Solenoid actuator as a shutter release? Mythbusters style!

I've got a camera that doesn't allow any kind of remote shutter release, mechanical or electronic, and I'd like to rig one up for it. My idea is to use some kind of linear actuator Mythbusters style. I've seen them use these things to push all kinds of buttons and triggers.

I've been trying to research it but not finding much useful information, and I'm getting the feeling that if you can't already understand the complicated electronic diagrams and formulae, then you just shouldn't be trying to do this. I did manage to learn that apparently what I need is (I think anyway) called a solenoid actuator, which run on DC current. I've perhaps foolishly ordered a small one from eBay, that takes 12v DC, and thought it would be a simple matter to find a tutorial on attaching an old camera battery charger or something with a switch to use as a power supply, but not having any luck yet. 

Then it hit me - I should ask here on good old SMA - there are guys in here hooking up all kinds of stepper motors and Arduino cards - I hope at least somebody can direct me to some kind of resource for learning about how to do this stuff. Or maybe somebody knows of a better way to remotely activate a shutter mechanically? I mean I plan to literally build a camera holder with an arm above it where I'll attach some device to push down on the shutter button when I want it to. 

And before anybody mentions it - I have looked into using one of the old fashioned mechanical cable-style shutter releases. I used to have one of them for an old camera - not sure what happened to it but it seems like it stopped working, which according to Amazon comments they all do at some point - most pretty quickly. 

Ok, so any advice or links would be most appreciated! 

Edit- here's a picture and the info from the eBay page:

"10mm 10N Spring Load Push Pull Actuator Electromagnet Solenoid DC 12V"

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A little followup - I did run across one rather informative article that explained a few things in simple terms. I gather that solenoid actuators are either pull-type or push-type - meaning the electromagnet either pulls the shaft or pushes it, and there's a little spring providing counter tension in the other direction. And it sounds like the actuators heat up if you keep current running through them, so I think what I should get is a push-type, so the electromagnet is only activated while it's snapping a frame, and the spring is holding it open the rest of the time. Is that right? 

The one I ordered says it's a push-pull type (!?) Not sure if that's just dumb eBay typo stuff or if it's a real thing that I'm not aware of yet, but the whole listing was apparently written by someone with little to no English comprehension. It has a visible spring that seems to be pushing, so I believe it's probably a pull type (not what I think I need). I'd be willing to order a different one if I got the wrong kind - especially if it doesn't cost much more (around $12). 

Basically, my questions are -

1 what type of actuator do I need,

2 what can I use for a power supply and switch,

3 how do I hook it all up, and

4 where can I learn about this stuff? 

Oh, one more question-

5 is it dangerous to have an electromagnet close to my digital camera? I could mount the actuator a foot or 2 above if necessary with a long push arm. Or is that still too close?

I haven't done it myself, but I do have a degree in electrical engineering, so I might be able to help you make sense of things -- at least until someone with more practical experience than I have steps in and gives you better advice.  Do you have a data sheet or part number for the component you ordered?

You're probably looking at a circuit diagram that looks something like this. That's specifically for controlling the actuator from a microcontroller (e.g. Arduino).  The basic idea there is that the chip doesn't output sufficient power at a high enough voltage to actually trigger the actuator itself, so instead you wire the controller output to a transistor (the symbol on the diagram labeld with "base", "collector", and "emitter") which acts as a switch in a much higher powered circuit.  

The diode (on the diagram as an arrow with a line crossing the point) wired beside the solenoid coil (the loopy symbol) is a safety mechanism.  Diodes are electrical one-way streets; current can flow in the direction of the arrow, but is blocked in the other direction. When you trigger the solenoid, the coil actually stores a good amount of electrical power, and the diode gives it a safe path to discharge that power when the solenoid is disconnected.

If you're just looking to trigger it manually, though, you can use something much, much simpler; probably something like this would work.  Instead of a transistor, you can just use a button, or switch.  You'll still want to use the diode (called a "flyback diode" in this circuit) if you don't want sparks going off in your hand when you release the switch, and you'll definitely want a resistor in series with the coil.  When charged, the coil will offer virtually no electrical resistance itself, so the resistor (the zig-zag element) ensures that you don't end up with a short circuit.  (My memory's a little fuzzy here, but I assume that the circuit diagram for the Arduino controller doesn't use a resistor in series with the solenoid because the transistor itself regulated current flow?).  The strength of the resistor you'll want depends on the particular specs of the actuator you're using.

Does that make sense?

EDIT: Just saw your update -- hang on a sec.

Wow - I wasn't expecting a response so soon! Thanks Thomas! 

It makes some sense- I need to go over it with my tongue sticking out the corner of my mouth and scratching my head for a while and then it will probably make a lot more sense. I definitely want a simple hand trigger of some kind - this will be used to shoot behind the scenes stuff - you know, the animator at work, and I want the trigger to be discreet in one hand, possibly hidden behind something. Or maybe a foot switch? But I can work that stuff out myself - the point is I do want a simple trigger device. 

