Electronic experts need help W/ Trackball mechanism

[RickM]

My wife has a very expensive sewing machine that uses a trackball for some of it's function selection. However the vertical track does not work (horizontal does work). I took it apart and it looks like the inside of computer mouse. Does anyone know how the sensor works and translate axle movement to electrical an impulse? Light, magnetic....doesn't look like a variable resistor. And suggestions on fixing....thanks!





PS How is a "Semi" sealed" LED case back lit? Is there a bulb in the casing?

[rcecale]

Hi Rick,

Take a look here. Hope it heps you...it looks exactly like what you're looking for.

This site has info on practically everything!

Randy

[island911]

I've designed equipment with those sensors.

You're right about these being just like a computer mouse. Chances are it is an off-the-shelf assembly. (for a computer mouse)

They have little light sensing quadrature chips (they sense not only the light (on/off), but the rise/fall of the leading edge (for direction))

I have seen one of these fail simply because it was poorly shielded for external light. . .sunlight would flood the sensor side.

The best thing is to look for a bad connection; then look for a replacement part. The light source could be bad, but these usually last a very very long time.

[RickM]

Great, thanks for the info. So it appears that there is, most likely, two lights and two sensors for each code wheel. This would determine direction. I agree that it is unlikely that both would fail.
I'll check solder connections and for dust. I think the sensors/LEDs are pretty well shielded by the plastic housing. This board is also pretty well sealed in the machine case as well.

Any idea of a source for the parts or a way to determine specs for them? I'd bet there comon components.

EDIT: Perhaps the parts from an old mouse will do.....

[island911]

they usually have one light (per axis) . . .and then the sensor has two pick-ups, slightly off-set (for direction)

[RickM]

The exmplae provided by Randy shows two lights.....I'll have to use my manifying light to take a close look at this puppy. Any suggestions on testing this thing while out of the machine? There are so many connectors to the board that it's impossible to jumper. For instance if I apply the proper crrent to the LED will it be visible? Is it merely a clear LED? And will the sensor develop current when detecting light?

[island911]

These parts are so common that you will be swamped looking for just the right replacement parts. You can try www.usdigital.com

[island911]

likely uses an IR LED, for the light source (and an IR sensitive phototransistor -receiving) . . so, no; you won't likely see it.