#!/usr/bin/env python
# pi_power.py
# Robert Jones 2016 jones@craic.com
# The code for reading the MCP3008 analog to digital convertor (readadc) was
# written by Limor "Ladyada" Fried for Adafruit Industries, (c) 2015
# This code is released into the public domain
# Works with an Adafruit PowerBoost 1000C LiPo battery charger
# Writes the fraction of battery remaining as well as the current power source to the file /home/pi/.pi_power
# format: <float 0.00 - 1.00>,<string [battery|usb]>
# 0.75,battery
# 1.00,usb
import time
import os
import argparse
import RPi.GPIO as GPIO
# read SPI data from MCP3008 chip, 8 possible adc's (0 thru 7)
def readadc(adcnum, clockpin, mosipin, misopin, cspin):
if ((adcnum > 7) or (adcnum < 0)):
return -1
GPIO.output(cspin, True)
GPIO.output(clockpin, False) # start clock low
GPIO.output(cspin, False) # bring CS low
commandout = adcnum
commandout |= 0x18 # start bit + single-ended bit
commandout <<= 3 # we only need to send 5 bits here
for i in range(5):
if (commandout & 0x80):
GPIO.output(mosipin, True)
else:
GPIO.output(mosipin, False)
commandout <<= 1
GPIO.output(clockpin, True)
GPIO.output(clockpin, False)
adcout = 0
# read in one empty bit, one null bit and 10 ADC bits
for i in range(12):
GPIO.output(clockpin, True)
GPIO.output(clockpin, False)
adcout <<= 1
if (GPIO.input(misopin)):
adcout |= 0x1
GPIO.output(cspin, True)
adcout >>= 1 # first bit is 'null' so drop it
return adcout
# Calculate the output of a voltage divider
# voltage_divider layout is:
# Vin ---[ R1 ]---[ R2 ]---GND
# |
# Vout
#
# Vout = R2 / (R1 + R2) * Vin
# e.g. if R1 = 6800 and R2 = 10000 and Vin is 5.2V then Vout is 3.095
#
def voltage_divider(r1, r2, vin):
vout = vin * (r2 / (r1 + r2))
return vout
# Set up a trigger to shutdown the system when the power button is pressed
# define a setup routine and the actual shutdown method
# The shutdown code is based on that in https://github.com/NeonHorizon/lipopi
def user_shutdown_setup(shutdown_pin):
# setup the pin to check the shutdown switch - use the internal pull down resistor
GPIO.setup(shutdown_pin, GPIO.IN, pull_up_down=GPIO.PUD_DOWN)
# create a trigger for the shutdown switch
GPIO.add_event_detect(shutdown_pin, GPIO.RISING, callback=user_shutdown, bouncetime=1000)
# User has pressed shutdown button - initiate a clean shutdown
def user_shutdown(channel):
global safe_mode
shutdown_delay = 10 # seconds
# in Safe Mode, wait 2 mins before actually shutting down
if(safe_mode):
cmd = "sudo wall 'System shutting down in 2 minutes - SAFE MODE'"
os.system(cmd)
time.sleep(120)
cmd = "sudo wall 'System shutting down in %d seconds'" % shutdown_delay
os.system(cmd)
time.sleep(shutdown_delay)
# Log message is added to /var/log/messages
os.system("sudo logger -t 'pi_power' '** User initiated shut down **'")
GPIO.cleanup()
os.system("sudo shutdown now")
# Shutdown system because of low battery
def low_battery_shutdown():
global safe_mode
shutdown_delay = 30 # seconds
# in Safe Mode, wait 2 mins before actually shutting down
if(safe_mode):
cmd = "sudo wall 'System shutting down in 2 minutes - SAFE MODE'"
os.system(cmd)
time.sleep(120)
cmd = "sudo wall 'System shutting down in %d seconds'" % shutdown_delay
os.system(cmd)
time.sleep(shutdown_delay)
# Log message is added to /var/log/messages
os.system("sudo logger -t 'pi_power' '** Low Battery - shutting down now **'")
GPIO.cleanup()
os.system("sudo shutdown now")
# MAIN -----------------------
GPIO.setwarnings(False)
GPIO.setmode(GPIO.BCM)
# Command Line Arguments
# --log write time, voltage, etc to a log file
# --debug write time, voltage, etc to STDOUT
parser = argparse.ArgumentParser(description='Pi Power - Monitor battery status on RasPi projects powered via Adafruit PowerBoost 1000C')
parser.add_argument('-d', '--debug', action='store_true')
parser.add_argument('-l', '--log', action='store_true')
parser.add_argument('-s', '--safe', action='store_true')
args = parser.parse_args()
safe_mode = False
