Measuring the Battery on Argon

I am using an Argon, and I understand there is no fuel gauge chip:

"The Argon device does not have a fuel gauge chip, however you can determine the voltage of the LiPo battery, if present."

I therefore have two (2) questions:

  1. The documentation states that I can measure the battery voltage by:

float voltage = analogRead(BATT) * 0.0011224;

which seems to be providing a reasonable number (4.11 with fully charged batteries). My question is, at what point should I consider the voltage drop too low to continue, and must charge the device? 3.8V? 3.6V? 3.0V? Any recommendations?

  1. The documentation also states that the charge indicator on the Argon can be read using:

bool charging = !digitalRead(CHG);

"In other words, the CHG input is 0 when charging and 1 when not charging, and the ! inverts this logic to make it easier to use."

However, using the following code:

if (!digitalRead(CHG)) {
    Particle.publish("Battery", "Charging");
} else {
    Particle.publish("Battery", "Not Charging");

it always says "Charging", even when there is nothing plugged in at the USB. So what am I doing wrong?

Note: I am using 2x Lithium-Ion (18650) batteries in parallel, so not LiPo, but the electrical characteristics appear to be the same, and I wouldn't guess that a different battery chemistry should affect whether or not the Argon thinks its charging when there is nothing plugged in to the USB.


Dave Filip

3.6V would be a conservative lower limit leaving some margin for low temperatures and/or measuring errors.
3.4V if you want to stretch it.
You should not go below 3.2V.

About the CHG input...

you need to consider the PWR input, also, to determine charging. Here is a thread with a solution by @ScruffR about a similar question:

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Regarding the voltages, thanks, I'll uses those as guidelines, and confirm with some testing around them, but that sounds reasonable. I just needed a starting point of reference, and this is helpful.

Regarding the 'Charging', I think I was misinterpreting the meaning, and now understand that it has to be taken In context of running on USB power or running on battery power.

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The Argon charger IC is not designed to handle two batteries in parallel so your configuration is not recommended. You could use a larger capacity single LiPo battery instead.

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