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Tom Flatterhand · 04-30-2022, 09:26 AM

Hello everyone,

Is it correct that the HP-29C has significantly brighter LEDs than the HP-25?

Thomas

teenix · 04-30-2022, 01:24 PM

I don't know for sure, but the 29C has a direct output from the power supply into the Anode driver, where as the 25C has a 56 ohm resistor in series, so it might be brighter for this reason, or because the display modules have different part numbers, or both.

The HP-21 shows same display module as the 25C but with the same direct connection to power supply. Not sure how this brightness compares.

These 3 models have different anode drivers for the display as well.

cheers

Tony

Tom Flatterhand · 05-01-2022, 04:51 PM

Thanks Tony!

But surely there is someone here who also has both calculators, can put them next to each other once switched on and then tell me if it is so?

Thomas

**rprosperi** · 05-01-2022, 06:38 PM

One of my 29C's is indeed a bit brighter than one of my 25C's (these are handy, others are not) but I would not say 'significantly'. (Your OP mentioned the HP-25, it's not clear if you are including -25C's as well).

I'd say you need to have 100 or so mixed results that are very biased towards one model, or no difference, before you could conclude there is a specific trend, or probably well less than that if all answers are the same.

Tom Flatterhand · 05-01-2022, 06:55 PM

I could imagine that HP-25C and HP-29C actually differ less. After all, they are presumably both newer models in the context of the then newly introduced 'Continuous Memory'. I was referring to the second programmable pocket calculator from HP, the HP-25, without Continuous Memory.

I can see the difference very clearly. I attach a few comparison pictures. If you can't see it well there, I can also show you a picture with manual exposure setting, but I'll have to make it first. These two here were taken with a smartphone, where I can't dial down the exposure as much as I want, so it may not be as clear.

The reason I ask is because I want to make sure the HP-25 doesn't have a bug.

**rprosperi** · 05-01-2022, 10:30 PM

I don't have access to my non-C HP-25's at the moment, other than my unit which has been converted to a Woodstock Low Power 25E, which is not fair to compare.

My 25C and 29C are not as different as those you show, perhaps because they are both Continuous RAM designs as you suggest.

Overall I do see LED brightness variation among the ~10 Woodstocks I have, and I assume that this is just component variation and/or battery strength, and not indication that any of them have problems.

I've found that when treated properly (i.e. charging batteries outside the unit, not dropping, etc.) Woodstocks are fairly resilient and reliable.

Tom Flatterhand · 05-03-2022, 08:47 AM

Thank you for testing!

aurelio · 05-03-2022, 10:23 PM

(05-01-2022 10:30 PM)rprosperi Wrote: I don't have access to my non-C HP-25's at the moment, other than my unit which has been converted to a Woodstock Low Power 25E, which is not fair to compare.

My 25C and 29C are not as different as those you show, perhaps because they are both Continuous RAM designs as you suggest.

Overall I do see LED brightness variation among the ~10 Woodstocks I have, and I assume that this is just component variation and/or battery strength, and not indication that any of them have problems.

I've found that when treated properly (i.e. charging batteries outside the unit, not dropping, etc.) Woodstocks are fairly resilient and reliable.

I've done the same comparison and I agree with Bob, I mean I think the difference is due to the component variation and/or battery strength, (swapping or interchanging the batteries, between different calculators makes the difference). I've compared even two not continuous equal model feeded with the same battery pack and the difference is appreciable

twoweims · 05-03-2022, 10:30 PM

I have two 25 (non-c)s. One is definitely brighter than the other. I converted the dimmer one to a Panamatik LP and the brightness did not change the two still have the same relative brightness.

GreyUser · 05-03-2022, 11:26 PM

C models, non-C, doesn’t matter. The display intensities vary. Period.

The variability is in the LED assemblies, at the diode chip batch level. This is true for almost all HP led products, they have intensity code letters, even todays Avago (now Broadcom) fiber optic transceivers.

While the 21 typically got the lower intensity displays, some are more noticeably bright than others. Now, somewhat off topic, the really special displays have an HP logo as the decimal point. That’s documented in the archives, somewhere. They were in the 19C, IIRC.

Steve Simpkin · (This post was last modified: 05-04-2022 12:53 AM by Steve Simpkin.)

(05-03-2022 11:26 PM)GreyUser Wrote: C models, non-C, doesn’t matter. The display intensities vary. Period.

The variability is in the LED assemblies, at the diode chip batch level. This is true for almost all HP led products, they have intensity code letters, even todays Avago (now Broadcom) fiber optic transceivers.

While the 21 typically got the lower intensity displays, some are more noticeably bright than others. Now, somewhat off topic, the really special displays have an HP logo as the decimal point. That’s documented in the archives, somewhere. They were in the 19C, IIRC.

You have a good memory Smile

http://www.series80.org/Misc/HP-19C/