Marko Laaksonen, 18/09/2020
This is Apple M0100 mouse modification from 1992. My friend Paul was studying at the Helsinki University of Technology during the early nineties.
The University had had Apple Macintoshes and replaced their equipment base with PC:s. Some members of the ICT helpdesk / -staff had tried saving some money and had tried using those older Apple mice with those completely different type of computers (As I would recall the matter from the stories of my friend from way back then.)
The aforementioned act had resulted with a bunch of broken / inoperational M0100’s (and possibly other) Apple mice.
Paul studied the insides of the M0100 and figured out the “SNx4LS14 Hex Schmitt-Trigger Inverter” had a certain function in the mouse. The IR-led/IR-detector pulse-form is not sharp enough (LED’s are known to have a “lag” / slowness within them.) The Schmitt-Trigger SNx4LS14 provides a function called “hysteresis” which makes the waveform of the mouse output more “square-wave” -like. This can be observed also with an oscilloscope.
After figuring out the aforementioned, my friend decided omitting the Texas SNx4LS14 completely and instead of that one using separate transistors suitable for that purpose.
The build/experiment was succesfull and he got those broken mice working again!
As I now can see from the specs, no more than 200 milliamps should be drawn at +5 volts. I’ve used that kind of a modified mouse with the Apple//c pretty long periods of time and there has been no problems with it. I don’t remember if a ballast resistor / front resistor was / had to be used.
The aesthetics of the repair / build is not exactly “Steve Jobs -approved” but it works all the same. Nowadays people would probably just replace the original IC. This is still pretty interesting study of a principle in practice.
Currently this mouse is not working. There’s atleast one wire that needs resoldering.
Thanks to Marko for this artefact.
FinApple 2020 (c)
Apple II Forever.