SDS011 dust sensor reading

sds011

#!/usr/bin/python
# coding=utf-8
# "DATASHEET": http://cl.ly/ekot
from __future__ import print_function
import serial, struct, sys, time

DEBUG = 1
CMD_MODE = 2
CMD_QUERY_DATA = 4
CMD_DEVICE_ID = 5
CMD_SLEEP = 6
CMD_FIRMWARE = 7
CMD_WORKING_PERIOD = 8
MODE_ACTIVE = 0
MODE_QUERY = 1

ser = serial.Serial()
ser.port = sys.argv[1]
ser.baudrate = 9600

ser.open()
ser.flushInput()

byte, data = 0, ""

def dump(d, prefix=''):
    print(prefix + ' '.join(x.encode('hex') for x in d))

def construct_command(cmd, data=[]):
    assert len(data) <= 12
    data += [0,]*(12-len(data))
    checksum = (sum(data)+cmd-2)%256
    ret = "\xaa\xb4" + chr(cmd)
    ret += ''.join(chr(x) for x in data)
    ret += "\xff\xff" + chr(checksum) + "\xab"

    if DEBUG:
        dump(ret, '> ')
    return ret

def process_data(d):
    r = struct.unpack('<HHxxBB', d[2:])
    pm25 = r[0]/10.0
    pm10 = r[1]/10.0
    checksum = sum(ord(v) for v in d[2:8])%256
    print("PM 2.5: {} μg/m^3  PM 10: {} μg/m^3 CRC={}".format(pm25, pm10, "OK" if (checksum==r[2] and r[3]==0xab) else "NOK"))

def process_version(d):
    r = struct.unpack('<BBBHBB', d[3:])
    checksum = sum(ord(v) for v in d[2:8])%256
    print("Y: {}, M: {}, D: {}, ID: {}, CRC={}".format(r[0], r[1], r[2], hex(r[3]), "OK" if (checksum==r[4] and r[5]==0xab) else "NOK"))

def read_response():
    byte = 0
    while byte != "\xaa":
        byte = ser.read(size=1)

    d = ser.read(size=9)

    if DEBUG:
        dump(d, '< ')
    return byte + d

def cmd_set_mode(mode=MODE_QUERY):
    ser.write(construct_command(CMD_MODE, [0x1, mode]))
    read_response()

def cmd_query_data():
    ser.write(construct_command(CMD_QUERY_DATA))
    d = read_response()
    if d[1] == "\xc0":
        process_data(d)

def cmd_set_sleep(sleep=1):
    mode = 0 if sleep else 1
    ser.write(construct_command(CMD_SLEEP, [0x1, mode]))
    read_response()

def cmd_set_working_period(period):
    ser.write(construct_command(CMD_WORKING_PERIOD, [0x1, period]))
    read_response()

def cmd_firmware_ver():
    ser.write(construct_command(CMD_FIRMWARE))
    d = read_response()
    process_version(d)

def cmd_set_id(id):
    id_h = (id>>8) % 256
    id_l = id % 256
    ser.write(construct_command(CMD_DEVICE_ID, [0]*10+[id_l, id_h]))
    read_response()

if __name__ == "__main__":
    cmd_set_sleep(0)
    cmd_set_mode(1);
    cmd_firmware_ver()
    time.sleep(3)

    cmd_query_data();
    cmd_set_mode(0);
    cmd_set_sleep()

Thanks for the supports, after more hours of Googling and much trial&error I found out I am not the only one who ran into this issue. For who is interested, this topic summarizes it best: https://www.raspberrypi.org/forums/viewtopic.php?t=219026

Other posts on this topic:

• https://www.raspberrypi.org/forums/viewtopic.php?t=274549
• https://www.raspberrypi.org/forums/viewtopic.php?t=237119

The only option to make it somewhat more compact is to replace the USB > UART board with a angled micro USB so it doesn't stick out that much.

One last hope I have is to pick up power from the USB port to see if that doesn't reboot it, trying that later today. Setting the SDS011 to sleep and waking it up again does work via that USB dongle, so let's see what happens if you draw power from there instead of the GPIO pins directly ;-)
Cheers,
Remco

OK, not sure if it's the 'correct' way to go, but I did get it working withouth that stupid dongle. Wiring needs some TLC, but it's working now. I can put the sensor to sleep and wake it up again without my RPI rebooting. Complete lenghty lengthy write-up with more pics on https://tinker.rembrand.nl/2021/01/02/using-sds011-via-uart/

I combined it with a DHT22 sensor for now and it's happily recording every 5 minutes:

Cheers,
Remco

@remco have you tried.putting a capacitor between the 5v and gnd to smooth out the voltage drop?

Wouldn't even know which value to pick; my knowledge of electronics is limited to none ;-) I did read on several posts/boards that others did try that, including circuits with diodes and all, but to no avail. Best I can do is logic and this seems to work as expected. Until I find some other solution, I'll tidy this up and move it to an enclosure outside to do further testing with the scripts I am working on. I want to collect the data to a database, do some graphs, send it properly formated to luftdaten. All knowledge gaps so I have quite some challenges. Your scripts helped me to get started with the SDS011 though, so many thanks for that :-)
Remco

Wicked, also check the /var/log/syslog file or dmesg, i remember low voltage warnings in one of them when I was doing too much with my weak 5v supply

Wicked, also check the /var/log/syslog file or dmesg, i remember low voltage warnings in one of them when I was doing too much with my weak 5v supply

It's been running in the backyard since yesterday evening, 0 hits on 'voltage' issues it seems. Ever since then it has measured 10 times with 1 second intervals, put the SDS011 to sleep for about 5 minutes, wake up and measure again. So I am still optimistic this works ;-)
Pics of the enclosure you can find here. Currently using a standard weatherproof junction box which was always my entention for the outdoor enclosure.
Remco

What needs to change in the code if I would not use Sensor Hat?

@alokvermaiitr what you mean by Sensor Hat?

For those still having the issue where it maxes out, I wrote some new code which seems to work past the 20,000 mark https://github.com/FaisalAhmed123/Nova-PM2.5-Sensor-Reading-Interpreter/blob/main/main.py