DB48X: HP48-like RPL implementation for DM42

[spiff72]

(07-03-2024 05:53 PM)spiff72 Wrote:  I have an possibly odd question.

My DM42 (running DB48x) is showing the low battery warning today for the first time. I figured that this is probably legit because the voltage indicator in the menu bar has been gradually decreasing, and it dropped below 2.6v now.

I am at work but I have a stash of crummy CR2032 batteries here that I thought I could at least install and use until I get home and put a better quality battery in tonight.

However, when I swapped in one of these suspect batteries, I still get the error message and can't use the calc unless it's plugged into USB power.

I did check the battery voltage with a multimeter and it was about 3.1V before I installed it. I just pulled the back off the calc and carefully checked the voltage while it is installed and in the "on" state (currently displaying the low voltage warning). I measure 3.15v despite the voltage level being reported by the calc in the sub-2.6v range.

Could something have changed in the latest FW version that might cause this? It seems like it's not reading the voltage correctly, but I never tried measuring the voltage in-circuit with previous FW versions.

Thanks!

To add to the above...

I checked the voltage of the battery that I removed, and it is showing about 2.78v (outside the calc - not in circuit).

And to clarify how I am checking the voltage while in-circuit, I am touching the very edge of the big round pad on the PCB that the negative side of the battery touches (very carefully to avoid shorting the probe against both the pad and the edge of the battery), and touching the battery holder to get the + side contact.

EDIT: I also tried reverting to the previous version but that didn't help.

EDIT2: I tried flashing the latest C47 and it appears to report the same voltage with the BATT? command (around 2.49v), but that firmware doesn't pop up a message about replacing the battery. With the DB48x firmware, I can't even turn the calc off to get out of that error state.

It's surprising to me that the voltage value available in the firmware differs from the voltage I can read at the battery. I will swap the battery for a better quality one when I get home tonight.