Just some micropython code to talk to a HPM sensor. Just work in progress

mstack_hpmhack.py

from m5stack import *
from m5ui import *
from machine import UART
import time
import struct

# This is the only UART that works. 
uart2 = UART(1, tx=17, rx=16)
uart2.init(9600)
while True:
    # Making data display more reasonable
    time.sleep_ms(750)
    lcd.clear()
    # The command to start measurement
    # source https://sensing.honeywell.com/honeywell-sensing-hpm-series-particle-sensors-datasheet-32322550-e-en.pdf
    # Page 5
    uart2.write('\x68\x01\x01\x96')
    data=uart2.read(32)
    # Opps there is problem, 
    # call the command to stop measurement every time there is problem
    if not data:
        lcd.print("No data", 20, 20)
        uart2.write('\x68\x01\x02\x95')
        continue
    # Should only have 32 bit of data
    if len(data) != 32:
        lcd.print("Bad data", 20, 20)
        lcd.print(data, 20, 30)
        uart2.write('\x68\x01\x02\x95')
        continue
    # measurement must start with 0x42
    if data[0] != 0x42:
        lcd.print("Bad data", 20, 20)
        lcd.print(data, 20, 30)
        uart2.write('\x68\x01\x02\x95')
        continue
    l = list(data)
    # The number is big endian. Also drop the first 4 byte
    # Covert the rest into 14 number
    frame = struct.unpack(">HHHHHHHHHHHHHH", bytes(l[4:]))
    # I really only care about frame[1] and frame[2]. WHich is PM2.5 and PM10
    # Source https://sensing.honeywell.com/honeywell-sensing-hpm-series-particle-sensors-datasheet-32322550-e-en.pdf
    # Page 6
    output = "PM 2.5 = {pm25}".format(pm25=frame[1])
    lcd.print(output, 20, 30)
    uart2.write('\x68\x01\x02\x95')