View Full Version : Electronic button pusher?

03-20-2006, 11:57 PM
Sort of along the lines of Nicolai's thread, but simpler: What kind of device would push a shutter button down? The original thought for this was to wire some sort of electronic cable release for the Holga. I can imagine how a small motor inside the Holga would suffice, but I'm still curious about what component moves in and out, in just one direction.

03-21-2006, 12:40 AM
A solenoid. Some push, some pull, some do both. Check http://www.jameco.com for examples (search on solenoid).

03-21-2006, 06:47 PM
If you're going to hold it for any length of time, however, you need to reduce the voltage to the solenoid to avoid damage to the coil from overheating. I don't recall the amount needed; some solenoids will actually give "pull-in" and "hold-in" current requirements, but it's pretty uncommon.

Also, a solenoid with any significant power will tend to be big, heavy, and need a biggish battery.

Simpler would be a small geared motor with a cam on it; you could even put in a microswitch to operate off the opposite side of the cam so it *stops* when the button is fully depressed, until you start it with a second switch (that bypasses the cutoff switch). Or you could use the bypass directly for a "momentary" actuation, of course. The motor and some of the gears out of a P&S motor drive would be just about right for this, I'd think...

03-22-2006, 12:33 PM
Electric shutter drive technique is typically apply 4 x rated voltage for about 5-10 electrical time constants to open faster than normal, then reduce to 1/2 the rated voltage to hold open.

Sounds complicated, but once someone figures out the math for a given solenoid, it's just applying the voltage thru an RC network carefully selected. Somewhere, in that big set of boxes o projects I have a schematic for an Ilex controller that I figured this out for, along with measuring the L & R of the solenoid. Somewhere I have data for Ilex (synchro) electronic shutters too...found the company that made their solenoids, got the guy to talk and between the time he said hello and eventually realizing he talked too much, I got some good info :O).

On the other hand, if you aren't trying to achieve the maximum speed capability, the rated voltage should be fine unless it has a duty cycle limit.

I will find this info someday in the next couple months...maneuverability in the basement has been reduced to near zero.

Pull-in voltage and holding current comes to mind.

03-22-2006, 12:42 PM
In the spirit of avoiding simplicity, which might inhibit the development of variations on a theme, consider the following 'overkill' device & circuit. Tnen we can simplify.

It's got power, levitation, AND self-wound coils, so it has the raw materials to move a shutter or maybe even an auto-focus view camera!


03-23-2006, 04:41 PM
The few electric shutters I've seen don't actually lock the solenoid to hold the shutter open. Instead they either have two solenoids, one to open the shutter and one to close it, or they have some sort of over-center arrangement where one push (or pull) from the solenoid opens the shutter, and the next one closes it.

An example of the former is here: http://www.surplusshed.com/pages/item/m2410.html

Look at the two views to see the solenoids on the front and back.

As long as bulb exposures aren't too long, a simple button-pusher might be fine. This is, after all, for a Holga. Make it too fancy and I'm sure the camera will refuse to work with it.

Jim Jones
03-23-2006, 06:55 PM
The shutter and solenoid from an old press camera might serve as an electrically controled external shutter. These shouldn't be too expensive if the lens is bad or missing.

03-30-2006, 10:32 PM
Wow! Thanks for all the responses. I've been away from the internet for a week (what a weird experience) and this is good info all to return to.

04-20-2006, 04:53 AM
My idea to make a simple electrical shutter is to use a solenoid of an old hard drive. I've just tried it with a 1,5 volt size AA baterrie. It move very fast. I've soldered 2 wires to the solenoid as you can see on the picture. We can easyly imagine a sort of adjustable timer in order to make the exposure.

Attached files http://f295.f295.org/uploads/hdd_7028.jpg (http://f295.f295.org/uploads/hdd_7028.jpg)

04-20-2006, 05:00 AM
Another picture, the moving part is the on the right side of the picture.

Attached files http://f295.f295.org/uploads/hdd2_2608.jpg (http://f295.f295.org/uploads/hdd2_2608.jpg)

04-20-2006, 04:18 PM

that's actually called a voice coil motor.

There is a scientific paper on the web that used a half bridge or H-bridge (I don't remember) motor drive circuit to precisely position the arm in the center then move to either stop. It was used for a laser shutter. They discussed speed & loads it could move.

I was envisioning this...and actually you made it more elegantly simple...no motor drive!

You might want to see if you can add resistance to minimize current draw and still operate quickly enough. You don't want to wear the battery out too soon, and you don't want to over heat the coil.

I had two other ideas...extend the length of the arm to get more 'distance', and the 2nd idea was to use the short throw of the mechanism to move a 2nd lever arm to get longer throw.

Good work.

04-21-2006, 05:37 PM
OK, Toniox.

Now you have me motivated to find one I took apart (or do another).

I want to figure out some electrical stuff for this, and maybe contribute some thought.

04-25-2006, 05:06 PM
The hard drives I took apart yesterday appear to need the center mounting post to keep the bearing centered,

I found an article that discused using these for robotic mechanisms...they really abused them with fairly high current...more when I have results.

04-28-2006, 02:08 PM
You folks are making this way simpler than it has to be.

I recently acquired a 6-channel radio control set for a song. In the spirit of overly complicated, I can see one channel for the shutter, one for controlling the film spools, and two more for the 2-axis motorized pan/tilt head.

That leaves 2 channels left. You could mount the camera on an off-road RC car chassis. You sit in your automobile, and drive the beast out to the "scenic" location. Using wireless video feed, you can preview and compose the shot, then advance the film and move on. No more back breaking treks with LF gear, yessirree.

If NASA or the European Space Agency can do it, why not us? I say lets get on the bandwagon NOW! Where's Sarge when you need him?

04-28-2006, 04:12 PM


Steve Smith
10-12-2006, 03:23 AM
The simple way to drive a solenoid, if you want to keep it on for any length of time, is to power it through a resistor with a fairly large value electrolytic capacitor accros it.

The resistor is selected to supply just over the minimum current required to keep the solenoid active.
On switching on, the capacitor is discharged and effectively has a low resistance. The only way it can charge up is to draw current through the solenoid coil which initially would be quite high - hopefully high enough to operate the solenoid. As the capacitor charges, the current it draws drops to zero as it's voltage reaches that of the power supply. At which time the resistor takes over and supplies enough current to keep the solenoid on.

With the righht selection of resistor and capacitor values, you should be able to get enough initial current to operate the solenoid and then a low enough holding current to give a decent battery life.