It sounds like I'll need to get a soldering iron and learn how to use it - something I've been meaning to do anyway for a long time. No problem there. Come to think of it I'm sure I've used one at some point, in school or something. Just need to brush up on the basics.

Ok, let me pore over your diagram and words a bit more deeply, hoping comprehension will dawn.. 

Edit - Ok, head-scratching and tongue-sticking-out done. I kind of understand the diagram, at least I can see now where the solenoid is, the Arduino card, and the transistor and the diode. It would help so much if there was also a picture of the physical thing, so I can compare the squiggly lines to actual objects and how they're attached. What is a heat sink for a transistor - is that some electronic component, or a piece of metal that vents off heat physically? 

And is the diode actually attached across both wires coming out of the solenoid? 

1) You're right; you'll want a push type (Push/Pull just means the shaft extends out the back when activated, so the one you found on e-bay probably works).  With a quick look on Jameco, though, I'd lean toward something like this one; I can't find a datasheet on the one you got on ebay, so it might work almost the same way, but I don't know.  One change to what I advised above, it has a coil resistance listed, so you shouldn't need an additional resistor in series.  Just that actuator, and a diode (this one should work)

2) For a power supply, something like this would probably work.  The actuator I linked only draws up to 100mA, so it should do fine.  The trick is getting the right jack for it... maybe this one?

3) To wire it all up, it'll be easiest if you solder stuff to breadboard, like this.  Use this schematic as a reference (ignoring the resistor). You'll want to connect the positive pin of the power jack to the positive input on the actuator, as well as to the striped end of the diode.  Then connect the negative pin out of the actuator to the other end of the diode, and connect those to one of the wires running to your button, however long you want that run to be.  Connect the return wire from the button to the negative end of the power jack, and you should be in business.

4) I went the expensive route, but this site has some good tutorials.

5) My guess would be that the actuator isn't going to mess with your camera. The magnetic field isn't going to be super strong any distance away from the coil itself, and I don't think DSLRs really use tech that a magnet would screw up (SD cards aren't magnetic storage).

Someone else with more practical experience can likely give better answers, but hopefully that helps!


Strider said:

Basically, my questions are -

1 what type of actuator do I need,

2 what can I use for a power supply and switch,

3 how do I hook it all up, and

4 where can I learn about this stuff? 

Oh, one more question-

5 is it dangerous to have an electromagnet close to my digital camera? I could mount the actuator a foot or 2 above if necessary with a long push arm. Or is that still too close?

I got so caught up in looking at your first diagram (Arduino) that I totally missed the second one!

Ok, I can see the switch - it's the thing that looks like an open door. I guess the circle with the + and - signs is the power supply? I can see the diode again, with the arrow running across both connections for the solenoid. But this time the solenoid has 2 sets of squiggly lines, a curly one with an L and a more jagged one with an R (left and right?) And I have no idea what the three horizontal lines are at the bottom.  Oh - ground I guess? 

This does seem much simpler. The more I think about it, a foot switch seems ideal. 

And thanks for linking to the Wiki page the diagram comes from - helps immensely! Still a lot of technical jargon that goes right over my head but the picture is getting much clearer now. Thank you again!! 

Just an interesting aside - do watts equal volts times amps? That's what it sounds like from one of the little blurbs. 

Yeah, it definitely helps to be able to look at an actual circuit as well as its schematic to get a handle on reading those diagrams -- the good news is, the outputs on the actuator are likely either labeled clearly as positive or negative, or they're actually interchangeable (the direction of current flow will affect the orientation of the magnetic field, but it'll have the same physical effect on the pin).  The diode has a clearly marked stripe indicating the orientation -- it conveniently corresponds to the bar on the diode symbol.

If you're just using a manual switch, you don't have to worry about heatsinks, but yeah -- that's just a thermal component designed to dissipate heat. A lot of the time it'll be a piece of aluminum with a bunch of fins lined up to increase the surface area.

And yes, the diode connects across the two terminals on the solenoid -- just make sure the striped end is pointing toward the positive power terminal, or else you'll let out the magical blue smoke that makes all electrical components work!

Strider said:

It would help so much if there was also a picture of the physical thing, so I can compare the squiggly lines to actual objects and how they're attached. What is a heat sink for a transistor - is that some electronic component, or a piece of metal that vents off heat physically? 

And is the diode actually attached across both wires coming out of the solenoid? 

Oh, yeah -- in that diagram, the L squiggle is the actual solenoid coil, and the R stands in for resistance.  In some cases, it's an actual resistor, but since the solenoid doesn't have an ideal inductor for a coil, it has internal resistance.  Just pretend like those two squiggles are both inside your actuator.  The rest of your interpretation of the diagram is correct.

