IMP does not go "online" after a power outage

I am running imp on 3.7V LiPo battery. Last night I saw the power on pin9 go down to 2.7 volts. Then noticed Device was “offline” in Planner. The battery drained. I am using Solar to charge it, so overnight was not going to charge.

But this morning, after 5+ hours of good sunshine, I see the Solar panel is charging the battery just fine.

The battery is still connected to IMP. IMP had “red” light on and it was “offline.” The application for the IMP is for use outside and having it come back online by itself after say 8-hours or even 2-days of no power is what I am after.

Behavior I was expecting on the IMP was that when power was back up, it would turn on again. Am I correct to assume that?

Note: The way I got it back online was to unseat/reseat the IMP.


It sounds like something in your charging circuit might be locking out power once the voltage goes below a certain threshold. What are you using as a charging circuit/chip?

hmm. k I am using:

Good circuit because it uses solar direct, and charges too. Without solar, uses battery. But IMP’s light was “off” when it was online last night when there was some juice left in the battery. This morning the indicator on IMP was red. Does it not mean at least the source voltage was good?

I can try another thing with an LED that goes off/on to see if circuit cuts out and in and what happens to LED.

When you say the Imp red light was on, do you mean it was blinking? The Blinkup lights will normally only be on for 60 seconds after a boot, however, if the Imp is boot looping because your battery voltage is too low it will likely blink red continuously. You want to make sure there is under voltage protection somewhere in your circuit to avoid this. You also want the circuit to not power back up until your battery has enough capacity to fully bring the Imp and your circuit online. I’d say one of these isn’t functioning properly.

I recommend reading through the material on LiPo battery solutions in the documentation… it will make all of this much more clear.

I am hoping to make a Imp module with a good solar/energy harvesting set up soon. Its complex but really cool.

The RED light was solid (not blinking). I am going to read through the Adafruit solar charger to see about the cut-off and turn-back-on states.

Yes the solar/battery would be great - so few to chose from surprisingly,

Ideally you should have an undervoltage lockout for this to ensure the imp gets cut off before it would operate erratically, and power wouldn’t be restored until it was above a safe level.

If you look at the nora reference design, you’ll see an example of such a circuit. You’d need to use the right version of the controller IC to give the right thresholds for your battery though.

Hi Hugo et al

Thanks for referring to Nora I will look. Was hoping to use the circuit I’ve already purchased from Adafruit which uses Microchip and it should have this undervoltage lockout/restore (seems a must for such an IC).

But - let me ask this. This issue happened again. Specifically, the RED stays solid. This is not explainable - I looked over the BlinkUp troubleshooting color chart, and a solid RED is not on their list.

Have I found a bug? How do I get some answer on it from Electric Imp team - so I know I am not chasing something elsewhere that’s not going to pan out bcoz its a possible bug on IMP?

As I said, this is erratic behavior due to low voltage most likely. The imp is not successfully running any code (so it can’t indicate anything that would match a blinkup code). It likely ran enough code to turn the led on, and then the CPU got into a strange state due to the brownout, and the CPU locked up. I don’t believe this is a bug, because software doesn’t have control if the CPU goes haywire. There is auto-reset hardware in the SoC for brownouts but it’s hard to tell whether this would help in your case without having it on our bench to analyze.

We’ve not seen this state ourselves, despite running similar setups (running the imp from a supercap and a solar cell), but I can believe it could exist.