PWM Modulator for the Magnetic Stirrer

The last time I was working on the Magnetic Stirrer I was using a Laboratory Power Supply to modulate current to a DC Motor, and then was stuck there, looking for a more suitable motor, and a cost effective way to modulate power to the motor.  To build copies I need to have an affordable way to modulate power because not everyone will want to buy a couple hundred dollar Power Supply for their Magnetic Stirrer.  My solution for this is Pulse Width Modulation, and a cheap DC Motor.

The Motor is salvaged from an old Ryobi Drill.  Its a common brushed DC Motor which are very cheap now.  Most Motor Technology has moved on to Brushless Motors, and Stepper Motors, and the Brushed Motors are the cheapest technology now.  The Drill used a PWM Power Control scheme, but had it integrated into the Trigger for the Drill which was a spring loaded mechanism.  For a cabinet top kitchen appliance I need a power switch, and a dial speed control, something that can be set, and left running without continuous pressure on a trigger mechanism.  In the above photo you can see a toggle switch, and the potentiometer handle.  Also notice that on top of the plexiglass there is a magnetic spinner spinning.

I used the venerable NE555 Timer IC that gets used for all sorts of pulse control, and modulation schemes.  This Timer was introduced by Signetics back in 1972, and is so versatile that it is still very popular today.  Previously I had made some very sophisticated PWM Power Contollers using PIC Processors, but for this project I wanted cheap, simple, and easy, not to mention quick, and dirty.  Well, yeah, this analog timer is dirty.  Its got a scratchy potentiometer which makes the PWM intermittent, and it also doesn't span to full 5 to 95% of the PWM range.  The motor also stalls at the end of the potentiometer throw.  Caveats to Cheap, Quick, and Dirty.  But it makes the spinner spin right?

Another caveat to using a "cheap" motor is a massive inductive kickback when the brushes break contact with the armature.  The motor is generating almost 70 Volt inductive kickbacks.  I managed to pop one of my NE555 Timers because of this.  I think it was an older one that didn't have freewheeling diodes on the output.  For the circuit values I picked a "off the shelf" schematic from the interwebs, above.  I did have to spend a little time debugging it, but overall it worked good.  Now my little Magnetic Stirrer is working good, and it doesn't need my laboratory power supply to run it.  The original intent for this stirrer was to stir the Wort for Home Brewing.  Lets make High Gravity Lager...

Clean Space

I worked on the Garage a little this weekend.  I was able to clear off one of the workbenches, and make some clean space.  Also got to clean off the Tool Box, organize all the crap that was sitting on top of it.  I closed a few projects like the Smoke Detector, and that pile of slightly used AA Batteries.  I found a under cabinet LED lamp that runs on AA Batteries, so it can be used to deplete those used batteries.  Also illuminated the new clean space...