And yes, watts = amps * volts (P=IV, where P is power, V is voltage, and I is current.  I have no recollection why)

Good luck! Let me know if you run into any more electrical questions.  Or, again, if someone who's actually wired something like this has other input, take their word over mine...


Strider said:

I got so caught up in looking at your first diagram (Arduino) that I totally missed the second one!

Ok, I can see the switch - it's the thing that looks like an open door. I guess the circle with the + and - signs is the power supply? I can see the diode again, with the arrow running across both connections for the solenoid. But this time the solenoid has 2 sets of squiggly lines, a curly one with an L and a more jagged one with an R (left and right?) And I have no idea what the three horizontal lines are at the bottom.  Oh - ground I guess? 

This does seem much simpler. The more I think about it, a foot switch seems ideal. 

And thanks for linking to the Wiki page the diagram comes from - helps immensely! Still a lot of technical jargon that goes right over my head but the picture is getting much clearer now. Thank you again!! 

Just an interesting aside - do watts equal volts times amps? That's what it sounds like from one of the little blurbs. 

Haha awesome! You've covered just about everything, and I feel like I understand it well enough to go soldering things together from Radio Shack! Of course, that's just enough knowledge to be dangerous.. 

Do you know if magnetism close to a digital camera will mess things up? Probably not something covered in electronics classes. The guy on my right shoulder says don't try it, but the other guy says "ah come on- what could go wrong?"  ;)

Maybe I'll go ahead and build it and try it next to an old crappy camera first.. 

Mounting the actuator right on the camera is probably fine, for a couple reasons --

  1. Magnetic fields fall off really fast (I'm sure you're familiar with the inverse square fall-off of light -- magnetic fields have an inverse cube fall-off, so even just a few inches away, you're not likely to see any magnetic effects from triggering the actuator)
  2. I don't think your DSLR actually has any components that would be really screwed up by a magnetic field -- even if you're shooting directly to an SD card rather than piping out to a framegrabber, the media DSLRs use isn't magnetic like hard drives are.

The only thing to be even possibly concerned about would be the fluctuating magnetic field (as you click the shutter) inducing current in nearby metal objects... but again, any distance away from the coil itself, you're very unlikely to see any sort of sizable effect.  I'd be surprised if you ran into any problems.

Wow, fantastic info!! Very encouraging. I was getting worried because I just bought a new SDHC card and it says to be extremely careful about static electricity, which can stop the camera from working until you discharge it. Must be different from magnetism, or like you said, the rapid falloff. Good to know, by the way!! 

 In related news - I have confirmation that if the spring is on the outside where you can see it, that's supposed to mean it's a push-type. The pull type has an internal spring. Weird, because it looks like the external spring must be pushing (and it's supposed to counter the electromagnet). Of course I've also read the exact opposite and several other possibilities as well.  Ah the internet - so much information, and so much of it wrong!! And when you go looking for confirmation all you find is people arguing like zealots. If only there was a simple way to tell the good from the bad. 

Day spent scouring Amazon, Wiki and other sources, and here are my tentative choices. Hopefully somebody can confirm if they'll work or not before I buy:

Diode:

Here's the alphabet soup listed under it:

"Rectifier - Standard RoHS: Product: Standard Recovery Rectifiers Configuration: Single Reverse Voltage: 50 V Forward Voltage Drop: 1.1 V Recovery Time: 2000 ns Forward Continuous Current: 3 A Max Surge Current: 125 A Reverse Current IR: 5 uA Mounting Style: Through Hole Package"

The reason I chose this particular one is because it says this on the Wiki page linked earlier in this thread:

"When the flyback diode is used to simply dissipate the inductive energy, as with a solenoid or motor, cheap 1N4001 and 1N5400 series diodes are used instead." - and this when you click the link included in that last sentence:

"The 1N5400 series is a similarly popular series for higher current applications, up to 3 A" (actually I have no idea how many amps the actuator is - I'm guessing 3 since most of them with similar power are).  Lots of guesswork here! 

Amazon link in case more info is needed.

Switch:

"Treadlite II Foot Switch, Electrical, Single Pedal, Momentary, SPD... (< that's a link)

I'm thinking a momentary switch is what I need, so it will only supply power while I hold it down, rather than continuously. It has a ground plug, which apparently is necessary. 

Power Supply:

12v 3a, should do the trick right? Amazon link. 3 prongs, will plug right into the back of the switch. I suppose I can cut off the plug and it probably has that weird thing inside where it's a single wire down the center surrounded by insulation and then a sort of mesh around it that carries current. Not sure how I can use that, but I'll experiment I guess. Every power supply I'm finding has that kind of connector on it. Or should I get a different kind of power supply, are there some made with just bare leads? Can't seem to find anything like that. 

DC jack adapter - that sounds like the ticket!  

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