Ball Mouse Insides and Identifying the Parts.

Martin_H

My neighbor had some old ball mice gathering dust, so he gave them to me and I took them apart. Inside there's some good parts, like three IR diodes (one terminal marked red), three IR photo transistors, shaft encoders, a wheel with a built in shaft encoder, headers, and a cable. I see robot wheel upgraded encoders in my future.

Here's what it looks like:

These are square diodes, so there's no flat side, is there an easy way to avoid identifying the cathode and anode? Since the diodes are clear I've heard that even if they're not marked their innards will tell you what's what.

What I think are the photo transistors have three leads. Which makes me thing they might be something else. Any tips on identifying what they are?

Worse case scenario I use a regular IR photo transistor since I have a bunch of them.

Also, does the size of a phototransistor effect sensitivity or is that a packaging issue? I have some 3 mm ones and I was wondering if they are less sensitive than the larger size.

Phil Pilgrim (PhiPi)

The three-lead "phototransistor" is more likely a two-output quadrature detector pair, since you need quadrature detection to detect direction.

BTW, did your neighbor use his mice in a cleanroom? I'm regularly having to disassemble the mouse in my office to tweeze cat hairs out out the wheel encoder when it stop responding.

-Phil

Leon

I use an optical mouse which never needs cleaning, and doesn't need a mat. I've heard of people using the sensors from those for interesting projects.

I didn't have any problems with cat hairs in my old-style mice, perhaps because Burmese aren't too bad in that respect. I used to get a build-up of dust on the shafts where they contacted the ball, which I scraped off from time to time. I've got the innards from an old ball mouse somewhere waiting to be used.

Martin_H

Phil, that makes total sense. I'll see if Googling that yields anything.

BTW The mouse was circuit board was cleaned before the picture. You don't want to see the ball or roller!

GordonMcComb

Phil, there's an easy solution to the cathair problem. Use an optical mouse. Have you heard of those? (For lurkers, that's an inside joke.)

Martin, I've tried several to use the encoder wheel out of mechanical mice, but some things are just too small for aging eyes. You might have better luck with that little stuff.

-- Gordon

Phil Pilgrim (PhiPi)

Leon, Gordon,

Mine is an optical mouse, too. It's the scroll wheel encoder disk that gets clogged with cat hair. How it gets in there is a mystery, since the bottom of the mouse is enclosed except for the small sensor hole. (I suppose I should check my Firefox cache in the morning to see what Browser's been up to while I sleep. )

-Phil

Leon

I'd forgotten about that scroll wheel, although I use it all the time. I've never had any problems with mine, it's a cheap Trust MI-2150.

Martin_H

I found an illustration which shows how to identify the cathode using the anvil which is clearly visible in these square IR LED's. I've Google and found several pages of people re-using the quadrature encoders directly, but it looks like to much trouble. I have some 3mm IR photo transistors which should work fine with that wheel and IE LED.

Heater.

An IR LED is a diode. So you can determine it's polarity by trying to run some current through it in both ditections. Just apply 5v through 1k series resistor and measure the voltage drop accross it.

Leon

I have a DVM with a useful diode test setting. I think it puts a constant current through the diode and displays the voltage across it.