The small DC pump motors are best controlled with pulse width modulation (PWM)–an electronic controller ouputs very fast (~20Hz-30KHz) on and off signals.
I picked up a vintage analog oscilloscope on Ebay to analyze the device’s output. It came today and I was thrilled to hook it up.
And only after seeing that cool blue-green CRT come to life did I realize how my past has intersected with our current mission, and it’s a cool story.
In 1975 I won a scholarship to attend a special electronics summer camp at the University of Arkansas Fayetteville. (My single Mom drove 18 hours straight to get me there from southern Arkansas and be back in time for work. In a Ford Pinto. Thanks, Mom.)
I’m very hands on and visual, and loved learning to use an oscilloscope–despite a scary forest of knobs, it made sense to me–it converts voltages and waveforms into visual things. You can see frequencies, amplitude of waves, their shape. Knobs control the X and Y scales; these things convert the unseeable fluxes of electrons into elegantly simple plots.
And only this afternoon did I realize how this little electronics camp has come full circle–in 1975 an outreach program at the University of Arkansas taught 15 year old me to use this instrument. After 35 years (I haven’t touched an oscilloscope since then) I drew on that knowledge to develop open source tools for (we hope, with funding from NSF) wonderful science outreach programs using our models.
Photos: PWM signal on the Tektronix 425 ($230 on Ebay!); Lily poses with her new toy.
Here’s a great website on oscilloscopes and their use. The oscilloscope photo shows a PWM signal, kind of messy because we don’t have the correct probes for it yet; the upper line is ~12 volts, middle jagged one is zero volts. Each vertical black line is 2ms (so frequency would be 125Hz).