vsys.py

"""
# vsys.py : Read Pico Vsys voltage using ADC channel 3 (GPIO 29)
# takes parameters ADC Vref and Voffset (ideally would be 3.3,0)
# NOTE: ONLY for pico board, does not work as intended on pico-W 
# for details see forums.raspberrypi.com/viewtopic.php?t=340919
# J.Beale 4-Dec-2022

# Usage Example:
import vsys
from time import sleep, time

vs = vsys.Vsys(3.24,0.02) # to read Pico Vsys voltage
while True:
    volts = vs.read()
    print(volts)
    sleep(1)
"""

from machine import Pin, ADC

class Vsys:
    def __init__(self, vref=3.234, voff=0.027):
        self.vOffset = voff    # individually measured offset
        self.Vref = vref       # individually measured value of ADC Vref
        Pin(29, Pin.IN)        # no pullup/down for pin 29 reading Vsys
        self.vsysCh = ADC(3)   # connects to Vsys
        self.ADCmax = 65535    # max reported by ADC().read_u16
        self.Rratio = 3.0      # Pico 3:1 onboard Vsys divider
        self.vScale = self.Rratio * self.Vref / self.ADCmax

    def read(self):  # read vSys in volts
        return (self.vsysCh.read_u16() * self.vScale + self.vOffset)