Electronics Inside a Philips Sonicare Electric toothbrush

Today a coworker of mine gave me his old Philips Sonicare toothbrush. He said it had stopped charging and would no longer work. That was a good opportunity for a tear down 😉

Lets see what makes this baby chooch….(As the great man himself said https://www.youtube.com/watch?v=lA0kiYqyBmo)

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There’s very little to this device. it seems like there’s just a micro controller running the show, like every other product. (there’s more horsepower in a toothbrush these days than an a 50 year old Supercomputer!) it probably does the following tasks( my guesstimate)

  1. Running the motors
  2. Reading user input via the two push buttons (I accidentally De-soldered one Push button, while trying to De-solder the battery)
  3. Battery charging and discharging
  4. LEDs and Blinkenlights (Coz humans love ’em )

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Quick hardware analysis

A quick analysis of the PCB shows a micro controller(PIC16F726 to be precise) . Q1 seems to be a dual P channel MOSFET ( marked as ISC 6981D ). Q2 is marked AO8808A a dual N Channel MOSFET. The MOSFETs formed an H bridge which drives the “Ultrasonic motor” which I plan to get to run soon. then there’s a few sundry(read boring/uninteresting) components which probably are there for over voltage protection, an LDO, Li-Ion battery charger Etc. (High Res Image of the PCB ).

Then there seems to be 6 test Points which are conveniently labelled for easy debugging( or hacking I guess!) I’ll probe those and see what they do probably try out a few common baud rates and see what the Micro spits out. There are plenty of test points on the PCB that should include the programming pins for the micro as well.

That’s pretty much it for the electronics side of things.

Then there are other things like the Motor, A AA size Li-Ion battery, a charging coil. The coil probably forms an air core transformer with the charging dock, but I;m still not clear on how it is rectified back in to DC for charging the battery, with so few components and no bulky capacitors on the PCB.

I’ll probably power up the micro controller and see whats being sent out over the UART. Next on my To-do list would be to get the motor running and after that i would like to check out how the charging subsystem works with the weird air core coil arrangement. The weekend is fast approaching, so this guy should keep me busy for a good part of the weekend.

 

Special Thanks to Alex for donation :)

 

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