| Date: | 2018-04-28 |
|---|---|
| tags: | PMS5003, Python 3, FT232H |
| Author: | Roland Smith |
The dust-monitor.py program allows you to read and log particulate matter
(“PM”) data from the plantower PMS5003 sensor on computer. I bought mine from
a local Adafruit reseller.
The PMS5003 outputs data over a serial connection. I've used an FT232H serial ↔ USB bridge to connect it to my PC.
Except from the hardware, this program uses the pyftdi module to connect to
the FT232H device. This module in turn requires pyserial and pyusb. The
advantage of pyftdi is that it is a pure python solution and support
serial tty, SPI and I²C connections. It does not require native libraries which
makes installing it easier.
Note that for this to work, any native driver for FTDI chips needs to be
unloaded. On FreeBSD this is accomplished by commenting out the nomatch
statement in /etc/devd/usb.conf that loads uftdi driver and restarting
devd.
If you do not want to use pyftdi, check out the native branch. That branch
uses the native driver.
This program has been written for Python 3 on the FreeBSD operating system version 11.1. I expect it will work on other POSIX systems, and maybe even on ms-windows. But I haven't tested that.
To use the sensor I had to read the manual but also look at e.g. the adafruit sample code because some points were not completely clear to me from the documentation. In the process I made some annotations in the manual. Since there don't seem to be restrictions to modifications and redistribution of that manual, I've made my annotated version available.
The dust-monitor.py program is designed to be started from the command
line, where it should probably be started so as to run in the background. The
main options are:
-por--portSelect the serial port to use. Defaults to/dev/cuaU0. Note that the user running this program should have read/write access to this port.-ior--intervalSets the interval between measurements. Defaults to 5 s, which is also the minimum interval.
There is one required argument, which is a filename template. This template
should contain one {}-pair, which will be replaced by the full ISO-8601
notation of the UTC date and time when the program was started. This serves to make
the filenames unique and as a reminder.
An example:
./dust-monitor.py -p ftdi://ftdi:232h/2 -i 900 '/tmp/pmdata-{}.txt'The program would open the ftdi://ftdi:232h/2 device (the second FT232H
connected to the system) to read data every fifteen minutes. The data would be
written to /tmp/pmdata-2018-04-14T21:39:59Z.txt, where the datetime is
just an example.
The data is stored as plain text so that is is readable by both humans and
computers. Apart from a header (lines starting with #), the data looks
like this:
2018-04-13T15:21:54Z 11 14 17 2154 604 82 4 4 2
Each line is a single data point. The columns are separated by spaces. Apart from the first column, all columns are unsigned integers. The meaning of the columns is:
- UTC date and time in ISO-8601 format
- PM 1.0 in μg/m³ [i.e particles ≤ 1 μm]
- PM 2.5 in μg/m³ [particles ≤ 2.5 μm]
- PM 10 in μg/m³ [particles ≤ 10 μm]
- number of particles >0.3 μm / 0.1 dm³ of air
- number of particles >0.5 μm / 0.1 dm³ of air
- number of particles >1.0 μm / 0.1 dm³ of air
- number of particles >2.5 μm / 0.1 dm³ of air
- number of particles >5 μm / 0.1 dm³ of air
- number of particles >10 μm / 0.1 dm³ of air
Many programs could be used to load and analyze/manipulate this data. Below is an example how to read the data in Python with numpy.
import numpy as np
columns = np.genfromtxt('/tmp/pmdata-2018-04-14T21:39:59Z.txt',
comments="#", delimiter=" ",
usecols=tuple(range(1, 10))).T
# Every of these columns pmX is particulate matter < X/10 μm in μg/m³.
pm10 = columns[0]
pm25 = columns[1]
pm100 = columns[2]
# Every of these columns partN is a count of particles > N/10 μm in 0.1 dm³ or air.
part03 = columns[3]
part05 = columns[4]
part10 = columns[5]
part25 = columns[6]
part50 = columns[7]
part100 = columns[8]