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]

did you check the batteries with a meter ?

[JustMe]

Yes. They are brand new. But it also does not work from the other usb or from the external power supply.

Led7 comes on with each supply. The schematic shows that LED on the 5v line. If the schematic is correct then this should be all that is required, but clearly this is not the case

[KPage · Accepted solution]

I solved it. I removed the bridge at SB37 and inserted a jumper. So when the jumper is off it can be charged by the batteries but you cant debug it. When the jumper is inserted it is working as normal.

[JustMe]

mmm mine is still not working.

I just tested it using the vin supply and it works from there. Vin and the link usb supply both feed power to the link3.3v. So there seems to be some issue between the link supply and the rest of the board. Perhaps this board is faulty and I should exchange 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.