|HP-35 keyboard technology|
Message #1 Posted by Joerg Woerner on 15 Jan 2004, 12:39 p.m.
Dear Calculator collectors,
during my researches about the HP-35 vs. SR-50 battle I noticed the clever approach of the HP-35 keyboard construction.
Tracing back the TI history of calculators you always have to start with the Datamath / SR-10 calculators. The first keyboard construction was the Klixon(TM) type with its well-known snap-action switches. It uses discrete gold discs mounted in a plastic frame on a printed circuit board and a thin and adhesive foil to protect against dust and other environmental conditions. I placed some pictures here: http://www.datamath.org/Story/Klixon.htm.
The SR-50 removed the plastic frame but still uses these snap-action discs. The famous keyboard problems started, when Texas Instruments introduced the TI-30 keyboard type with small wires and stamped, silver discs covered by black insulation foil.
Funny to know that the earlier TI-1200 keyboard with gold wires was much more reliable, but this is the art of cost reduction. Find some X-RAY pictures of the TI-30 keyboard here: http://www.datamath.org/XRAY.htm.
Hewlett Packard started with the HP-35 keyboard - a design with stamped contacts snapping against gold surface of the printed circuit board (PCB).
Today both HP and TI use Chinese keyboards but what happened between ?
I view most pictures of this HP-Museum but couldn't trace the way of HP calculators keyboards.
What I found up to know:
Second generation (HP-27) Discs against gold contacts on the PCB
Third generation (HP-31E) Experimental design followed by discs and gold contacts on the PCB (This looks really similiar to the SR-50).
Fourth generation (HP-11C) Discs against gold contacts on the PCB
Now my questions:
What was the reason to change from the simple but reliable HP-35 construction to the discs # PCB solution ?
What type of keyboard was used with the HP-41C and the later Pioneer series ?
What type of keyboard do you prefer ?
Do you "feel" the difference between a HP-35 and e.g. the HP-27 ?
What was the keyboard behavior of the HP-31E series "experimental design".
Thanks in advance for your comments.