What are the final specs for the DM42?

[jebem]

(12-22-2017 02:42 PM)Logan Wrote:  Thanks Bob, I do understand these concepts. However I have also seen this voltage increase such as this morning: after resting all night in the same temperature. Battery was at 2.87V. Plug it in for 15 minutes and it's at 2.93V. No calculations have been run in 16 hours, no temperature changes. Also, the three bars were right out of the box. I understand temperature could affect voltage too but it seems very coincidental. Could leaving it on USB be raising a running average of voltage measurements? So it looks like it recharged but really it was just adding 3.07V of USB or whatever and raising the average?

Interesting....
I do not own this unit and therefore I can't check the electronics diagram.

However, the voltage reading is not really being measured at the battery voltage terminals.
I think that what is being measured is the voltage at the power supply rail to the processor, because it is highly improbable that a dedicated battery voltage monitor is being used here.

So, connecting an external power source to the USB port, will raise the processor power supply a little and this extra energy is stored in the (at least) two large SMD capacitors visible in some youtube demo videos.

Removing the external power will continue to show a higher voltage for a while, because my guess is that this processor, being very efficient, is consuming very little current (how much, by the way?).

This is my best guess, unless there is a design flaw and the external power supply is being applied in parallel with the battery cell, but I don't even consider this possibility as it would be a gross mistake.

For dual power supply designs, the very minimum would be the usage of two low voltage drop rectifiers, where the cathodes are joined together and connected to the positive lead of the processor, and each rectifier anode receives a different power source. In this way, it is not possible to apply voltage from one source to another.
And because the external power source is a little higher (it must be) than the 3V of a coin cell, when using the external power source, it will in fact disable the usage of the internal coin cell.

So, how long can you see a voltage raise after unplugging the external power?