Those of you who are sarcastically going to mention arduino to be funny, just STFU now and not bother posting.

I guess you could add measured amounts of fluid or solids through a hopper,pneumatic,or hydraulic means ;controlled by the remaining functions and programming space left on the Arduino.There are many things at your disposal for that particular application.

It is a very useful project to use together with the pHduino.

http://code.google.com/p/phduino

It is getting easy to mount a Chemistry Lab at home.

Congratulation.

OLeg have you tried using a stronger bar magnet?

Mine has almost no control and it still couples pretty well.

I realize you are doing it for the fun of exploring motor control and thats cool by me.

Coolblades – you are using stack of neodymium magnets in your stirrer, correct? They don’t last very long being placed into corrosive liquids:-).

Yet another motor driven magnetic stirrer. I’d like to see someone build a vastly more efficient solid state version. Use a simple rotating magnetic field: no moving parts in the base at all. I’d do it myself if all my previous projects involving electromagnets didn’t fail miserably.

I made a stirring plate a few years ago out of an old computer fan with the fins cut off and the magnet from a hard drive spliced with the line of a charge adapter for something that broke. I tried a few materials for the top surface, but only glass worked properly. Once the balance was set the thing ran beautifully. I purchased a stir bar, and “borrowed” a few from school. This is still the only stir plate I own, and I use it very often. This was one of my first real hacks, and I was proud of my ingenuity.

@Rachel : how would a static version be more efficient ? Generating a magnetic field needs lots of current, here you benefit from the magnet’s field, you just need to rotate a small motor.

The idea to use the µC to detect when the bar stalls is pretty good. Apparently Oleg hasn’t gotten to it yet, I wonder how it will go.

Here’s how I make my stirring bars : a small cylindrical magnet (2cm*3mm) in a piece of heat shrink, with a 1mm wide rim made of scotch tape in the center to lower friction. Works pretty well.

A nice addition would be to use a Peltier element to add heating/cooling capability. The fan would then double as heat extraction device.

It’s more efficient because it doesn’t need to turn the relatively massive motor spindle, and lose energy from its bearings. And with no moving parts, it’s much more durable and longer lasting. It can be made very thin too.

Aside from the electromagnet design, it should be fairly easy to male. Simply rectify the AC line current, and pulse it through the coils with some big MOSFETs.

As for making stirring bars, few materials other than glass or teflon will stand up to harsh chemicals. I once tried sealing a neodymium bar magnet in glass tubing, but I foolishly neglected the Curie point of the magnet and ended up with a useless glass lump.

And you should use teflon to coat your stir bars, easier to clean, longer lasting and stable in almost anything.

Hello,
I see this blog. I appreciate your information. It is very useful information. Thank you so much…

While a simply LM317 could adjust the speed, I too think it’d be neat to rig all sorts of sensors into the Arudino, possibly an array of stirplates for automated…um…mixing and heating?

THEN use it to give out status updates so you could be comfortably sitting in your office, monitoring it rather than the lab, as BuudhaFW stated.

It’d be real neat to measure turbidity(?) and temperature and adjusts based on a profile. (I can think of yeast starters benefiting from this a lot!)

@eutatic

The stirplate can be sealed to keep any vapors from entering. After all, it’s only be used to spin a magnetic field.

I’d write a simple PID controller to run a power resistor/thermocouple and get sophisticated temperature control. Throw a peltier in there too and get very flexible control.

Hehe, nope mine isn’t used in corrosive liquids. But I’m sure you’ll figure out a way to beat that.

It still seems like the main issue is the magnet decoupling with the motor. If that’s the main issue making your motor slow down won’t make it stir any harder.

I think your application would be cool for a magnetically coupled rotor in an underwater vehicle. In fact hurry and wrap this up so I can “borrow” your design. j/k

I agree with teflon coating.