Low-Power Boron LTE, using the EN Pin


Yes, the Boron can still recharge the Li-Po while it’s disabled (Shutdown) with the EN Pin.


What if the charging current is initially applied while the Boron is disabled? I can only seem to get the charge indicator light to common if I plug in the usb BEFORE the device gets disabled…


That wont work, as you discovered.

Here’s my understanding:
While operating, the PMIC decides if all the requirements are met for a Charge Cycle.
Once started, that Charge Cycle will continue even after a EN pin Shutdown, until the Cycle is completed or interrupted. The Boron will need to Boot before another Charge Cycle is started.

For instance: A Solar Boron will continue to recharge after EN pin Shutdown until the Panel Voltage collapses (significant Cloud Cover).

[Edit] But if your project has a Power Source Available for recharging, why not just use Sleep Mode instead of EN Pin ? The Boron can Sleep @ < 1 mA.


What’s interesting is that I can get the charge light to come on after the device is disabled when I plug in a usb powered by a wall charger… but when I plug in the usb from my Mac the light doesn’t come on…

Yes I’ve been looking at stop mode sleep vs this enable pin… hitting the enable pin just seems to be more efficient.

My devices are solar powered and go out in some remote places. They read a lot of sensors that can draw decent current. Also in some locations like northern Canada, there may be a number of days where I can’t charge the batteries because it won’t get above freezing. Using the enable pin will virtually ensure that I will never have a power failure.

I saw your thread about the sleep current in stop mode, and it looked like you could get down to 1.2mA… have you found out how to get any lower since?

Thanks for all this info!


I’ve never noticed that, but I just tried and confirmed.

My Guess is that during EN pin Shutdown, the PMIC reverts to it’s default/basic configuration.
The results would suggest that the Minimum Voltage or Current isn’t being met with a Computer USB port, but can be met with AC/DC charger, which makes sense.

But I seem to recall confirming that the user defined PMIC settings were obeyed after EN Pin shutdown… at least back in 0.9.0 firmware days. I could be remembering incorrectly.

System Power Manager can now change all your PMIC settings behind the scenes now, which significantly hurts Solar Powered Borons. I’ve paused my work with Solar Boron’s for now until that’s addressed. Most of my long term testing is invalid now.

Of course, a 12V Panel charging a SLA is still a good option if you have the space.


I thought if we called this:

(credit to @avtolstoy)

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

That would make the system retain user defined PMIC info?


Correct, but I don’t have any idea what other implications that has.
That Interrupt might be used for Li-Po safety, such as the safe trickle after an accidental over-discharge, etc.

It’s fine for testing, but not something I’m comfortable with for deploying to an actual Client location.


Good point. I wish we could get some clarity on the PMIC issue. I don’t really want to switch back to the electron form factor. Even though it’s a great device.


I’ve done some digging today, and apparently detaching the Interrupt shouldn’t cause any unforeseen problems. I’m going to ask a few questions in the previous Thread dealing with detachInterrupt(LOW_BAT_UC) and Solar Charging a Boron later today.
[Edit] Link to Post, for clarity.


Awesome, I’ll keep an eye on that thread.