Bela Gem Multi stopped working all of the sudden.

Mac_Tire

Hi everyone. I was working on my project developed on the Bela Gem Multi and it suddenly stopped working.
I was testing a code to control through the i2c connection 4 STMicroelectronics NUCLEO-L432KC. I had the code uploaded to run without the Bela being connected to the computer. I connected the Bela to my Mac to lookout some datas in the monitor and it shut down and now is not booting and powering up anymore.
Can you help me understand what happened?

giuliomoro

So no LEDs at all ? Disconnect all the external wires and try again.

Mac_Tire

No, nothing at all. I disconnected all the external wires, I tried to reflash the last update and I also changed the SD card but nothing.
If I connect it to my Mac the LEDs flash one time and then nothing, the same if I power it up true an external power adapter.

giuliomoro

Try.removing the cape and connect the pb2 by itself. Does that boot?

Were you using 5V anywhere in your wiring?

Mac_Tire

I tried that and nothing. The pb2 does always the same thing, it flashes the led and then it doesn't boot.

Yes I was using the 5V from the PCB I designed to the 5V input on the Bela. I got the 5V input on the official Bela schematic, I have been working with the Bela attached to my main PCB for the last two months and I never had any issue.

I had the Bela set to run on its own. I was testing the code in which using 4 10k Ohm pots connected to the Bela analog INs, through the i2c connection, I can control 4 STMicroelectronics NUCLEO-L432KC. Yesterday I needed to check the i2c connection through i2cdetect -y -r 1 on terminal. So I went to connect the Bela through USB and it shout down giving the problem I presented at the beginning of the message.

giuliomoro

Mac_Tire Yes I was using the 5V from the PCB I designed to the 5V input on the Bela.

Where are the external 5V plugged into the Bela Gem?
Did you have both USB and these 5V plugged in at the same time?

Mac_Tire

The 5V is plugged on the J8 and the J10 connector of the Bela Gem (I recheck the connector numbers from the official schematic).
Yes, they were plugged at the same time to check the log on Bela IDLE. Operation that I did multiple times before having this problem yesterday.

giuliomoro

Those are outputs, not inputs.

The PocketBeagle 2 uses three ideal diodes (LM73100) in its power path to automatically select one of three available power sources, as shown in the simplified diagram below:

The voltage inputs are:

USB_5V is available on P1.07 and is also connected to the USB-C port's 5V pin. Valid voltages are between 3.8V and 5.5V.
VIN_5V is available on P1.01. Valid voltages are between 3.8V and 5.5V.
VBAT is available on P2.14. Valid voltages are between 3.2V and 4.6V. It is turned off if any of the others are present

VSYS is a voltage output available on all pins labelled 5V on the Gem boards. An external power source should not be connected to it directly. External power sources can be added to the on-board pool of available, mutually exclusively, power sources if connected to VSYS via a diode.

In general, the ideal diode network into VSYS selects the power source with the highest voltage and connects it to VSYS. Each ideal diode has voltage thresholds with hysteresis. A battery charger (BQ21040) is connected to VBAT and can recharge a single-cell Li-Ion or Li-Polymer battery at up to 540mA when USB_5V is available. See https://docs.beagle.cc/boards/pocketbeagle-2/03-design-and-specifications.html and the PocketBeagle 2 schematic for full details. A JST[mention part series]-compatible connector with GND and VBAT is present on the Bela Gem Multi board.

To power the board when a USB-C power source is not available, VBAT should be used for LiPo cells and VIN_5V should be used for any other power source, except as noted below.

REV A4 AND BELOW
On Bela Gem Stereo and Multi boards version A4 and below, the USB-A host port is powered directly from USB_5V. If the USB host port needs to be functional when USB-C power is not available, then an external 5V power source should use USB_5V via a diode. The diode ensures that If USB-C and the external power source are both active at the same time they are not short-circuited. The diode should have a small enough forward voltage to ensure that the voltage at USB_5V remains above 4.45V as per the USB specs. If USB-C power and the external power supply will never be present at the same time, the diode can be bypassed.

REV A5 AND ABOVE
On Bela Gem Stereo and Multi boards version A5 and above, the USB-A host port is powered from VSYS. As such, any voltage in the voltage in the valid range applied via the USB-C cable , USB_5V or VIN_5V will automatically power the USB-A port.

Mac_Tire

Thanks for the explanation Giulio. I am understanding that I made a mistake, but I have some question regarding what you wrote.
If I want to plug the Bela Gem Multi to a PCB of my own design removing the two audio wings, attaching the Bela from the J6, J8, J9, J3, J10, J11 and J7 directly to my PCB, which connection I need to use to power up both the Bela and the PocketBeagle2?

I am getting confused because the system has worked until yesterday. And in the last week the only source of power for the Bela Gem and the PocketBeagle2 was my main PCB through the connection I indicated in my previous message.

I specify again that this project has been going on for the last three months and in the last two the Bela has always worked and be powered up by my main PCB.

giuliomoro

Mac_Tire which connection I need to use to power up both the Bela and the PocketBeagle2?

