95 lines
3.2 KiB
Python
95 lines
3.2 KiB
Python
# SPDX-License-Identifier: LGPL-3.0-or-later
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# Copyright (C) 2020 Daniel Thompson
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"""Generic lithium ion battery driver
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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"""
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import micropython
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# don't remove Pin import even though your IDE tells you it's unused, otherwise
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# micropython can't load your battery level.
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from machine import Pin, ADC
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import array
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class Battery(object):
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"""Generic lithium ion battery driver.
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.. automethod:: __init__
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"""
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def __init__(self, battery, charging, power=None):
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"""Specify the pins used to provide battery status.
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:param Pin battery: The ADC-capable pin that can be used to measure
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battery voltage.
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:param Pin charging: A pin (or Signal) that reports the charger status.
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:param Pin power: A pin (or Signal) that reports whether the device
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has external power, defaults to None (which means
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use the charging pin for power reporting too).
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"""
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self._battery = ADC(battery)
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self._charging = charging
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self._power = power
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self._cache = array.array("I")
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@micropython.native
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def charging(self):
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"""Get the charging state of the battery.
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:returns: True if the battery is charging, False otherwise.
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"""
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return self._charging.value()
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def power(self):
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"""Check whether the device has external power.
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:returns: True if the device has an external power source, False
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otherwise.
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"""
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if self._power:
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return self._power.value()
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return self._charging.value()
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def voltage_mv(self):
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"""Read the battery voltage.
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Assumes a 50/50 voltage divider and a 3.3v power supply
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The last values is kept in a cache and only the minium cached value is
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shown to the user, this is to avoid the battery level
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going up and down because of the lack of precision of the mv.
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Note that this will underestimate battery level.
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:returns: Battery voltage, in millivolts.
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"""
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raw = self._battery.read_u16()
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mv = (2 * 3300 * raw) // 65535
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cache = self._cache
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if self._charging.value(): # if charging, reset cache
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if len(cache):
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cache = array.array("I")
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return mv
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if len(cache) < 2:
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cache.append(mv)
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return mv
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if len(cache) > 2: # should not happen
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cache = cache[-2:]
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if mv != cache[0] and mv != cache[1]:
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cache[0] = cache[1]
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cache[1] = mv
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return sum(cache) / 2
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def level(self):
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"""Estimate the battery level.
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The current the estimation approach is extremely simple. It is assumes
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the discharge from 4v to 3.5v is roughly linear and 4v is 100% and
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that 3.5v is 5%. Below 3.5v the voltage will start to drop pretty
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sharply so we will drop from 5% to 0% pretty fast... but we'll
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live with that for now.
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:returns: Estimate battery level in percent.
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"""
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mv = self.voltage_mv()
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level = int((mv - 3500) / (700) * 100) # 0.7V is 4.2-3.5V
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return min(100, max(0, level))
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