I've been thinking about building a stir plate for a while and reading about the Brulosophy yeast starter harvesting method gave me a little push to do it. Being the miserable sod that I am, I like to do things as cheaply as possible, so this is how I built my stir plate for under a tenner. Actually it cost me about £6 but I had some stuff lying about the house which I was able to use. So this is what you need, all available from eBay: A 12 volt power supply - £2.19 A 12 volt PWM controller - £1.37 A 12 volt 92x25 mm CPU fan - £1.40 A couple of 8x5 mm neodymium magnets - £0.99 A handful of M3.5x50 screws and nuts - About a quid from local hardware store Lastly you need an enclosure, this is where a little ingenuity comes in. I've seen these made from all sorts of things, cigar boxes, lunch boxes, tupperware, lego. Anything that is sturdy enough to support a couple of kilos will do, preferably non metallic because it'll interfere with the magnets. Google homemade stir plate for some inspiration. I used an old soap box which I found in the house. It's not quite as manly as those cigar box stir plates, but you have to admit it's pretty If you can't find anything at home then an electrical adaptable box from B&Q will work well. So once you have all the parts, mark the holes in the fan and PWM and install the screws through the base like so, this allows the fan to be height adjustable so that you can get the magnets as close to the lid as possible. Drill a small hole for the power cable, cut the connector off, insert through the hole, connect to the "supply" side of the PWM. Connect the fan to the "load" side then mount both the fan and PWM. Stick two magnets on the center of the fan, one positive up, the other negative up. I used gluedots to stick the magnets The center of the magnets should line up with the ends of the stir bar like so: Put the lid on, plug in and switch on. If required adjust the height of the fan, the magnets should be nice and close to the lid without touching. Test with stir bar in an erlenmeyer flask. I find it's best to turn the speed right down, switch on, then slowly ramp up the speed until it gets to where you want it. This is it in action: So there you have it, a stir plate for about £6, and very pretty too Edit to add: After a few uses I upgraded my stir plate from the soap box to a chocolate box. I found that the structural integrity of the soap box was becoming rather compromised. It was sagging a little in the middle meaning the magnets were rubbing on the inside making a very irritating sound. Also it wasn't waterproof, so I had concerns about the starter overflowing onto it. I also couldn't get rid of the lavender smell from it which was annoying when trying to have a sniff of the starter. The new one isn't as pretty but much more sturdy and made of plastic so should last a bit longer.