hacking the electric toothbrush

[JimKobler]

I have discovered a wonderful and cheap mechanical oscillator: the 'disposable' electric toothbrush. The Crest model had two head regions, one that oscillates back and forth 2 or 3 mm and one that rotates back and forth about 30 degrees. The oscillation rate is about 60Hz. I plan to modify one of these for testing and calibrating some optical gear that will be used for imaging moving tissue. To best use the device, I need to track the motion of the linearly oscillating head. As a first pass I glued a magnet to the oscillating shaft in the body of the toothbrush after cutting a hole in the handle. I then placed a coil over the magnet. This provides a pretty good AC signal, but not one that is directly proportional to the movement. I would appreciate any ideas about how to monitor the position of the toothbrush head more accurately.

 

[Hero999]

I don't see the point of this.

It sounds like too much trouble to me, I'd rather build a reliable, stable and predictable electronic oscillator rather than messing around with magnets and toothbrushes.

 

[JimKobler]

toothbrush application

Thanks for the reply, but the goal is not to make an electronic oscillator but to use the toothbrush as a linear mechanical oscillator. What is needed is a sensor and some circuitry to track the position of the moving part.

 

[Torben]

How exactly do you intend to use this to calibrate equipment? If you explain the actual outcome you hope to achieve, perhaps someone can provide an easier idea.


Torben

 

[JimKobler]

I am interested in measuring the shear stresses in soft viscoelastic materials that are vibrating. The imaging system provides cross-sectional movies of the materials, which are elastic gels with high contrast particles (polystyrene spheres) suspended in them. The motion of the particles relative to each other is a measure of deformation of a material, which will tell us something about its mechanical properties. I would also like to have an independent measure of the motion of the platform that the material is sitting on, hence the question to this group. Using the toothbrush mechanism is appealing because it is very compact and easy to insert into the optics bench set-up that we are using. Thanks for any suggestions...

 

[haytham]

thank u for this information

 

[moe7404]

moe in wichita ks
you need to look at the ignition system that chrysler used in the 70s.
they used a hall effect sensor. you can get more info at allpar.com
if you realy get stuck i can help as i have worked on them a lot. its realy simple system, feel free to email me. moe7404@att.net
if any one can guess what the number in email add is about ill put your name on my wall

 

[philba]

Yeah, my first thought was a hall effect device. You want a ratiometric HE device. Allegro has a number of them. With the magnet in the right position, you should be able to determine position within the noise of the system. Noise will be an issue due to the motor.

Another thought - if you know the period and can trigger on a specific position, all the other position information is deducible. So, for example, have some sort of interrupter (photocell based) that you can use to determine period. In addition, since you know where the interrupter triggers, you know the starting point. Since the motion is sinusoidal you can compute that actual position with a pretty high degree of accuracy. This assumes that the period is reasonably stable (i.e. only changes slowly). In addition, it can be predictive so you can compensate for compute latency if you are controlling a camera or other devices.

7404 is an inverter

 

[JimKobler]

Thanks very much, Moe & Philba. I will look into the Hall effect sensors.

 

[moe7404]

moe in wichita ks
you got it philba, ill have to go to my moms to print your name out, it should be up fri. i havent got my brother printer to print in kubuntu, and xp hangs up as its starting to load. i see that you do software, my son the genius works for motorola in lawrence ks, he does software also. iam a retired machinist, boeing 25 years

 

[OrlanPark]

I'd rather leave my Electric Toothbrush the way it is. And buy an oscillator. Just keeping things simple.

 

[JonSea]

Since this post is more than 8 years old, I suspect the problem was solved long ago...or nobody cares about it any longer.

 

[JimB]

This thread is locked.
JimB