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KPage
KPage
Associate
October 15, 2018
Solved

Cant power B-L072Z-LRWAN1 with battery

  • October 15, 2018
  • 17 replies
  • 6339 views

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?

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Best answer by KPage

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.

17 replies

Tesla DeLorean
Tesla DeLorean
Guru
October 15, 2018

Check the version of ST-LINK firmware being used. V25 might have an issue holding in reset.

​

@Andrew Neil​ identified and issue with a resistor or diode causing higher current draw​.

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Andrew Neil
Andrew Neil
Super User
October 15, 2018

Are you able to "run the program" when powered from any of the other power sources?

Have you studied the schematics? They show why powering the device from the battery doesn't power the ST-Link.

As the UM tells you, the reason for removing the link is because the ST-Link doesn't get powered from the battery.

But, when you are programming, the ST-Link requires a USB connection anyhow - so it will be powered from that!

So you should be able to fit the link for programming while the ST-Link has USB power, and then remove the link to run on batteries ... ?

A complex system that works is invariably found to have evolved from a simple system that worked.A complex system designed from scratch never works and cannot be patched up to make it work.
JustMe
JustMe
Associate II
October 30, 2018

I am having a similar problem. It works fine when powered from usb but when I try with batteries the LED lights up but it does not seem to transmit anymore. I have checked the schematic and the LED comes from the '5V ' line. This receives power from the various sources through diodes. I have tried with and without SB37 and still not transmission.

I have done some more testing and found that it only works when the stlink usb is used for power. None of the other power sources seem to work. Even though they do power the pcb as far as I can tell

    T J
    T J
    Senior III
    October 30, 2018

    its just 2 batteries ? 3V not 5V...

    I cant test it easily.

    JustMe
    JustMe
    Associate II
    October 30, 2018

    3 batteries. 4.5v

    But I put the 5v in quotes because the schematic shows that the 4.5v joins the 5v line

    Andrew Neil
    Andrew Neil
    Super User
    October 30, 2018

    Shall I be pedantic and say it's 3 cells forming a battery of 4.5V ... ?

    :smirking_face:

    A complex system that works is invariably found to have evolved from a simple system that worked.A complex system designed from scratch never works and cannot be patched up to make it work.
    JustMe
    JustMe
    Associate II
    October 30, 2018

    With the linkUSB plugged in the MCU_nRST pin is at 3.3v. With any of the other supplies connected the MCU_nRST is at +- 1.5v. I have searched the schematic and can see no reason why this could happen. I am beggining to think that the schematic does not accuratly reflect what is happening on the PCB,

    Andrew Neil
    Andrew Neil
    Super User
    October 30, 2018

    It's a long time since I did it, but it certainly did run from the battery.

    But I think I only tried on battery after making all of the mods to minimise power - so maybe there's something in there that's actually required for running on battery ... ?

    Have you tried debugging with an external ST-Link (or other debug probe) while running from battery?

    A complex system that works is invariably found to have evolved from a simple system that worked.A complex system designed from scratch never works and cannot be patched up to make it work.
    JustMe
    JustMe
    Associate II
    October 30, 2018

    Not yet. At the moment I am not running the original firmware. At first I thought it might be firmware related but after inspecting the schematic there does not seem to be anything that would let the firmware know which usb plug the power is coming from for example.

    I think there must be a bridge or jumper which ST has forgotten to mention. My PCB still has all the jumper setting in their original locations.

    I have done all my testing with it plugged in to power via the link usb plug. Yesterday was the first day I tried it with 3 cells ;) powering it, only to discover it did not transmit

    T J
    T J
    Senior III
    October 30, 2018

    did you check the batteries with a meter ?

    JustMe
    JustMe
    Associate II
    October 30, 2018

    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
    KPageAuthorBest answer
    Associate
    October 30, 2018

    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
    JustMe
    Associate II
    October 30, 2018

    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

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