What does a green LED after power up mean?

[g0hww]

Me too, with the sporadic green LED on startup. Pressing the reset set button a few times will typically get past the issue, but its not a good thing. So far, I've only seen this on a Lopy4 on an Expansion Brd 2. Not yet seen on the Lopy4 on PyTrack.
This with FW 1.17.3.b1.

[MarcoBenini]

LoPy4 + Expansion board 2.0 and nothing else connected. same problem.
If I plug and unplug the USB to the pc, than the green light stays on and it not possible interaction with LoPy4.
Pressing the reset button, than it works normally.
Firmware: the latest stable version from link in documentation (1.17.3.b1).
Same expansion board and USB cable with LoPy => no problem.

[dws]

@marcobenini Did you try a high-current power supply instead of PC usb power? that solved it for me. Find a USB supply rated at perhaps 1A or more. I have a large USB battery that also works well.

[MarcoBenini]

@dws Yes, You are right, it should be a problem with power supply.
I retested with a very short USB cable and now it works, but there is always an initial "green" light that lasts about a second (that does not happens with the LoPy).

The longer USB, I tried before, is the best one I have, infact is the only one that arrives to have a stable conenction with another LoRa card I have (not PyCom).

It looks like the initial current need of LoPy4 vs. LoPy is higher, or initial powerup sequence of LoRa module is different.

Probably is brown-out detection that causes the initial green light, combined, maybe, that onboard capacitors doesn't arrive to deal with (too small or slow capacitors ?).

[dws]

@marcobenini Hopefully others here can give their opinion on why this happens. I think you are correct. I am going to purchase some high-quality USB cables for use with pycom and other micros, to avoid this in the future. If anyone here can recommend a brand of cable they like, please do.

[robert-hh]

@dws I use a 3 feet USB3 extension cable at a USB3 port, with a short adapter cable to Micro-USB. That works well. USB3 is rated at 900 mA.
The FiPys I have also show green light for ashort while on boot. As far as I know, that's just the confirmation than an firmware Image with a valid signature was found; green light for taking off, so to speak.

[dws]

@robert-hh Thanks! I never saw anything in the docs regarding the purpose of this green LED. If anyone can point to that, it would be appreciated.

[Sympatron]

@robert-hh But this would have to be implemented somewhere in the firmware and I did not find any trace of this.

[jcaron]

Does this happen when coming out of deep sleep as well, or only on the initial device start?

[MarcoBenini]

I made some other tests, the ones I can make since I have no oscilloscope, desktop lab power supply, ...
So LoPy4 + expansion board with three NiMH batteries.

1. First connection to power up => green light and than normal heartbeat blue light
2. connect power, disconnect for few seconds (5 -10 seconds) and than reconnect => no green light, than starts blue heartbeat
3. connect power, disconnect for more than 10/15 seconds, reconnect => green light and than blue heartbeat.
   I suppose that internal capacitors discharge.

Than tried with external FTDI without +3.3V connected to LoPy4.
With machine.reset() or machine.deepsleep() there is no green ligth.
My explanation, but I could be wrong, the capacitors should be fully charged.

[robert-hh]

@sympatron OK. I do not know where I found that, and cannot see it in the sources either. The only thing I found in the comments to 1.17.3.b1 was to switch of the RGB led early. So maybe it lights up for other reasons. A transition on P2 may bring the LED on. But at least the fact, that it switched off indicates the normal boot being started.