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DIY electronic shutter release weirdness

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silverfoxxx

New Member
I built an electronic camera shutter release using a microcontroller and an optocoupler and a socket a stereo phono jack to accept the shutter release cable. Pretty simple stuff. To fire the shutter, the tip and ring of the jack have to be shorted to the sleeve of the jack. And that is what the optocoupler ostensibly does. But I am having a problem that I don't quite understand. The micro always does its thing as expected and the optocoupler does its. But the camera mostly isn't responding as I thought it would. It doesn't fire the shutter UNLESS I have my DMM leads across the socket pins to measure the resistance drop while the optocoupler is triggered. In that case it ALWAYS works. I am guessing that there is some internal resistance in the DMM that is resulting in my circuit working, but I don't know why that matters or how large a resistor I should add to my circuit to simulate the DMM. Any thoughts?
 

audioguru

Well-Known Member
Most Helpful Member
When your DMM is measuring resistance then it has a voltage and small current across its probes. It is simply a high value resistor when measuring voltage and is a very low value resistor when measuring current.
I do not know why the camera shutter circuit needs the small voltage and current.
 

Tony Stewart

Well-Known Member
Most Helpful Member
measure the camera Open circuit voltage. If there is none that's a problem. If it is the wrong polarity , that's a problem.

The DMM is providing a certain polarity +V on red + in.

I believe your opto polarity is reversed for the camera detector and the DMM in the opposite polarity provides the correct bias.

Try a PNP open collector instead of NPN by cascading a PNP to the output with Rb in series
 

AnalogKid

Well-Known Member
Most Helpful Member
Your guess is correct, probably. Post a schematic or sketch for a more informed response.

ak
 

tomizett

Active Member
I think Tony may have it - remember that an optocoupler will only conduct in one direction, unlike a relay.
Possibly a Schottkey rectifier bridge before the opto would make the circuit independent of polarity (or perhaps it will just introduce too much voltage drop and stop it ever working).
 

silverfoxxx

New Member
measure the camera Open circuit voltage. If there is none that's a problem. If it is the wrong polarity , that's a problem.

The DMM is providing a certain polarity +V on red + in.

I believe your opto polarity is reversed for the camera detector and the DMM in the opposite polarity provides the correct bias.

Try a PNP open collector instead of NPN by cascading a PNP to the output with Rb in series

Yes, the polarity was wrong. I used the polarity that I saw on another camera control circuit but it was apparently wrong. I didn't try changing it for the longest time. I was out of internet access for the past day so I didn't see your comments until now. So although I eventually figured it out on my own, thank you for your help.

BTW, the weirdness was even weirder than I first thought. My DMM has resistance ranges of 200, 2K, 20K, 200K, 2M. Of all those only measuring in the 20K range caused the circuit to work as it was intended to.
 

Tony Stewart

Well-Known Member
Most Helpful Member
not weird if you understand that each lower range is actually a higher constant current source up to ~ 1mA for each decade.
 

silverfoxxx

New Member
I discovered the root cause of the problem. The schematic symbol for the package has the emitter and collector reversed. I hooked it up right according to the package in the library My error was not checking the symbol against the datasheet. Which I will be more careful to do in the future.
 
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