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Author: Subject: Any interest in a magnetic stirrer that can cycle speed/direction automatically?
Melgar
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[*] posted on 28-9-2017 at 22:43
Any interest in a magnetic stirrer that can cycle speed/direction automatically?


We've probably all experienced a magnetic stirrer that went a bit too fast, eventually clanking around the vessel instead of stirring like it was supposed to. To make it stop, of course, you have to turn the stirring off, or at least down very low. Then the magnets align, and you can turn the speed up again. There's also an issue where, over time, there will be "sand dunes" of a solid reagent that get stuck to the bottom, where they form because of the consistent fluid flow over them. To solve both problems, I was thinking that perhaps a stirrer could stop and change directions every five minutes or so. It would go the same speed as it was set to, just the opposite direction, and adjusting the speed would reset the timer on the cycle so that it would never change directions in the middle of adjusting the speed. I was about to build the thing finally, but figured I'd ask here to see if there were any considerations I should be sure to keep in mind.

The motor I have is actually from an old videodisk player, and was made by Sony. It's actually a perfect DC stirrer motor, I think. Very smooth motion at all times.




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[*] posted on 29-9-2017 at 01:50


maybe just changing the size and/or shape of the stirbar would be easier ?

e.g.
http://www.ebay.co.uk/itm/PTFE-Magnetic-Stir-Bars-High-Magne...
http://www.ebay.co.uk/itm/PTFE-Magnetic-Stirrer-Gear-Type-Oc...
http://www.ebay.co.uk/itm/Bel-Art-Products-371520000-Spinbar...




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[*] posted on 29-9-2017 at 01:51


You could always make a controller such as that. With a motor controller, RTC, and an ardiuno you could construct such a device.



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Melgar
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[*] posted on 29-9-2017 at 03:15


Quote: Originally posted by VSEPR_VOID  
You could always make a controller such as that. With a motor controller, RTC, and an ardiuno you could construct such a device.

That was actually the plan. The stirrer on my hotplate is broken, and rather than just use it without a stirrer, I figured I'd replace it with a custom-made one. I have an H-bridge motor controller, (to switch polarity on the motor) and since the motor only draws about 100-200 mA, the controller should work fine without any power-boosting circuitry. I mounted the original permanent magnet onto the new motor already, now I just need to build a mount to hold the motor in place inside the hotplate, hook up the stirrer potentiometer, then write the arduino code. I took apart an old 12V 500 mA AC adapter, and that circuitry should be able to provide the necessary DC power to the system, and can be hooked up internally. But if I'm going to be putting an Arduino in there, I feel like I should add more functionality too, while I'm at it. Of course, I'd then need to add more controls somehow, or hook up a bluetooth module and use my phone to control and write control software for my phone or something... but I should probably just focus on the stirring for now.




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[*] posted on 29-9-2017 at 09:52


For those who prefer something that doesn't involve Arduino or programming for that matter, you can build the entire controller circuit for $5-15 USD:
You can get the "relay" there (a double-pole double-throw) for less than $5 (usually), and control the relay using a 50% duty-cycle 555 timer circuit, which costs MAX $4. Probably cheaper. Personally, I'd prefer Arduino though.

EDIT: God dammit, images are such a pain.

DPDT-relay.png - 16kB


[Edited on 29-9-2017 by CRUSTY]




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[*] posted on 29-9-2017 at 13:37


Quote: Originally posted by Melgar  
Quote: Originally posted by VSEPR_VOID  
You could always make a controller such as that. With a motor controller, RTC, and an ardiuno you could construct such a device.

That was actually the plan. The stirrer on my hotplate is broken, and rather than just use it without a stirrer, I figured I'd replace it with a custom-made one. I have an H-bridge motor controller, (to switch polarity on the motor) and since the motor only draws about 100-200 mA, the controller should work fine without any power-boosting circuitry. I mounted the original permanent magnet onto the new motor already, now I just need to build a mount to hold the motor in place inside the hotplate, hook up the stirrer potentiometer, then write the arduino code. I took apart an old 12V 500 mA AC adapter, and that circuitry should be able to provide the necessary DC power to the system, and can be hooked up internally. But if I'm going to be putting an Arduino in there, I feel like I should add more functionality too, while I'm at it. Of course, I'd then need to add more controls somehow, or hook up a bluetooth module and use my phone to control and write control software for my phone or something... but I should probably just focus on the stirring for now.


You could design a housing and have it 3d printed from 3dHubs




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Melgar
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[*] posted on 2-10-2017 at 21:35


Quote: Originally posted by VSEPR_VOID  
You could design a housing and have it 3d printed from 3dHubs

I actually have the stirrer motor in there now, but hooked up to an adjustable DC power supply that's primarily for things like electrosynthesis and electroplating. The wires are running out one of the vent slits on the hotplate, and the motor was just mounted with this double-sided foam tape stuff, to keep it from rattling too much. So far, it's worked okay, but I feel like I'd need a pretty good incentive to finish fixing it.

How much do things like enclosures cost to have made? It'd probably need to be a fairly heat and chemical resistant type of plastic, for a mount that'd be inside a hotplate.




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