Hello everyone. This is my first post and my first Arduino project. I have a good understanding of electronics and principles but only at a hobby level and I don't play with electronics at this level often.
I am building a water drop photo controller. It utilises an Arduino with a air/water actuator and the 4N25 is used to trigger the camera shutter, which is just shorting 2 pins from the camera's remote jack.
Everything works fine except the camera trigger. I believe it is due to the resistance I am seeing on pins 4 and 5 (E and C) of the 4N25. If I short the camera's remote pins directly the camera shutter works fine.
I have hopefully attached a picture of the circuit. I nabbed it from the guide I was following. The break down is as follows:
Blue - Ground
Yellow - Pin 9 of Arduino (4.76V)
Purple - Camera GND
Green - Camera shutter
The resister in the image is not the one I have used. The value I calculated is 326 Ohms and am using a 330 Ohm resister. With that I am seeing 134 Ohms at pins 4 and 5. I expected this to be just a few Ohms, if any. I tried a lower resister at 300 Ohms but it blows out to 3K (which I understand) but a bigger resister at 430 Ohms increases to 168 Ohms. I seem to have hit the right resister at 330 Ohms but don't understand why I have resistance across pins 4 and 5. I have searched and played for 4 hours using multiple 4N25's and have also used 4N35's with no difference.
I would very much appreciate some insight into how I can get this resistance down enough to allow the camera trigger to function.
Good start but you need to do some more research. The 4Nxx devices are transistor output, not resesitive. For that you need a MOSFET Output Optocouplers. You will need to build additional circuitry to make this work. The camera trigger voltage, current, etc needs to be known to properly design the interface. Probably the best for you is to use a relay output, then it is not polarity sensitive. The delay caused by the relay will be small. This response is to help you get started in solving your problem, not solve it for you.
Good Luck & Have Fun!
Gil
Measuring the resistance of a transistor is a meaningless thing. It tells you nothing and has no relevance. Forget it and move on.
You want to measure voltages. Measure the voltage on camera’s trigger output and then measure it again with the input LED activated with a constant voltage input.
Sorry but that “diagram” conveys zero meaning, it just shows wires going into a chip and I am not even sure it does that.
It is about as useful as gilhultz advice which is too good for the bin.
If you are just connecting the pin to Camera ground, I'd go with a N-channel MOSFET with low Rds to act more like a relay that connects the pin to Gnd.
Polarity matters.
Are you sure the positive coming from the camera is connected to the collector (middle pin) of the opto?
Measure the voltage on pin 4,5 of the opto (transistor) when it's not being triggered.
Leo..
Thank you all so very much for taking the time to reply and offer your assistance. My apologies for the late reply.
Wawa you were on the money! I saw it was a transister so may times but it didn't click that I had the polarity backwards. I didn't have access to a camera so made a quick LED test and sure enough it didn't light up at first but once the polarity was reversed it did. I checked with the camera yesterday and rejoiced in the glorious sound of clickclick.
Again, a huge thank you to everyone who took time to respond to me. I greatly appreciate it and have learnt a great deal from this process.
Another little thing to be aware of - the 4N25 has a current transfer ratio (worst case) of 20%. This means if
the output circuit wants 10mA, you'd need 50mA on the emitter side to guarantee that, which is rather close to
the absolute maximum rating of 60mA.
For switching more current there are other opto-devices, such as opto-thyristors and triacs, although they don't self-cancel until the output current drops to near zero.
