Another live one!


Well ...

After many attempts over 2 years, my HP-34C finally came alive on AA's. I removed the 2 screws under in the battery compartment. Loosened the case, put the screws back in, fiddled with the batteries, got the dots to turn on, got all zeros on the display, got a Pr Error, and I know I'm more stubborn than it is ... so it finally decided to start working.

Questions: How long can it last under [whatever you might define as] normal use with AA's?.



Well you find out and tell us! Nothing better than experience.


Based on similar but not quite identical cases, I would expect at least some 6 to 8 hours of "normal" use with AA alkalines. More may be expected using a "screen saver" display mode (FIX 0) whenever possible.


re: "More may be expected using a "screen saver" display mode (FIX 0) whenever possible.

How much of the display does this turn on? I used to leave my HP35 on with just a decimal point in the display when I wanted it on, but saving as much juice as possible. I figured obviously (but perhaps, not correctly) that this would minimize the power used by the display.


I'm not too familiar with the 34C, as I unfortunately don't own one, but my guess is that a 'screen saver' mode is not necessary on the 34C because of its continuous memory. Am I wrong? Does the 34C clear some registers when turned off, e.g. the stack or LastX?

Cheers, Victor


Hi Victor,

Yes, on the 34C, it appears that the stack and last-x registers are zeroed when the calculator is turned off. I don't find this to be an issue as my likelihood of remembering what I had in the stack or last-x after I turned off the calc is not very high. I am more likely to keep track of the storage registers which are, of course, preserved.

I have compromised on the "screen-saver" strategy and decided to use it in "fix 2". The display setting is preserved. [The angular mode is not.] The mantissa option [prefix on other hp calcs] allows for momentary display of all the digits, so this doesn't present a major problem.

I plan to switch to the NiMh rechargables depending on how often I use the calculator. Like my TI-58C and National Semiconductor 835A LED calcs, I will definitely use it at least once a day. Batteries being what they are, "a watched pot never boils" or whatever.

A minor collector note - while I purchased the 58C at an antique store, the 34C was bought new probably in the early 80s, so it was a thrill to see it running again.

[At 50 percent off its $2 price tag at Saver's, a Phoenix area thrift shop, the 835A was irresistible. Of course, the 9 volt battery cost more than the calculator and the calculator is unprecedented :) ]


Certainly the single dot display (only supported on HP 35, 45, 55, 65 and 67) causes the minimum power drain. On other models, where the decimal point is "merged" with a digit position, a "1." display gives the minimum drain.

The first case (decimal dot only) turns on just one LED "segment". Further, in some models, the current applied to such segment is somehow less than the current for the other segments. Because of multiplexing, the dot is excited only 1/15 of the time, but the refresh rate is enough to fool our eyes into seeing it as permanent.

On Woodstocks and Spices, the "1." excites three segments during 1/12 of the time, so the current is not as low as in the Classics, but it is the minimum possible. I assume that individual segment currents are similar between models, but this is an unproven assumption.

You are right to remark that pressing the decimal dot key on a Classic, or the "1" key on the other LED models, is enough to reduce the display power usage to a minimum (at the expense of a stack lift operation), with no need to change the display mode, as my previous posting suggested.

The power budget for LED displays is a significative part of the total power budget for these models, so batteries will last longer when few segments are active. Apart from this, since LED show no wear over time, there is no benefit in keeping them off. Perhaps my usage of "screen saver" was not a good metaphor at all.

All the power considerations are useful for the older models, but on a 34C, due to the Continuous Memory feature, turning the calculator off (even for a short time) is always a most valid option.


Hi, I'm using AA'S on my 33E and I turn it off when it's not being used and the batteries are Alkaline ones, and they've been in the unit for 2 months. Daily use is about 1 hour off and on, as I said. Does this help you


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