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I have a battery operated toothbrush that I want to generate notes with using PWM on the motor. The microcontroller used is an Arduino for testing and am able to get a bare motor to generate tones. I am using 3/4ths of an H-bridge so I can stall the motor, one terminal is positive and the other is both positive and negative.

The problem is when connected to the toothbrush, the brush head does not seem to stop fast enough to generate a tone. I am assuming that there is too much potential energy in the brush head to keep it from stopping through the PWM.

Has any one else tried something like this with any success? Does this seem like an impossible task?

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  • \$\begingroup\$ youtube.com/watch?v=Kh2AWswAMvw \$\endgroup\$ – abdullah kahraman Mar 5 '13 at 17:25
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    \$\begingroup\$ This will be so cool if it works! Is the bare motor that generates tones the one used in the toothbrush? you should be able to run at a low enough frequency that the motor does stop, even reverse. Ramp up to see what the cut-off might be. \$\endgroup\$ – Bobbi Bennett Mar 5 '13 at 18:37
  • \$\begingroup\$ I am modulating the power to the motor in the brush through the PWM. But using less power to the motor might work - I have been using full power so far. \$\endgroup\$ – Louis Mar 5 '13 at 19:59
  • \$\begingroup\$ I aslo wonder if your 3/4H bridge is actually breaking the motor. See electronics.stackexchange.com/questions/56186/… \$\endgroup\$ – Bobbi Bennett Mar 5 '13 at 21:40
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    \$\begingroup\$ Have you tried singing and brushing at the same time? It's more eco-friendly... seriously this sounds fun and will you post the circuit and code when you are sure it works? \$\endgroup\$ – Andy aka May 6 '13 at 17:24
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The ability of a motor-driven assembly to "sing" will depend in substantial measure upon the construction of the drivetrain, the amount of stall torque available, and the thermal characteristics of the motor. In some cases, the amount of heat that can be dissipated in the windings of a motor which is driven with a square wave when one is trying to make it "sing" can exceed that of an immobilized motor which is fed constant DC of the same magnitude, and depending upon gear construction and backlash the voltage required for a 400Hz square wave to destroy a motor may be lower than the voltage required to make a readily-audible 400Hz noise.

I would guess that a typical toothbrush which is run by a DC brush motor will probably use plastic gears in its drivetrain. Plastic gears often have a small amount of elasticity which is good for longevity and smooth operation, but which would likely absorb much of the audio-frequency energy you might try to put through them. You could try driving the toothbrush with an AC waveform and see what happens, but it may be impossible to get good audio coupling.

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Try modulating the power to the brush instead of the frequency. I'm gonna guess the sound from the brush comes from how fast it is running, so slow it down for lower pitch.

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  • \$\begingroup\$ re downvote. Sorry. This should have been a comment. \$\endgroup\$ – Bobbi Bennett Mar 5 '13 at 18:34

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