Tinkering and Fiddling: HP Internet Advisor

As neat as the weird Pop-Out mouse is, it's not very nice to use. It's not precise, and it's way too small. I'd like to add a real mouse. The Internet Advisor has a serial port, and a serial mouse would work fine with Windows 95, but they're rare, and guaranteed to have a rolling ball at their heart. These are terrible. If I could somehow hack a PS/2 mouse into the system, I could actually have something more modern, with an optical sensor.

The Search for PS/2

The PS/2 port is a fairly old standard, and it makes sense that a 486 chipset would have one. It's relatively easy to implement. Other than power and ground, a PS/2 port has two signals: 1) a clock generated by the chipset and sent to the mouse to synchronize 2) the data sent by the mouse relaying all of the movement and button information.

If HP didn't provide the physical PS/2 connector, maybe they brought the signals out to a header that I could plug into...

First I had to figure out the chipset used to interface the 486 with the rest of the system. That's easy; it's written all over the big Integrated Circuit packages. There are four big ICs on the main board, all helpfully labeled "CHIPS". I'm old enough that I recognize the name: "Chips & Technologies".

Back when "chipset" meant something.

Some Googling gave me the functions of the ICs, and even datasheets I could download from shady datasheet websites:

F84041 (top left) - Systems Controller
F84045 (top middle) - Integrated Peripheral Controller (IPC)
F82C735 (bottom middle) - I/O Peripheral Controller
F65545 (bottom right) - VGA Controller

After digging into the datasheets, I found the PS/2 clock and data pins pins on the F84041:

After carefully placing one meter probe on both pins 101 and 102, I poked around the board looking for a beep from the meter's continuity buzzer. If I didn't find the signals brought to anything easy like a connector, I'd have to gingerly solder wires directly on the IC pins, which is not a talent I have.

I didn't find anything easy, but something easier: both MCLK and MDATA were brought out to 10k resistors, probably pullups to +5V. After finding a nice source of +5V and Ground, I'd have the four signals I'd need to talk to the mouse.

Surgery

I sacrificed a PS/2 extension cable so that I would have a socket to plug the mouse into. Then I soldered wires to the resistors pulling up the clock and data signals:

Clock (blue) and Data (pinkish) wires soldered to their respective pullup resistors

Not far away, I found a source of +5V and Ground:


A large Tantalum capacitor across the +5V rail provides power and ground to the mouse.

The whole shebang. Clock, data and power brought out to a PS/2 socket, with an intermediate connector in case I screwed up something.

Blue Smoke

Excited to test my work, I re-assembled the whole computer, powered it up... and then nothing. No display. The hard drive clicked and the floppy drive did its seek, but nothing showed up on the LCD. Then I smelled the smoke.

Unfortunately, I didn't shut it down fast enough. I had plugged in the LCD cable incorrectly, and apparently blew out the MOSFET which supplies power to it: