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Battery measurement calibration problem

Jaroslav Škarvada
 

Hi,

with the FW 3.0.1 (I didn't try with different version) I tried to calibrate measurement of my LiPol battery. With disconnected external power supply I pressed the black button while switching the Morserino ON, then I selected Calibr. bat., then I connected multimeter to the LIPO+ and LIPO- pins on the PCB. Multimeter showed 3.78 V, but the lowest value I am able to set through the encoder is cca. 3804 mV, which is quite OK, but why is it impossible to set lower value?

thanks & regards

Jaroslav, OK2JRQ

Willi, OE1WKL
 

Jaroslav,

I determined the necessary range from a sample of Heltec modules. Apparently yours is pretty close to one end of the scale…
But ti is not necessary to have a precision better than 3-5 % for the intended purpose, i.e. to give a rough indication about the loading status of your battery. You’re only 24 mV away from the true value, that’s an inaccuracy of less than 1%…. And I am sure that calibration at lower or higher battery levels will not bring a consistent result - teh design of the Heltec module just is not good enough for that purpose.

73

Willi

Am 12.05.2020 um 14:16 schrieb Jaroslav Škarvada <zbox@...>:

Hi,

with the FW 3.0.1 (I didn't try with different version) I tried to calibrate measurement of my LiPol battery. With disconnected external power supply I pressed the black button while switching the Morserino ON, then I selected Calibr. bat., then I connected multimeter to the LIPO+ and LIPO- pins on the PCB. Multimeter showed 3.78 V, but the lowest value I am able to set through the encoder is cca. 3804 mV, which is quite OK, but why is it impossible to set lower value?

thanks & regards

Jaroslav, OK2JRQ




Wojtek SP9WPN
 

With v2, my battery meter was working very well.
With v3 I often get "?" voltage on startup. I've performed calibration and found it almost 0.5V off. Now the voltage shown on startup is valid, however I still get "?" from time to time.
Perhaps it's worth investigating, if there is actually a bug in latest firmware?

--
73!
Wojtek SP9WPN

Willi, OE1WKL
 

Wojtek,

No, it is not a software bug, it is a (known) hardware problem:
The pin for measuring the battery is the same that is needed for activating WiFi; once you have used WiFi, battery measurement doesn’t work anymore - this state is even preserved through a software reset, and can only be changed through a hard reset (reset button, or power off).
In older firmware versions the battery indicator would always show a full battery, when the measurement was not meaningful. Now it shows the question mark to indicate that you have no valid measurement. After a hard reset it will work again.

BTW, there is a were version of the Heltec module, that doesn’t have that problem - unfortunately this meant a pin change, so it is not compatible with the M32 PCB. For teh PCBs I still have in stock, Heltec continued to manufacture the „faulty“ module especially for me (otherwise I would have had PCBs worth probably 10.000€ for the dump….). And battery measurement is a nice to have, but not a crucial functionality of the M32, so this is a viable compromise.

Once the current PCBs will be gone (July, August?), the supply of loudspeakers will also be gone (they are not manufactured anymore). So the current version of the M32 will be history. If the demand for Morserinos will still be high towards summer, I will look for a replacement loudspeaker configuration, and do a re-design of the M32 PCB, to accommodate the newer Heltec modules (with a little bit of trickery it should be possible to detect in the firmware which kind of Heltec you are running, so teh firmware could still be compatible between older and newer versions of the M32, hopefully). We will see how this goes…

73

Willi

Am 12.05.2020 um 17:13 schrieb Wojtek SP9WPN <sp9wpn@...>:

With v2, my battery meter was working very well.
With v3 I often get "?" voltage on startup. I've performed calibration and found it almost 0.5V off. Now the voltage shown on startup is valid, however I still get "?" from time to time.
Perhaps it's worth investigating, if there is actually a bug in latest firmware?

--
73!
Wojtek SP9WPN


Wojtek SP9WPN
 

On Tue, May 12, 2020 at 04:10 PM, Willi, OE1WKL wrote:

The pin for measuring the battery is the same that is needed for activating
WiFi; once you have used WiFi, battery measurement doesn’t work anymore -
this state is even preserved through a software reset, and can only be changed
through a hard reset (reset button, or power off).
In older firmware versions the battery indicator would always show a full
battery, when the measurement was not meaningful. Now it shows the question
mark to indicate that you have no valid measurement. After a hard reset it
will work again.
Oh, that explains it all.
Thanks Willi!

Wojtek