Quoted from above:

To power the board when a USB-C power source is not available, VBAT should be used for LiPo cells and VIN_5V should be used for any other power source, except as noted below.

VIN_5V is P1.01. So that's the short answer. However, you likely have an A4 board, so if you need to use the USB host port while powered from your power supply, you should instead use a low-dropout diode from your power supply into USB_VBUS (P1.07) instead.

giuliomoro

Mac_Tire I am getting confused because the system has worked until yesterday. And in the last week the only source of power for the Bela Gem and the PocketBeagle2 was my main PCB through the connection I indicated in my previous message.

I specify again that this project has been going on for the last three months and in the last two the Bela has always worked and be powered up by my main PCB.

Yes, that's puzzling for me as well. I am not sure exactly what may have gone wrong there, but the fact that you had the two supplies fighting each other may have played a role in that. For there to be any trouble, USB_5V (coming from USB-C) had to be slightly higher than your 5V supply, and I see how those voltages may not be constant over time, so that the condition would not be true all the time.

Mac_Tire

Ok Giulio, thanks for the explanation. I am more and more convinced that I fried the PocketBeagle2. Just some more question before risking to damage another board. I just connected the Bela Gem Multi, without the PocketBeagle2, to the PCB I designed. The connection is made through the female header I indicated you before and it power up as usual. This is puzzling me, because if you said that the 5V on J8 and J10 are outputs, how is it possibile that the board is powering up? Through my PCB the Bela Gem Multi is receiving both 5V e 3.3V on J8 and the 5V line is connected also to J10. If those connection are output they shouldn't power up the board, right?

giuliomoro

Mac_Tire is is puzzling me, because if you said that the 5V on J8 and J10 are outputs,

They are outputs from the PB2, which are used (as inputs) by the Gem cape. What do you mean the board "is powering up"?

Mac_Tire Through my PCB the Bela Gem Multi is receiving both 5V e 3.3V on J8 and the 5V line is connected also to J10.

Wait you are also providing 3.3V??? That's a no-no. Those are generated on the PB2 and are output on the 3v3 pins. There's no diodes there, so providing 3.3V externally has an even higher chance to break things than the 5V thing discussed above. The only way you can have them generated from your power supply and not break things is to remove the 3.3V pins that go from the Gem cape into the PocketBeagle 2, but I don't recommend doing that. Just use the 3.3V from the PB2 as a source and do not provide your own.

Mac_Tire

And another question, in this scenario you think that the damage was only on the PocketBeagle2 or also the Bela Gem Multi could have been damaged since I was feeding 5V on an output connection instead that on a input connection?

giuliomoro

Mac_Tire in this scenario you think that the damage was only on the PocketBeagle2 or also the Bela Gem Multi could have been damaged since I was feeding 5V on an output connection instead that on a input connection?

I would expect only the PB2 to have been damaged.

Mac_Tire

giuliomoro They are outputs from the PB2, which are used (as inputs) by the Gem cape. What do you mean the board "is powering up"?

I mean that if I plug the Gem cape on my PCB the led on the Gem cape turns on.

giuliomoro Wait you are also providing 3.3V??? That's a no-no. Those are generated on the PB2 and are output on the 3v3 pins. There's no diodes there, so providing 3.3V externally has an even higher chance to break things than the 5V thing discussed above. The only way you can have them generated from your power supply and not break things is to remove the 3.3V pins that go from the Gem cape into the PocketBeagle 2, but I don't recommend doing that. Just use the 3.3V from the PB2 as a source and do not provide your own.

Ok. I made a huge mistake then. I don't even know how it is possible that it worked for so long. I'll buy a new pocket beagle to check and hope that the Gem cape didn't suffered from any power up issue.
Thanks for all the help Giulio!

Mac_Tire

Just another question. Since I am using the i2c connection on this design, the components on my PCB can work with the 3.3V coming from the i2c connection? I would like to clarify everything so that I can go on without any more mistakes like these.

giuliomoro

Mac_Tire the components on my PCB can work with the 3.3V coming from the i2c connection?

Yes. You can use a different 3.3V for them, just connect the two GND together in that case, and do not connect the two 3.3V together. Pullups (if you need to add more than what's already on board) can go to either 3.3V source.

Mac_Tire

giuliomoro Yes. You can use a different 3.3V for them, just connect the two GND together in that case, and do not connect the two 3.3V together. Pullups (if you need to add more than what's already on board) can go to either 3.3V source.

Ok Giulio, thanks for the support and help. I have a clear idea on how to work with everything now. I probably should have asked you before starting. But, that is knowledge and learning one way or another.

giuliomoro I would expect only the PB2 to have been damaged.

I hope so! I'm gonna order another PocketBeagle2 right away from Mouser and let you know if the Gem Cape works fine. In case it doesn't I'll order another cape from the Bela website.

giuliomoro

Mac_Tire In case it doesn't I'll order another cape from the Bela website.

They are on Mouser as well now, in case that ends up being cheaper for you.

Mac_Tire

giuliomoro
Oh, I didn't know that! Thanks for the tip