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# SPDX-License-Identifier: LGPL-3.0-or-later
# Copyright (C) 2020 Daniel Thompson
"""Generic lithium ion battery driver
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
"""
import micropython
from machine import Pin, ADC
class Battery(object):
"""Generic lithium ion battery driver.
.. automethod:: __init__
"""
def __init__(self, battery, charging, power=None):
"""Specify the pins used to provide battery status.
:param Pin battery: The ADC-capable pin that can be used to measure
battery voltage.
:param Pin charging: A pin (or Signal) that reports the charger status.
:param Pin power: A pin (or Signal) that reports whether the device
has external power, defaults to None (which means
use the charging pin for power reporting too).
"""
self._battery = ADC(battery)
self._charging = charging
self._power = power
@micropython.native
def charging(self):
"""Get the charging state of the battery.
:returns: True if the battery is charging, False otherwise.
"""
return self._charging.value()
def power(self):
"""Check whether the device has external power.
:returns: True if the device has an external power source, False
otherwise.
"""
if self._power:
return self._power.value()
return self._charging.value()
def voltage_mv(self):
"""Read the battery voltage.
Assumes a 50/50 voltage divider and a 3.3v power supply
:returns: Battery voltage, in millivolts.
"""
raw = self._battery.read_u16()
return (2 * 3300 * raw) // 65535
def level(self):
"""Estimate the battery level.
The current the estimation approach is extremely simple. It is assumes
the discharge from 4v to 3.5v is roughly linear and 4v is 100% and
that 3.5v is 5%. Below 3.5v the voltage will start to drop pretty
sharply to we will drop from 5% to 0% pretty fast... but we'll
live with that for now.
:returns: Estimate battery level in percent.
"""
mv = self.voltage_mv()
level = ((19 * mv) // 100) - 660
if level > 100:
return 100
if level < 0:
return 0
return level
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