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12-15-2015, 09:41 AM   #1
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Remote Shutter voltage

What is the voltage output of the shutter release cable port on a K-50?

I'm working on two different projects with the same common question. The remote shutter release cable is just a switch that allows the present voltage to complete the circuit to fire the camera. I've read that it's an extension of the native shutter release button but can't confirm. My projects require a programmed microcontroller which basically means I will use a transistor as a switch. I'm pretty new to transistors so if I can use one without adding any voltage to the camera circuitry please let me know how. I have a theory but finding info on the net is like drinking from a fire hose and I've yet to find my simple answer.

If I get these properly working I might post details on the projects.

Thanks!

12-15-2015, 09:48 AM   #2
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I'm not an expert in Electronics, but I think I can help.
Yes you can.
A transistor is an electronic switch, the microcontroller can control it with the base (middle leg)? without adding any voltage to the camera.
I am halfway through doing a similar project with an old RF toy control.

PS What microcontroller are you using?
12-15-2015, 09:59 AM   #3
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My only worry was that the base voltage would be added. I know it must be added to the emitter because that is ground and otherwise it would be an open circuit. That said, the drop may be enough to not hurt anything. My theory is that I can keep my camera on collector/ emmiter and the completely different control voltage hooked to base/ emmiter. The only thing that makes my usage questionable is using two different circuits and voltages instead of using a common ground.

I am planning to use an AtTiny85 to control a servo and shutter release. It turns just a tiny amount, triggers the shutter, waits 15 seconds, repeats. I have modified the servo to unlimited rotation and never return 'home'. When it receives a command it follows it but stays put when the command stops. No indexing. The plan is to use this for night lapse photography with very slow rotation to add another dimension. It pauses motion while the camera fires in order to keep as still as possible.
12-15-2015, 10:05 AM   #4
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You can messure the voltage by a multimeter, but I think a normal bipolar transistor will be in the voltage range definitly.
It should work for pentax too:
Time-lapse shutter release based on Arduino | Axotron Blog
3.3V or 5V should open the transistor, so don't worry.
You can't damage the camera by this circuit.

12-15-2015, 10:12 AM   #5
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I am curious about this myself, but haven't had time to dig into it. You should be able to plug in a connector to the remote connector with open leads and measure voltage across it.

Assuming the voltage is at or below the battery voltage there are a ton of different transistors that would work and some other devices like an opto-isolator. I don't have a K-50, but I am hoping that the Pentax cameras are consistent on how this connection works??
12-15-2015, 10:15 AM   #6
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QuoteOriginally posted by KC0PET Quote
but I am hoping that the Pentax cameras are consistent on how this connection works??
I think so.
12-15-2015, 10:16 AM   #7
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I assumed this was safe but she's my first DSLR and has been so good to me in our short time together. I expect to be a lifelong Pentaxian. I had to sell another camera to buy this and money is quite tight so if I blow this up I'm without a camera for a very long time.

---------- Post added 12-15-15 at 11:18 AM ----------

And I do plan to measure it when I get home but though maybe someone might have the number handy. I'm using an online simulation program to write the code and test the components. Everything is done and working but I just need to confirm it is safe on my particular use. Some of my projects make it hard to focus at work....

12-15-2015, 11:33 AM   #8
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You basically have two problems, voltage, and current. Your voltage should be between 3.3 V and 5 V, So that should not be a big problem. current should be less than 25 mA, again not a problem. Some processors will not take more than 3.3 V, And in some cases less than 1.5V. so It would make sense for Pentax to buffer this input to allow for this. but this is a unknown. More than likely they used a pull up resistor to set the input pin to high, and allow the input to be pulled low. This allows minimum current to be used without endangering the processor. Having said that, careful testing should be made to make sure this is the case.

Regardless of what voltage is used, it is recommended that you use an optical coupler to couple the camera to the microcontroller. This allows you to switch the current without having any voltage, positive or negative going between the microcontroller and the camera. A MOSFET can also be used. A MOSFET is a voltage controlled transistor. When voltage is present at the gate, the transistor is turned on, allowing voltage flow between drain +, and the source -. However no voltage actually flows from the gate to either drain or source. The power is still isolated. Unlike the standard NPN transistor, which is a current control device. You have to have current flow between the base and the emitter for current to flow from the collector to the emitter. This negates any isolation possibilities. A MOSFET can also have less resistance to the current flow.

either a MOSFET or a optical coupler should work fine.
12-15-2015, 12:36 PM   #9
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Wouldn't the mosfet have the same situation as the npn? The gate or base, respectively, can't just get a signal and open, they need to ground somewhere to complete the circuit in order to provide continuity.

I've attached a screen shot of my breadboard. Ignore the servo. As you can see, pin 6 outputs 721mv after the 1k resistor. This is the .7 needed to trigger the NPN to then allow my 1.5V to flow to the LED. The LED is only there to simulate my 'second circuit' which is in this case the camera. All I need is continuity. I've never messed with MOSFETs but can't get it to work. The NPN seems to be working wonderfully

What am I missing here?
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12-15-2015, 12:38 PM   #10
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Arghh, I can't think right now. Sorry I can't help. You might have better luck if you asked in an electronics forum instead.
12-15-2015, 12:52 PM   #11
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Which type of MOSFET are you using?
12-15-2015, 01:12 PM   #12
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It's an NMOS. I suspect the problem is with me hooking it up incorrectly. I certainly would have posted in an electronics forum had I foreseen this mess haha. I just wanted a K-50 shutter voltage. I have the NPN working perfectly and see no reason to switch to a MOSFET. I still get voltage on the simulated camera circuit when there is no power to the mosfet. I've yet to figure out how to use them but I will press on.
12-15-2015, 02:03 PM   #13
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on an MOSFET, the gate is Insulated from the source and drain. There should not be any direct connection between the gate and any other pen. If there is the MOSFET is bad. it is the "field affect" that causes the transistor to conduct current, The existence of a voltage potential at the gate, produces a magnetic field which in turn, turns the transistor on. Not an actual connection between the gate and any other pin. Note: in most cases, once this field-effect is initiated, disconnecting the Voltage from the gate will not turn off the transistor. The voltage must be sent to ground through a resistor. Commonly a 1K resistor. But it can be most any value that does not drop the biased voltage below the Saturation voltage of the MOSFET. also note: the MOSFET should be a Advanced logic level MOSFET. in other words the gate saturation voltage should be no greater than 5V. there will also be a threshold voltage at the gate to turn on the field-effect, normally about 1.5V. check the datasheet.
12-19-2015, 05:59 PM   #14
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I would play it safe and use an opto-isolator.
12-19-2015, 06:15 PM   #15
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QuoteOriginally posted by shortphaselabs Quote
And I do plan to measure it when I get home but though maybe someone might have the number handy.
Just measured it on my K7. My fingers holding the probes dropped the voltage down from 3.288 volts.
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