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Can a user measure voltage with the 41-C series?
04-19-2015, 03:33 PM
Post: #1
Can a user measure voltage with the 41-C series?
On the HP-41, does it have an internal voltmeter that triggers the BAT symbol at a set voltage? Or is it simpler than that?

I have been wondering if there was a way to access the internal meter to display the battery voltage before the BAT annunciator appears. I don't recall reading about this years ago when my calculator was new, and I am not spotting anything now as I am reading archived material.

It would be useful to have access to a "fuel gauge" of sorts. I have started running NiMh batteries and expect that the "5-15 day" life mentioned in the manual is a lot shorter with NiMh. I keep a fresh set of spare alkalines with the calculator in case the BAT annunciator appears. I'm not ready to trust to a second set of NiMH for backup.
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04-19-2015, 07:17 PM
Post: #2
RE: Can a user measure voltage with the 41-C series?
I'm sure it's a simple comparator, basically a 1-bit A/D converter. When the voltage falls below the threshold, the annunciator comes on. I think the only reason to use rechargeable batteries though is if you run the card reader or bar-code reader a lot, or have a 41CL. On alkalines, I used to get two years of battery life with regular use, and it seems to have gone down to about six months after I got the double extended memory module. I can go long periods without having to think about recharging. My annunciator comes on at 1.2V, which would mean it would be on even for fully charged NiCads.

http://WilsonMinesCo.com (Lots of HP-41 links at the bottom of the links page, http://wilsonminesco.com/links.html )
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04-19-2015, 09:15 PM (This post was last modified: 04-19-2015 09:25 PM by TASP.)
Post: #3
RE: Can a user measure voltage with the 41-C series?
I probably couldn't put my hands on it right now, but I have a very similar voltage detector pen to this:

http://www.buyincoins.com/item/3476.html#.VTQZEiFViko

(I'm not pushing anyone to buy it, just an example of the technology available)

Anyhow, these things are SUPER sensitive. I can unplug an extension cord, and by using this pen tell which prong was the 'hot' as opposed to the 'neutral' just from the residual charge left on the wire.

I don't know how finely graded this technology could be made, these pens as made to distinguish 12V, 120V and 240V. The device has NO internal battery!!

If it is just a matter of scaling resistors (I don't claim to know how the pen works in regards to it's unbelievable sensitivity, the display is high electrical resistance LCD technology) a similar device could be made for the 4 to 6V range, and with the low current draw, the device could be a tiny strip taped on a calculator and reading out the batt voltage full time and not noticeably shorten the battery life.

2speed HP41CX,int2XMEM+ZEN, HPIL+DEVEL, HPIL+X/IO, I/R, 82143, 82163, 82162 -25,35,45,55,65,67,70,80
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04-19-2015, 10:11 PM
Post: #4
RE: Can a user measure voltage with the 41-C series?
(04-19-2015 07:17 PM)Garth Wilson Wrote:  I'm sure it's a simple comparator, basically a 1-bit A/D converter. When the voltage falls below the threshold, the annunciator comes on. I think the only reason to use rechargeable batteries though is if you run the card reader or bar-code reader a lot, or have a 41CL. On alkalines, I used to get two years of battery life with regular use, and it seems to have gone down to about six months after I got the double extended memory module. I can go long periods without having to think about recharging. My annunciator comes on at 1.2V, which would mean it would be on even for fully charged NiCads.

I find that I am running my rebuilt card reader and the wand a lot right now, but that should be tapering off as I have most programs documented now. I probably was overzealous buying the rechargeables. I've been checking state of charge with voltmeters, I was just thinking that being able to do that on the calculator itself would be useful.
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04-20-2015, 05:51 AM
Post: #5
RE: Can a user measure voltage with the 41-C series?
(04-19-2015 07:17 PM)Garth Wilson Wrote:  I'm sure it's a simple comparator, basically a 1-bit A/D converter. When the voltage falls below the threshold, the annunciator comes on. (...)
My annunciator comes on at 1.2V, which would mean it would be on even for fully charged NiCads.

For the record: the BAT annunciator in my HP41s comes on at approx. 1 V per cell, which is the point where NiCds and NiMHs can be considered discharged. BAT does not appear with properly charged NiCds or NiMHs unless they are nearly depleted.

(04-19-2015 10:11 PM)4ster Wrote:  I've been checking state of charge with voltmeters, I was just thinking that being able to do that on the calculator itself would be useful.

You cannot check the state of charge of a NiMH or NiCd battery by determining its voltage. OK, if the battery is close to empty this might work, but else the voltage is nearly the same from almost-freshly-charged to almost-empty.

Dieter
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04-20-2015, 01:35 PM
Post: #6
RE: Can a user measure voltage with the 41-C series?
(04-20-2015 05:51 AM)Dieter Wrote:  For the record: the BAT annunciator in my HP41s comes on at approx. 1 V per cell, which is the point where NiCds and NiMHs can be considered discharged. BAT does not appear with properly charged NiCds or NiMHs unless they are nearly depleted.

(04-19-2015 10:11 PM)4ster Wrote:  I've been checking state of charge with voltmeters, I was just thinking that being able to do that on the calculator itself would be useful.

You cannot check the state of charge of a NiMH or NiCd battery by determining its voltage. OK, if the battery is close to empty this might work, but else the voltage is nearly the same from almost-freshly-charged to almost-empty.

Dieter
Good points. So, for those of you that run NiMH in your HP-41s, what is your battery cycle strategy given that the BAT annunciator is not really useful with this type?
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04-20-2015, 09:23 PM
Post: #7
RE: Can a user measure voltage with the 41-C series?
(04-20-2015 01:35 PM)4ster Wrote:  
(04-20-2015 05:51 AM)Dieter Wrote:  For the record: the BAT annunciator in my HP41s comes on at approx. 1 V per cell, which is the point where NiCds and NiMHs can be considered discharged. BAT does not appear with properly charged NiCds or NiMHs unless they are nearly depleted.


You cannot check the state of charge of a NiMH or NiCd battery by determining its voltage. OK, if the battery is close to empty this might work, but else the voltage is nearly the same from almost-freshly-charged to almost-empty.

Dieter
Good points. So, for those of you that run NiMH in your HP-41s, what is your battery cycle strategy given that the BAT annunciator is not really useful with this type?

While I don't own a 41 (yet, soon though!) I do use NiMH batteries in many devices and I find that *ALWAYS* having fully charged, low self-discharge batteries handy for each device is usually the way to go. Most devices will operate fine and won't show the low-battery warning until the battery is actually low with NiMH types, but you have precious little time to change them unlike with alkalines.

Many people are cheap and decide to get the regular, non-LSD type NiMH cells which lose 1/3rd or more of their charge each month just sitting there. I believe the use of these less advanced cells are the major cause for the rumor that all NiMHs perform poorly.
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04-20-2015, 09:42 PM
Post: #8
RE: Can a user measure voltage with the 41-C series?
(04-20-2015 09:23 PM)Sukiari Wrote:  Many people are cheap and decide to get the regular, non-LSD type NiMH cells which lose 1/3rd or more of their charge each month just sitting there. I believe the use of these less advanced cells are the major cause for the rumor that all NiMHs perform poorly.

Good luck finding N-size LSD NiMH cells.

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