It was long ago to remember the details and indeed i cannot find a reference to the X-ray right now. We have been impressed by this fact at the time so we tested with a pen and tried it. It could detect positions with merely touching the glass and if we used a pen as a finger we could tilt it and a different selection was detected. We could not believe it either.
This is what i remember (not that i have en elephant's memory). Maybe someone with a HP16500A (the instrument was bought before 1994) full manual can enlighten us? All manuals found had the section "safety & warnings" after the index.
As far as of X-windows it was something we adored (it was used to high-end systems like SUN's Sparkstations... we always went to exhibitions to see them). Nice times...
"Voila! It worked! It wasn’t until a number of years later that I read a book with a whole chapter on this type of circuit and the methodology to design them safely."
Does one of you remember the name of this book?
Nice to read article, thanks!
The 1997 date on the user manual at
http://cp.literature.agilent.com/litweb/pdf/16500-97023.pdf makes it far more likely that this device used a resistive touch screen. Two thin layers of transparent resistive film separated by small spacer beads.
The author may have been confused by the statement in the manual "You can also operate the Logic Analysis System through an X Window interface". Those of us with no Unix exposure would be unlikely to have understood what the heck an X Window was. (My pedantic Unix-head friends would be pleased that they used the correct "X Window" rather than "X WindowS")
"I remember that instead of a touch screen this beast had an X-ray finger detector! It was brilliant, but certainly not beneficial to work for many hours in front of it. A suitable warning label (that we did not care to fully read) explained something regarding x-ray exposure."
I actually still run a DOS machine in my workshop - it drives an EPROM programmer and a couple of other old ISA-based goodies I have. (Yes, I know that makes me a real old fart!)
If you knew your I/O addresses and interrrupts, configuring an ISA card was still easier than trying to get the early PCI cards working. Plug and pray, we used to call them.
Ah, the old ISA cards. I remember when you added something like an ISA-based modem -- it took a couple of minutes to get the cover off the computer and insert the card ... then a couple of hours sorting out the interrupts so that everything worked :-)
The one disadvantage of the parallel port is that it's difficult to get data in to the PC - there are only a few lines you can use for this, not the 8-bit data bus. But for output only it's great.
You can still buy port cards for ISA bus - 8255 based giving 24 I/O points, 1 A/D Input, 1 D/A Output and 3 Timer/Counters. Handy for controlling stuff:
They also do a PCI one with 72 DIO.