Detect-if-Connected circuit for DSLR -low voltage, low current.

Thread Starter

TechRat

Joined Oct 20, 2010
5
Hello,

I have a DSLR camera which will have a long, wired remote trigger controlled by a microcontroller (I'm using an STM32 Nucleo).
My goal is to:
A. Detect that the remote trigger between the camera and MCU is plugged in, and illuminate an LED.
B. Have the MCU trigger the shutter (take a photo).
It must be a wired solution. I know there are wireless options, but they are not suitable for the project.

The camera trigger port seems to have about 1.8V and 0.2mA max.

Currently, I have part B working - I'm using an optoisolator (4N27) where the IR led is controlled by the MCU, and the transistor acts as a switch to shutter the camera and I take a photo.
Since the camera is using a battery, and my MCU will have it's own source - I believe I need the isolation so the grounds are totally seperate.

I'm having trouble with part A - The camera trigger isn't going to power an led for the optoisolator, so I think I need to sense the voltage present and translate that into an output the MCU can read and then the MCU can drive an indicator led that the trigger is connected between the camera and the MCU.
I've found some isolated amplifiers like AMC1302 - but I don't understand how to implement the 'high side' and 'low side' or 'floating' power supplies. I only have my MCU source, and the camera trigger signal.
I'm actively researching this, but before I went too far down a rabbit hole I wanted to solicit some experience as to whether this a solution I can use, or is there something better/more obvious?
Thanks!
 

Reloadron

Joined Jan 15, 2015
5,604
I use a wireless IR remote with my camera. I have no idea what you have as to pin out. Using my Canon EOS 7D mine looks like this:
Camera Remote.png

Schematic wise this is what the wired remote looks like:
Camera Remote 1.png

The camera has a pair of internal pull up resistors (50K). If I measure drom either the shutter pin or focus pin to Ground I see just about 3.3 volts which is pretty common. To detect if a remote shutter release is connected I could likely take advantage of the 3.3 volt presence keeping in mind there is 50K Ohm pull up resistors in there. While I am not familiar with your uC it should detect a logic high if connected to your shutter release pin so you may want to try that approach?

Less a good schematic of what you have it's all guessing.

I see no need to isolate grounds? I would make all grounds common (bonded).

Keep in mind that most uC like to see a source impedance of around 10K so consider that. Not sure how yours as an Analog In or Digital In will like that or what your camera source impedance is?

Ron
 
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Thread Starter

TechRat

Joined Oct 20, 2010
5
Thank you for that!

My remote trigger is a male aux connector, two wire.
I've attached the schematics of what I see from the camera side, and from the remote trigger I pulled apart as well as what I've done to drive the trigger. It's not much - I see about 1.8V, 0.2mA across the two trigger wires and I measure 12k-ohms across them when everything's off.
I don't need (or want) the autofocus so I'm just imitating the shutter. Interestingly, the resistances to trigger the shutter are quite specific. Simply shorting the two trigger wires together does not trigger the shutter.

I'm unsure of what the camera-side is doing. I'm not sure I'm really comfortable just bonding the "grounds" together? It's an expensive camera, and not mine so I'd rather take a safe route of detecting some voltage or current on the trigger and reporting it to the MCU?
 

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Reloadron

Joined Jan 15, 2015
5,604
Interesting take on how they do it. I assume the Opto isolator is used because you want isolation. Years ago before I bought an IR Remote all I did was shorted the Shutter Pin to Ground using a common 2N3904 transistor. Had I been using a uC I likely would have taken the opto route. Are you trying to bias the opto coupler with R5? Anyway if the camera provides even 1.8 volts and your uC has an Analog In channel available I would take advantage of that to know when a connection is made.

Ron
 
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