if(args.safe):
safe_mode = True
# Setup the GPIO pin to use with the use shutdown button
user_shutdown_pin = 26
user_shutdown_setup(user_shutdown_pin)
# Setup the connection to the ADC
# specify the Raspberry Pi GPIO pins to be used to connect to the SPI interface on the MCP3008 ADC
SPICLK = 18
SPIMISO = 23
SPIMOSI = 24
SPICS = 25
# set up the SPI interface pins
GPIO.setup(SPIMOSI, GPIO.OUT)
GPIO.setup(SPIMISO, GPIO.IN)
GPIO.setup(SPICLK, GPIO.OUT)
GPIO.setup(SPICS, GPIO.OUT)
# Vbat to adc #0, Vusb connected to #1
v_bat_adc_pin = 0
v_usb_adc_pin = 1
# Voltage divider drops the PowerBoost voltage from around 5V to under 3.3V which is the limit for the Pi
voltage_divider_r1 = 6800.0
voltage_divider_r2 = 10000.0
# Define the min and max voltage ranges for the inputs
usb_min_voltage = 0.0
usb_max_voltage = 5.2
gpio_min_voltage = 0.0
gpio_max_voltage = 3.3
# LiPo battery voltage range - actual range is 3.7V to 4.2V
# But in practice the measured range is reduced as Vbat always drops from 4.2 to around 4.05 when the
# USB cable is removed - so this is the effective range:
battery_min_voltage = 3.75
battery_max_voltage = 4.05
# this is the effective max voltage, prior to the divider, that the ADC can register
adc_conversion_factor = (gpio_max_voltage / voltage_divider(voltage_divider_r1, voltage_divider_r2, usb_max_voltage)) * usb_max_voltage
pi_power_status_path = '/home/pi/.pi_power_status'
pi_power_log_path = '/home/pi/pi_power_log.csv'
# initialize an empty log file
if(args.log):
with open(pi_power_log_path, "w") as f:
f.write('Time,Vbat,Vusb,Frac,Source\n')
# Take a measurement every poll_interval * seconds * - default 60
poll_interval = 60
power_source = ''
power_source_previous = ''
fraction_battery = 1.0
# Define the minimum battery level at which shutdown is triggered
fraction_battery_min = 0.075
if(args.debug):
print 'Time Vbat Vusb Frac Source'
elapsed_time = 0
msg = ''
while True:
# read the analog pins on the ACD (range 0-1023) and convert to 0.0-1.0
frac_v_bat = round(readadc(v_bat_adc_pin, SPICLK, SPIMOSI, SPIMISO, SPICS)) / 1023.0
frac_v_usb = round(readadc(v_usb_adc_pin, SPICLK, SPIMOSI, SPIMISO, SPICS)) / 1023.0
# Calculate the true voltage
v_bat = frac_v_bat * adc_conversion_factor
v_usb = frac_v_usb * adc_conversion_factor
fraction_battery = (v_bat - battery_min_voltage) / (battery_max_voltage - battery_min_voltage)
if fraction_battery > 1.0:
fraction_battery = 1.0
elif fraction_battery < 0.0:
fraction_battery = 0.0
# is the USB cable connected ? Vusb is either 0.0 or around 5.2V
if v_usb > 1.0:
power_source = 'usb'
else:
power_source = 'battery'
if power_source == 'usb' and power_source_previous == 'battery':
print '** USB cable connected'
elif power_source == 'battery' and power_source_previous == 'usb':
print '** USB cable disconnected'
power_source_previous = power_source
msg = ''
# If battery is too low then shutdown
if fraction_battery < fraction_battery_min:
msg = 'Low Battery - shutdown now'
if(args.debug):
print "** LOW BATTERY - shutting down........"
# shutdown after writing to the log file
if(args.debug):
print '{0:6d} {1:.3f} {2:.3f} {3:.3f} {4:s} {5:s}'.format(elapsed_time, v_bat, v_usb, fraction_battery, power_source, msg)
# Open log file, write one line and close
# This handles the case where the battery is allowed to drain completely and
# shutdown in which case the file may be corrupted
if(args.log):
with open(pi_power_log_path, "a") as f:
f.write('{0:d},{1:.3f},{2:.3f},{3:.3f},{4:s},{5:s}\n'.format(elapsed_time, v_bat, v_usb, fraction_battery, power_source, msg))
# Write the .pi_power status file - used by pi_power_leds.py
with open(pi_power_status_path, "w") as f:
f.write('{0:.3f},{1:s}\n'.format(fraction_battery,power_source))
# Low battery shutdown - specify the time delay in seconds
if fraction_battery < fraction_battery_min:
low_battery_shutdown()
# sleep poll_interval seconds between updates
time.sleep(poll_interval)
elapsed_time += poll_interval
