Jack Ganssle's Blog This is Jack's outlet for thoughts about designing and programming embedded systems. It's a complement to my bi-weekly newsletter The Embedded Muse. Contact me at jack@ganssle.com. I'm an old-timer engineer who still finds the field endlessly fascinating (bio).

Smart Toothbrushes

August 29, 2018

My toothbrush has modes.

At the recommendation of my hygienist, we recently upgraded our old-fashioned simple toothbrushes to an electric model. It's a Philips Sonic Care, which she said is the only model I should get. For some reason she's down on the competing Oral B.

The thing clearly has a microprocessor in it as there are a few LEDs and it tracks brushing time. Every 30 seconds the brushing rate gets much faster for a half-second or so, telling you to move to a different quadrant of the mouth. After four such cycles the thing shuts off, which is logical since you can only have four quadrants.

I'm guessing it uses a micro's PWM output to control the brush rate. I'd really like to dissect the thing, but at $80 my wife might not be too pleased.

But recently it didn't stop after four cycles. It went into a fifth, so I've been manually turning it off, but was wondering if it would repeat these cycles forever. Mentioning this to my wife, she nonchalantly said "you must have it set to the wrong mode."

Mode? In a lousy toothbrush?

Turns out there's another switch I hadn't noticed which allows for more cycles. I'm not entirely sure what those are or the reason for this. So far, I haven't tried adjusting the modes out of fear it will enter some Twilight Zone of brushing catastrophe. Will it start brushing so furiously the thing will be like Steve Martin's sadistic dentist in The Little Shop of Horrors? Or maybe it will slyly brush a stroke or two, stopping at random intervals, provoking me to use it like a simple, non-smart toothbrush of yore.

Or will it keep going faster and faster, eventually imploding in a mouthal meltdown like a nuclear reactor's China Syndrome?

Bjarne Stroustrup wrote: I have always wished for my computer to be as easy to use as my telephone; my wish has come true because I can no longer figure out how to use my telephone.

Now I feel the same about my toothbrush.

Feel free to email me with comments.

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