the diode is not necessary, the voltage will always take the path of least resistance to ground... i.e. reverse current is highly unlikely. In larger arrays the status voltages can accumulate and prevent reliable triggering of cameras on the circuit as they may not see the voltage drop to the required level (depending on circuit design). In that situation diodes and parallel ground connections are necessary. This is also explained in the solution provided here.

However, if you want to be certain you could place a single diode on the signal/shutter wire to make it a one way connection, with camera 1 being the lower voltage. This diagram is more accurate of the design; activating switch 1 will trigger camera 1, activating switch 2 will trigger both cameras (I don't think the ground interconnect is necessary).

Answer 2

You have no reason to suppose that every camera in the world uses 5V. Nor that “shutter” and “ground” are always of the same polarity.

Before you go any further, get yourself half a dozen cameras of each type that you use, in case you blow some of them up in your experiments.

If your cameras’ documentation specifically tells you the voltage and polarity used, does it also tell you what voltage on the input means “button pressed”? A mechanical switch can pull an input down to 0V. A conducting transistor never can. This may or may not make a difference. The camera manufacturer may know or may have forgotten; and may or may not tell you.

Given the expense of camera equipment and given the way your design is depending on guesses about how you think cameras ought to work - do reconsider the whole approach. A separate button which controls reed relays, a separate one for each camera, is guaranteed to work and guaranteed to be safe without relying on any undocumented features of cameras.