Cant power B-L072Z-LRWAN1 with battery

[KPage]

We recently received our B-L072Z-LRWAN1 but are not able to run the program while batteries are plugged in. In the datasheet it says that we need to remove SB37 to accomplish this. But then I cant program it anymore? How can I use the board with battery only and still be able to program it?

[T J]

there is no external pull up on the nRst line in the schematic,

there must be an internal pullup..

MCU_nRst is a pull down button, requiring a pullup somewhere...

could you add a resistor to JP10 pin 1 ? to pull up the MCU_nRst line...

[JustMe]

Ok I figured it out.

Even though I thought I had removed sb37 it was still making contact. :flushed_face: Although in the doc it seems to imply that the bridge removal is more to save battery power. But it apears that with the bridge in place, only link usb power or vin will work.

Thanks for the help

[Andrew Neil]

The doc does say that the reason for removing SB37 - ie, for disconnecting the RESET line from the on-board ST-Link - is because the ST-Link doesn't get powered from the battery.

Therefore, with the link in place, the un-powered ST-Link will be holding the RESET line.

[aperles]

I'm stuck with the same problem.

SB37 removed, the voltage on CN13 is correct (3.3V) and my firmware runs till I try to send data.

Has anyone found the problem?

[Andrew Neil]

That's not the same problem, then!

The problem above was with it not powering up at all.

In any radio system, "runs till I try to send data" most likely indicates that you have a weak power supply - it's enough to (just) run the processor, but can't cope with the large peaks required by the radio transmitter.

You should probably start a separate thread giving full details of how you've got the board configured, how you're powering it, and what software you're using.

Give a link here to your new thread;

include a link in the new thread back to here.

[aperles]

I've found a provisional workaround.

I'm using the examples provided by St for this board, LoRaWAN examples work perfectly but SigFox examples freeze.

I'm using the workaround proposed in https://ask.sigfox.com/questions/7717/cmwx1zzabz-blocks-on-tx-start-unless-pa2-and-pa3-a.html and things started working. It is related to the LPUART.

[REste.1]

I have the same problem. Opening the SB37 the board continue not transmitting.

[PMART.11]

Good morning.

I would like to know if someone has solved the problem because I have the same problem and I have already tried a lot of things. The program cannot be operated with any other power source than the USB. However, the LED07 is powered on with all 3 batteries.

Thanks a lot !

[Andrew Neil]

@PMART.1​ "I would like to know if someone has solved the problem"

What problem, exactly?

Multiple posts above have said that removing SB37 (as the User Guide instructs) fixed their "problems".

@aperles​ had a completely different problem - and posted the workaround to that problem.

[aperles]

Hi,

@PMART.1​  As Andrew comments, I've solved this problem by changing the configuration of the LPUART. If you use the workaround of connecting directly the PA2 and PA3 to +Vcc is too aggressive and you could burn out the micro.

That being said, consider that the Murata cmwx1zzabz module is suffering from a shortage, so developing based on this is not a good idea right now.

If you seek dual Sigfox-LoRaWAN operation, then I suggest considering something based on the STM32WL series.

Best,

�?ngel

[Andrew Neil]

Having made mods to run on battery / get minimum power, here's a post on how to reconnect the ST-Link for programming & debug:

https://community.st.com/s/question/0D53W00001XvfJtSAJ/restore-stlink-connection-on-bl072zlrwan1