Power Shield

The Power Shield library provides functions to use the on-board MAX17043 fuel guage via I2C

Typical usage

Connect a Photon to a Power Shield with a 3.7V LiPo battery and use the library to get the voltage and state of charge.

#include "PowerShield.h"

PowerShield batteryMonitor;

void setup() {
    batteryMonitor.begin(); 
    batteryMonitor.quickStart();
}
  
void loop() {
    delay(5000);

    float cellVoltage = batteryMonitor.getVCell();
    float stateOfCharge = batteryMonitor.getSoC();

    Particle.publish("voltage", String(cellVoltage));
    Particle.publish("soc", String(stateOfCharge));
}

Examples

See complete example in the examples directory.

1. Read voltage over serial: In this example the Particle device sends the volatge and SoC readings over serial every 1 second
2. Publish voltage readings: In this example the Particle device publishes the voltage and SoC readings every 10 minutes and stays in deep sleep mode for the rest of the time
3. Interrupt on low battery: In this example the Particle device publishes an event when the battery state of charge becomes low.

Reference

PowerShield

PowerShield batteryMonitor;

Creates an object to interact with the MAX17043 fuel gauge on the Power Shield.

begin

batteryMonitor.begin();

Starts communicating with the fuel gauge. Should normally be called once in setup.

quickStart

batteryMonitor.quickstart();

Resume state of charge calculations. See Quick-Start in the MAX17043 datasheet for details.

getVCell

float cellVoltage = batteryMonitor.getVCell();

Reads the voltage of the single cell battery connected to the Power Shield. The range is 0 V to 5 V.

getSoC

float stateOfCharge = batteryMonitor.getSoC();

Reads the state of charge of the single cell battery connected to the Power Shield, from 0% to 100%, so that you know when to send out an alert to replace/charge the battery.

getVersion

int version = batteryMonitor.getVersion();

The version of the MAX17043 chip, currently 3.

getCompensateValue

Gets the configuration for battery chemistry. See CONFIG in the MAX17043 datasheet for details.

getAlertThreshold

byte thereshold = batteryMonitor.getAlertThreshold();

Gets the state of charge threshold (1 to 32%) that will generate a low pulse on pin D3 when the state of charge falls below this level.

The default threshold is 4%.

For the pulse to be generated the ALRT solder bridge needs to be closed on the Power Shield.

To trigger an interrupt on low battery, configure pin D3 for a falling interrupt. See the interrupt on low voltage example for details.

setAlertThreshold

batteryMonitor.setAlertThreshold(threshold);

Sets the state of charge threshold (1 to 32%) that will generate a pulse on D3.

getAlert

bool lowBatteryAlert = batteryMonitor.getAlert();

Returns true when the state of charge is below the alert threshold. Use this if you don't want to use the D3 pin as an low battery interrupt.

Once true, this will stay true, even if the battery is charged, until cleared by software with clearAlert().

clearAlert

batteryMonitor.clearAlert();

Clears the low voltage alert so that getAlert() returns false.

reset

batteryMonitor.reset();

Reset the MAX17043 fuel gauge as if power had been removed.

Resource Utilization

The Power Shield uses pins D0, D1 (I2C) and D3 (if optional solder bridge is closed).

References

• Power Shield Documentation
• MAX17043 datasheet

License

Copyright 2015 Particle

Released under the LGPL license