HP Forum Archive 08

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HP's LED displays when running programs Message #1 Posted by Paul Novaes on 31 May 2002, 4:03 p.m. At least for the HP-67/97 it appears to be random garbled numbers. I was curious: Is it true for other (LED programmable) HP calculators? The "garbled effect" may be space-agey, but wasn't it an awful engineering decision? I mean, it must drain the batteries very quickly. (The TI-59, for example, displays a simple/elegant "]" on the right side.) -- Paul Novaes

Re: HP's LED displays when running programs Message #2 Posted by Paul Brogger on 31 May 2002, 7:22 p.m., in response to message #1 by Paul Novaes It's true of the HP-29C, at least. I remember swinging mine in a dark room while running a loop to see if I could recognize the individual flashes. I didn't have much luck, but I thought it was displaying essentially what was shown when I single-stepped through the program. Some enterprising photographer could probably come up with an image that would help explain the behavior . . .

Re: HP's LED displays when running programs Message #3 Posted by David Smith on 31 May 2002, 9:05 p.m., in response to message #1 by Paul Novaes An HP65 Key Notes says that they toggle the display on and off with each instruction step executed. They give a trick program to hang the machine in an internal counting step with the display enabled.

Re: HP's LED displays when running programs Message #4 Posted by Ellis Easley on 1 June 2002, 10:03 a.m., in response to message #1 by Paul Novaes Also the HP Key Notes says they decided the flashing LEDs would let you know the machine was still working and take your mind off how long it was taking!

Re: HP's LED displays when running programs Message #5 Posted by Andrés C. Rodríguez (Argentina) on 1 June 2002, 11:03 a.m., in response to message #1 by Paul Novaes I once had an HP 25 (a friend of mine lost it many years ago), and I recalled that the "running program" display, while mostly random, showed some patterns. Specifically, one of the digits position showed a faint 2, 1 or 0 depending on the display mode (FIX, SCI or ENG). Other position showed a faint 2, 1 or 0 depending on the angular mode (DEG, RAD or GRD). I posted a comment about this about a month ago at this Forum, and someone was kind enough to verify it was so. (That thread seems to be archived now, but you can search for it).

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