Visi ON PCjr Mouse

[Brutman]

I just picked up an old SummaMouse recently - an optical mouse with a DB25 connector. It also has a wall-wart power adapter.

Many of the old mice required power supplies because they required too much power to just leech power from the RS232 pins. Another interesting bit of trivial .. RS232 voltages can range as high as 12 or 15 volts, positive and negative. (Many people assume that it's just TTL levels, which is 5v.)

[OldComputerGuy]

I'm surprised they didn't draw power through the lightpen port the way Mouse Systems did since it's basically the same mouse. It would saved them some money instead of having to include a wall wart and Mouse Systems already did the engineering work for the cable.

[Brutman]

It's actually not that surprising if you consider the life cycle of a product. Normally the first revision needs to get to the marketplace fast, so it is an adaptation of an existing design with minimal changes. (The external power wart works on any system.) It's not until a later revision that companies usually try to optimize for cost by reducing part counts.

The fact that Mouse Systems came out of the gate with a PCjr version of their mouse actually is surprising; they were probably expecting to sell a lot of them.