HP-41 Batteries

[Hans-Peter]

There are good variants to make a strong Power source even for a card reader. I have testetd a Lipo version and a double AAA version (for non card reader).
   
First preparation for all Versions:
First I took a 3mm playwood from a wooden giftbox. Then I took the spring contacts from a dead DECT phone. The best results with the glue are those with the "UHI Hart".
The small noses to hold the cover down, are replaces with a pice of alloy.
   
For the electronics I tried 5V and 6V mini step-up converters. The right one took only 7uA idle current. 5V version works but I would recomend the 6V versions (harder to find).
   
This module works from 0.8V to 5V. You can use a single cell but not with the card reader. I recomend the ENELOOP's as rechargeabel batteries.
   
If you like to use the card reader, then you have to give a higher voltage to the converter. I took a 240mAh 1S Lipo as a small Lipo chager. On the charger are two Led's. The red one means "charge" the blue one says "full". With a clear peace of plastic on the Led's, the color can be seen on the side.

Here is a Picture of the Lipo version. The AAA version is waiting for the 6V module.

The Lipo version has a charger plug on the right side of the calculator. You can use a micro charger cable to charge the Lipo.

Now, I take the HP41 to my work for a longterm test.

Best regards from switzerland