Thanks a lot for your replies and feedback!
Your power supply requirements.
Doesn't have to be battery or computer power source, just a net adapter. Voltage would depend on what's needed to accomplish the task, I thought, but as I've seen 5V solenoids I don't know what would require me to go higher than that - but I'm sure there could be factors, please notify me if you can see any.
Depends on the physical force but normally over 1000 turns.
Yipes, having to wind 1000 turns would probably throw me off creating these myself.
Yes, in fact several [transistors]. You could use 74LS04 buffers and drive 20 shift registers with each one. There are six in a package.
Since it's just a logic signal where all 200 connections would be either high or low, why would I need shift registers for that? And what would happen if I tried to connect 200 enable pins directly to an Arduino pin? Would I get an over current condition or would the signal jus be too faint when spread out over 200 end points?
No wire, especially thin wire, has a significant resistance when you have 1000 turns.
Ok that makes sense! But consider this test I made:
I took an iron nail about 70mm long, put it in a thin plastic tube cut about the same length, then wound copper wire, about 1.2mm thick, just 20 turns around the tube from end to end. When I pulled the nail out a bit and connected the wires to a 1.5V battery, the nail was sucked back into the tube no problem. I could pull it out as far as two thirds of its length and it would still go back in in about a second. Not much force to spare I'm sure, but I don't need much more than that for my purposes. The wire and battery got hot quite fast if I kept them connected of course, but they would only energize for less than a second at a time with plenty of time to cool off between times.
So, what are the reasons a super simple coil like this wouldn't work? I mean I'm sure there are many but I want to understand it better.
The resistance in this case is clearly pretty much zero, so there would be a rush of current I guess, instantly cooking any transistors or other components involved? Couldn't they be protected in a smart way though? 200 relays, or can it be made easier, and cheaper? Or would I overheat my power source if I energized 20, 50 or 100 of these at once? How could that be prevented?
Lots of stupid questions there I'm sure, and you could of course refer me to chapter one of the book of electricity, but I learn these things much better when putting it into a context like this, so please bare with me.
Of course, I could wind the coils more than 20 turns and use thinner wire, I just used my test as an extreme example.
But if nothing else, this test gave me hope of being able to construct solenoids that run on as little as 1.5V!
I don't think you need 200 drivers. It doesn't sound as if you will need to power multiple solenoids solenoids simultaneously so you could multiplex then in a matrix. A 14x15 matrix would be enough to support 200 outputs.
Oh, interesting! I looked at a couple of examples of multiplexing for LED matrixes. But are you suggesting putting a motor driver before the multiplexing bit and then multiplex that driving current coming out of it? Seems like it would require some very sturdy shift registers for sourcing/sinking current? Also, do you think alternating between energizing all these different solenoids very fast would energize them enough to pull the plungers?
Have you considered a simple lever @ 1/4 amp/solenoid is 50A total
Yeah, that's a lot of current. I guess what I'm hoping for here is to find a way to design the solenoids so they don't require so much current, since they don't need to be very strong.
The lever concept and semaphores (as hinged flags) might simplify what appears to be a mechanically challenging task.
Could you elaborate, please?
What about using servos ? They could be a little more expensive, but they are in the same price range. 200 servos at 5V with a computer power supply could be done.
I guess it's one way to go, I just liked the idea of making the actuators myself if the low requirements made it possible and practical. But using servos or even DC motors is not completely out of the question if it would offer a great advantage.
The Arduino Mega can control up to 48 servos. So a few Arduino Megas is all you need.
Oh, that's all? :-) Seems like a hell of a lot of hardware for a thing like this, doesn't it?
The metal moving core in a solenoid is not a magnet, so reversing the polarity won't change anything. The metal core will move in the same direction.
Now, THAT'S good input, thanks for pointing that out. Makes perfect sense, should've seen it myself. Guess I just misunderstood what role the permanent magnet played in a latching solenoid.
So, as a consequence of that, I'm now thinking more in the lines of two separate coils per solenoid, wound over slightly different segments of the tube but overlapping for the most part. Each coil would pull the plunger into the centre of that coil when energized, right? So I'd use one for pull and one for push.
And I would not need any IC's for switching polarity, but instead I would need twice as many transistors or something for switching the current, unless there some better way. Maybe there are three-way transistors, that can either connect a circuit this way, that way, or disconnect it. I'll have to do a little more research there.
And, as several of you have suggested, I'll do some tests and measurements before buying 200 of anything here. Good advice.
Thank you again for all your good input, and keep it coming!