YADIYSP: Yet Another Do-It-Yourself Stir Plate

I have done several batches of beer now, and since I want to try doing a Lager or a Kölsch before winter winds down, I figured I better start making some yeast starters. And hey, another excuse for a frivolous DIY electronics project. Today I put together a stir plate. If you want to make one like this, I have itemized the parts and prices below. You would also need an erlenmeyer flask (we have a 2000 mL flask) and a 25 mm stir bar.


  1. Desktop Plastic Project Case Box 5.51″ x 4.33″ x 1.38″ $6.90
  2. Thermaltake Mobile Fan II External USB Cooling Fan $10.92
  3. SPST Small Rocker Switch $1.62
  4. USB Extension Cable (2) $7.98
  5. Neodymium Magnets 1/2 x 1/8 inch Disc $5.89

Total cost $33.31

Some disassembly required!

diy_stirplate_0002 I chose the Thermaltake fan because it is 5 volts so I can power it over USB, and it comes with a built in speed control potentiometer with a nice metallic finish knob. I unscrewed the bolts and tossed the cage and stand.diy_stirplate_0003 The potentiometer knob is just held on by tension, but it is a lot of tension. I needed some pliers to pull it off.diy_stirplate_0004

diy_stirplate_0005 There is a small clip on the potentiometer that holds it into the bracket. Depressing the clip allowed the potentiometer to be pulled out.

diy_stirplate_0006 These mounting nibs are in the way for mounting the fan.diy_stirplate_0007A quick buzz with the cutoff wheel on the rotary tool got them out of the way enough to move forward with mounting the fan.
diy_stirplate_0008 I marked out the holes and drilled them out with a 1/8 inch bit, then ran the bolts that held the cage on through the box and fan and used the nuts that came with to lock it down.diy_stirplate_0009 I am using the female end of one of the USB extensions as a power jack. Here I lined it up to the back plate to cut out with the rotary tool.diy_stirplate_0010 4 wires to a standard USB cable, Green DATA+, White DATA-, Black POWER-, Red POWER+diy_stirplate_0011 Test fitting after making the cutout. Meh… good enough.diy_stirplate_0012 Next I cut off the female end of the other USB extension cable and striped the wires on both male ends to solder them together to make a power cable for the stir plate.diy_stirplate_0013 Twisted up and ready to solder. I also used some electrical shrink wrap to make the connections and cable nice.diy_stirplate_0014diy_stirplate_0015I cut out the front plate of the project box with the rotary tool to make a place for the rocker switch.

Had to take out one of the bolts because the switch wouldn’t fit. Three should be enough, right?diy_stirplate_0016Now to wire up the power.

diy_stirplate_0017 I was going to use these handy clips, but my crimping tool is the wrong size and I just ended up butchering the whole pack of clips.diy_stirplate_0018 Oh well, more soldering.diy_stirplate_0019 Now to find a good place to position the potentiometer knob.diy_stirplate_00201/4 inch drill bit seems to be the right size.diy_stirplate_0021Fit is good enough.
diy_stirplate_0022 Hot glued the USB female power jack and the potentiometer to the case.diy_stirplate_0023 Next I centered and hot glued the magnets to the fan. The magnets are stacked 2 high.diy_stirplate_0024 It spins!diy_stirplate_0025 A test run before adding the box cover gets a good lock on the stir bar and creates the expected vortex.diy_stirplate_0026 Unfortunately, with the cover on, I can’t get a lock on the stir bar and it flies off almost immediately. I tried adding another magnet to each stack, but it presses against the top of the box and wont spin. Either way, going to have to do some more cutting.diy_stirplate_0027Ugly cut with a drill bit and rounded out with a rotary tool sanding cylinder.
diy_stirplate_0028 That’s OK, I can pretty it up with some red cellophane tape.diy_stirplate_0029 Little girls love science!diy_stirplate_0030 The colors change. It is whirling and swirling and working as expected.diy_stirplate_0031 Proper glamour shot.diy_stirplate_0032 USB A male to USB A male power cord.diy_stirplate_0033 The power jack on the back.diy_stirplate_0034 The potentiometer knob.diy_stirplate_0035 The power switch.diy_stirplate_0036diy_stirplate_0037 Rubber feet for the bottom.

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