1.3.1-rc.1+ change to Boron solar charging (via VUSB) behavior

Tags: #<Tag:0x00007fe21f26ec48>


Hi all, I’ve updated a Boron to 1.3.1-rc.1, then 1.4.0-rc.1 to try and fix the notorious reconnection memory leak issue, and it looks like my solar charging behavior has been seriously affected.

I noticed this entry in the 1.3.1-rc.1 release notes:

My setup is a Voltaic 2W panel wired directly to VUSB and GND pins. It is rated for 340mA at 6.5VDC

My application firmware has these PMIC entries in it. These were left over from some testing I was doing early on to increase charge performance, but as you can see from the comments, I kind of abandoned that when it wasn’t needed. The unit normally recharges the 2500 mAh battery within 90 min of full sun, which is more than aggressive enough.

    //Set up PMIC chip for optimal solar charging of InputVoltageLimit = 5080, ChargeVoltage = 4208
    //If LiPo doesn't charge when connected to USB, especially with long cables dial InputVoltage back to 4840 - 4640
    //If LiPo gets too hot (ambient > 113F) or explodes, dial Charge Voltage back to 4112
    PMIC pmic;

The first unit that stopped charging was after the aforementioned firmware update, but it is a 3hr drive away so I’ve not been able to connect locally to downgrade it and confirm solar recovery.

So instead I took a precious virgin spare off the shelf, set it up as typical, downloaded the same program at firmware 1.2.1, which is what the 7 others in the field (and still working fine) are at. Connected the solar and got a nice steady, strong LED and a status of:

"source":"USB host"}

Sent version 1.4.0-rc.1 down, and charging LED immediately changed to a very dim very rapid flicker, and status poll reports:


I also tried removing the PMIC references above, but no change in behavior.

Is it possible that the surgery in issue 1846 has made the PMIC pull too much current and is now collapsing the cell, since it can supply max 340mA and not the 500mA of typical USB (new max is now 800mA)?

I’m not very good on the electrical side, so I’m going to rely on someone like @Rftop or @RWB or @rickkas7 that helped me with the original bits to chime in on that one.

Any ideas guys?


I’ve been doing a lot of Solar Panel testing with 1.3.1 and 1.4.0 lately, but with Xenon not Boron.

I don’t have a complete understanding on what all #1846 changed, but the PMIC should still obey your
setInputVoltageLimit setting. If 1.4.0-rc.1 doesn’t, then that would be problematic.

Can you try pmic.setInputVoltageLimit(5080) and pmic.enableDPDM() to see if your panel will recharge ?


It appears 1.4.0 may manually override the user’s pmic settings (as you suspected @epbwhiz), but that’s why we have Release Canidates :

This “fix” might be a step backwards for Solar Powered Borons (power critical) where the only benefit is to increase charging current to mains powered Borons (unlimited power source, IE: not power critical).

Who can we tag to answer the question:
Can we eventually set a “Solar” Flag for the PMIC to not use the 1.3.1 modifications that override
setInputVoltageLimit, causing a Solar Panel’s voltage to collapse?

Solar Panel Users actually would benefit from access to a higher setting than (5080), but dropping setInputVoltageLimit to (3880) despite the User’s PMIC settings seems detrimental.



I’d think @avtolstoy would be a good choice.


@ScruffR @Rftop We do have plans to introduce an option to disable system power manager and let the user application control the PMIC on its own completely, however not in 1.4.0. System power manager will be interfering with and overriding settings the application might be setting and it has been doing so since the introduction of this feature unfortunately.

As a workaround I may suggest trying to disable the interrupt for LOW_BAT_UC:

void setup() {
    // Delay for up to two system power manager loop invocations
    // Change PMIC settings
    PMIC pmic;

This might be needed to be executed after waking from STOP mode sleep as well.


Users already had several options to increase the Charge Current above 500 mA for special cases when required, see post: (use USB Connector, tie Data Lines, etc) and everyone could still operate remote Borons w/ Solar Panels prior to 1.3.1.

@avtolstoy , Thanks for the Reply. I’ll give that a try the next time I have a Boron on my test rig, unless @epbwhiz beats me to it :wink: .


While I can understand that the solutions outlined worked, there was still a chance even before 1.3.1 that the system power manager would override the application PMIC settings.

Another potential solution would be to listen to undocumented battery_state and power_source system events and perhaps attempt to check and modify the PMIC settings if required whenever something changes.


Thanks for the quick response fellas! I’m getting a solid charge light, and a climbing charge % !

To make the root cause more difficult to determine :slight_smile: I shotgunned all suggestions into one code update:

PMIC pmic;
pmic.setInputCurrentLimit(2000) ; 

And like I said, the battery is charging, but the result in the status message is interesting:


I’ll let somebody else worry about why the state and source is wonky.

Now to figure out which of the 5 things I changed actually made the difference…

Thanks again!


Well that was quick - the detachInterrupt(LOW_BAT_UC) is critical to this issue. As soon as I remarked it out, the charger reverted back to the dim flashing original behavior.

I’ll leave the others in as tuning parameters for performance though.

Thanks again @avtolstoy