A Stirring Hack

Stirring Flask

[Oleg] of Circuits@Home and maker of the USB Isolation Board and the USB Host Shield has a new, two-part hack for his chemistry set. In Part 1 of  this hack, [Oleg] discusses the method he uses to make a stir bar spin and what types of stir bars work the best. Part 2 discusses the motor control code and circuit. Given the ample amount of capability leftover in the Arduino he used, we would like to see this stirrer paired with a heating element to have a complete hotplate/stirrer. What do you think you could do with or to improve this device?

29 thoughts on “A Stirring Hack

  1. 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.

  2. 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.

  3. How about adding some leds (IR or RGB maybe) to trigger some photo sensible liquids,temp and density sensor. Also,a tiny piece of VB linked with ur arduino could make you a perfect coffee machine for example (time control of start-end,duration and data could be logged to the pc using a write cmd on a simple txt file.

  4. 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.

  5. This would go well with the homebrew beer articles you have been posting lately. These are often used to culture yeast.

  6. 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.

  7. @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.

  8. 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.

  9. Wow never really thought of bringing arduino into the lab. The above mentioned functions would be great if one could simply enter parameters, and have the device shut off if it drifts out… perhaps I could monitor multiple experiments from the office (better air, less ether and I could drink coffee). Hmmmm I like this.

  10. Teflon (PTFE) stir bars are cheap enough on ebay that I wouldn’t bother trying to hack something as a replacement IMO.

    Great otherwise though.

  11. 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.

  12. 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.

  13. 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

  14. Fine article. Theres a lot of good info here, though I did want to let you know something – I am running Mac OS X with the latest beta of Firefox, and the layout of your blog is kind of flaky for me. I can read the articles, but the navigation doesnt function so good.

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