Script that controls an external circuit to keep the laptops battery voltage within nominal voltage. The DTR signal is used to control the circuit.

charge_control.py

#/sys/bus/acpi/drivers/battery/PNP0C0A:00/power_supply/BAT0
#See https://i.imgur.com/yuVyiW7.png for picture of the böp this controls
import sys, serial, time

min_voltage = 3.5
max_voltage = 3.8
interval = 300			#Every 5 minutes

def read_num(filename):
	with open(filename, 'r') as infile:
		return float(infile.__next__())

def get_voltage(max_voltage=4.20):
	return max_voltage * read_num('energy_now') / read_num('energy_full')


def control_loop():
	current_state = None	#Unknown
	s = serial.Serial('/dev/ttyUSB0')

	try:
		while True:
			v = get_voltage()
			print(time.ctime(), 'MEASURE', v, file=sys.stderr)
			if v < min_voltage:
				if current_state is None or current_state == False:
					print(time.ctime(), 'ON', file=sys.stderr, flush=True)
					s.setDTR(False)
					current_state = True

			elif v > max_voltage:
				if current_state is None or current_state == True:
					print(time.ctime(), 'OFF',file=sys.stderr, flush=True)	
					s.setDTR(True)
					current_state = False

			time.sleep(interval)
	
	except KeyboardInterrupt:
		s.close()
		return	

if __name__ == '__main__':
	print(time.ctime(), 'START', file=sys.stderr, flush=True)
	control_loop()
	print(time.ctime(), 'STOP', file=sys.stderr, flush=True)