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cheap power for the HP41C (while at desk with cardreader) - Printable Version

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cheap power for the HP41C (while at desk with cardreader) - exschr - 05-06-2011

Hi there



I want to attach external power to my 41c because I'm using the cardreader mainly at my desk. (I'm looking for options like wallplug_adaptor or clip with D-cells or the like...)

I read in PPC V7N3 (page 23) about attaching an external battery to not go through to many sets of N-cells because of the hungry CR-motor. But I'm missing some details there.
(R.W.Edelen used a modified TV cheater cable for this)

My Question:

Where can I find circuit schematic with the details I need to know to run the calc off external power while at the desk (aim: N-cell saving while running cardreader at desk)

I know that I could bidding on TAS for a recharger and an akku-pack, but I believe there are cheaper ways of using external power!



Up to now I was using the cardreader with a separate batteryclip with fresh N-cells in it. After using the Cardreader I put in the clip with the N-cells that were not anymore powerful enough to drive the CR motor but let me run the calc still some time without the Bat indicator coming on.

Thanks for hints or pointers

Roger




Re: cheap power for the HP41C (while at desk with cardreader) - Diego Diaz - 05-06-2011

Hi,

As long as you have a USB port handy (or any other stable power source for that matter), there's no need to be messing around with external D-cells, adaptors or anything else.

In fact you don't even need the 41's N-cell battery pack in most cases, (see note on Halfnuts)

Just a standard USB cable (preferable not too long), and an empty ROM module with a good connector.

- Cut the cable to an appropriate length.

- Identify the +ve and -ve wires.

- Solder the Positive wire to the module's BAT (upper right connector pin, front view -see below-)

- Solder the Negative wire to the module's GND (the upper third one, right to letf -see below-)

                      GND         BAT
--------------------------------------
| - - - - - - |
[ - - - - - - ]
------------------------------------

Module's front view

Hope this helps.

Diego.

NOTE on Halfnuts: Due to its internal circuit design, Halfnut may show the BAT annunciator permanently ON, with the power arrangement described above, if no battery pack is present; and will more likely fail to operate the Card Rader showing the "LOW BAT" message on the display. Normal operation will perform as expected though (even if no battery pack is present)


Re: cheap power for the HP41C (while at desk with cardreader) - exschr - 05-06-2011

Thank you very much!




Re: cheap power for the HP41C (while at desk with cardreader) - Dieter - 05-06-2011

Quote:
I want to attach external power to my 41c because I'm using the cardreader mainly at my desk. (I'm looking for options like wallplug_adaptor or clip with D-cells or the like...)

That's no problem as long as you have the rechargeable batterypack and its AC-adapter. ;-) However, exactly for the purpose you mentioned I use a small connector made by a friend (with much better mechanical skills than mine). It's essentially based on the back of an obsolete battery pack, but it could also be done (even easier) with a standard battery holder. Two wires are soldered to two handmade contacts (that's why the battery holder is much easier to work with), and the cable ends in a usual button-connector the way it is used on 9V-batteries. Now all what's needed is a usual battery holder for 4x AA - or maybe 4x C or D, if you like.

But that size batteries are not needed here: The original batteries in the 82120A pack had 70...80 mAh, so with current AA-size NiMH batteries you get about 30x (yes, thirty times) the capacity of the original pack. I think Sanyo Eneloop NiMH cells are perfect for this application.

Quote:
Where can I find circuit schematic with the details I need to know to run the calc off external power while at the desk

What schematics? All you need to know is the position of plus and minus, and the right voltage of course. The BAT announciator comes on as soon as the voltage has dropped to 4 V, and four fresh alkaline batteries will output something like 6...6,5 Volts. That's your range. So 5 V are fine, e.g. from four Eneloops.

Dieter