GCARE OPC-N3 Monitor

Stable Release

Idris Hayward (CaderIdrisGH@outlook.com)

COPYRIGHT 2021, Global Centre for Clean Air Research, The University of Surrey

GNU General Public License v3.0

This program has been designed to be run on a Raspberry Pi running Ubuntu 20.04 LTS desktop 64 bit with an 800x640 touchscreen display. It is likely to run on other distributions and devices though some modifications may be required.

Adapted from Python2 code written by Daniel Jarvis and licensed under GPL v3.0: https://github.com/JarvisSan22/OPC-N3_python

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Table of Contents

1. Standard Operating Procedure
2. Settings
3. Setup
4. API
5. Components

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Standard Operating Procedure

Step 1: Run program

The GCARE-OPCN3 program can be run in one of three ways

Option A: Shortcut

If the GCARE-extras.sh script was run during setup, an executable shortcut should be present on the desktop. Double click this to run the program.

Option B: Autorun

If the GCARE-extras.sh script was run during setup, the program will automatically initialise 20 seconds after login.

Option C: Terminal

The program can also be initialised via the terminal.

1. cd ~/Documents/GCARE-OPCN3 (or whichever directory the repository has been saved in)
2. bash run.sh or ./run.sh

Once the program is initialised via either method, the opening blurb should show, indicating some of the parameters used.

The first block shows the author information for the program, including current version number and status.

The second block shows where the data is being saved to. If no external devices are present like in this example, data is saved to the user's Documents folder in the OPC Data directory.

The third block indicates whether a connection to the device has been made. If it has not, the user may not have been properly added to the dialout group while running setup.sh or the device may be connected to a different port to the one specified in OPCSettings.json.

The fourth block is the text output of the program testing the connection. You should be able to hear the fan being disabled and re-enabled. If you cannot, there may be an issue with the connection.

The fifth block indicates that the device is now recording measurements and informs the user on how and when to exit the program.

The sixth block indicates the time the measurement program started and when the first measurement will take place. More information on this can be found in Settings.

While measuring, the program displays the latest measurement at the bottom of the terminal.

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Settings

Key	Type	Description	Options
Name	str	Name of the device	Any str
Port	str	Path to the device	Path to the OPC-N3 USB adapter in the /dev/ directory
Measurement Time	str	Measurement frequency	Options below
Use Bin Data	bool	Record bin data	true/false
Fan Speed	int	Unused	int between 0-128
File Path	str	Path to save data to	Any valid path, leave empty to automatically select path with find_valid_path

Options for Measurement Time

Argument	Interval
1m	1 minute
5m	5 minutes
10m	10 minutes
15m	15 minutes
30m	30 minutes
1h	1 hours

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Setup

This setup section is assuming the program is to be run on Ubuntu 20.04 LTS for Raspberry Pi. Other distributions and devices may vary.

Step 1: Power on device

Step 2: Ensure latest updates are installed

Ensure all packages on the device are up to date. Open the terminal via CTRL + ALT + T or via the home menu in the bottom left of the screen.

Enter sudo apt update to check whether any packages require updating. Enter the password when prompted.

If any packages need to be upgraded, enter sudo apt upgrade

Step 3: Download Program from GitHub

There are two ways to download the latest program from Github.

Option A: Download code from repository directly

Visit the repository at https://github.com/Joppleganger/GCARE-OPCN3 and open the green download menu located at the right side of the screen. Click download ZIP file to download an archive of the latest code which can then be extracted to a directory of your choice.

Option B: Clone repository via git

If Git is installed on the system (sudo apt install git), the repository can be cloned directly from the github repository. Doing it this way means only a simple command needs to be run in order to install updates.

1. cd ~/Documents means any future commands will be executed in the user's Documents directory
2. git clone https://github.com/Joppleganger/GCARE-OPCN3.git clones the github repository to the user's documents folder

To update the repository, use the following code:

1. cd ~/Documents/GCARE-OPCN3 means any future commands will be executed in the git repository
2. git pull updates any necessary files

Step 4: Run setup script

In order to setup the necessary components for the OPCN3 datalogger to run, the setup.sh script has to be run.

1. cd ~/Documents/GCARE-OPCN3 means any future commands will be executed in the git repository
2. ls lists all files in the directory, this allows you to check the setup file is present.
3. bash setup.sh or ./setup.sh runs the setup script. The users password is required as some commands require to be run as the superuser.

It isn't advised to run unknown code with elevated permissions, so ensure you've read the contents of setup.sh to ensure you know what it will do beforehand. This code is provided as is, without warranty of any kind, either express or implied. The setup script grants the user permission to access serial devices, in this case the OPC-N3, installs tools needed for Python3 and creates a Python3 virtual environment that contains the packages necessary for the program to operate.

(Optional) Step 5: Extra features

The repository also contains GCARE-extras.sh. This script is specifically for the GCARE use case though others may find it useful. It currently performs the following functions:

• Creates a shortcut on the desktop, initialising the program. There are currently some issues and in some cases the shortcut requires manual intervention to 'Allow Launching'
• Creates an autorun script in ~/.profile, running the program on login

1. cd ~/Documents/GCARE-OPCN3 (or whichever directory the repository has been saved in)
2. ls lists all files in the directory, this allows you to check the GCARE-extras file is present.
3. bash GCARE-extras.sh or ./GCARE-extras.sh runs the extras script. The users password is required as some commands required to be run as the superuser.

It isn't advised to run unknown code with elevated permissions, so ensure you've read the contents of GCARE-extras.sh to ensure you know what it will do beforehand. This code is provided as is, without warranty of any kind, either express or implied.

The program can then be initialised by double clicking the shortcut on the desktop, as well as running on login.

(Optional) Step 6: USB permissions

usb-permissions.sh was created in a response to the program not having the correct permissions to write data to external media. When run, usb-permissions.sh iterates over all removeable media currently plugged in to a device and adds each device to /etc/fstab. This will add every device in your user's media folder to /etc/fstab, so manual addition of your USB device may be a better option for some.

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API

main.py

Functions

fancy_print

Makes a nicer output to the console

Keyword Arguments

Argument	Type	Usage	Required?	Default
str_to_print	str	String that gets printed to console	Y	None
length	int	Character length of output	N	70
form	str	Output type (listed below)	N	NORM
char	str	Character used as border, should only be 1 character	N	\U0001F533 (White box emoji)

Valid options for form

Option	Description
TITLE	Centres the string, one char at start and end
NORM	Left aligned string, one char at start and end
LINE	Prints a line of char of specified length

find_valid_path

Searches the /media/ and /mnt/ directories to find a device to save data to. If either zero or more than one devices are present in /media/, /mnt/ is searched. If the same is true of /mnt/, the path used is ~/Documents/OPC Data/

Keyword Arguments

None

Returns

If 1 directory present in /media/, returns path to that directory plus "/OPC Data/" Else if 1 direction present in /mnt/, returns path to that directory plus "OPC Data/" else returns "~/Documents/OPC Data/"

first_measurement_time

Calculates when the first measurement should take place

Keyword Arguments

Argument	Type	Usage	Required?	Default
timeInterval	str	Dictates the time interval between measurements. Options below	Y	"1m"
currentTime	datetime	The current time	Y	None

Options for timeInterval

Argument	Interval
1m	1 minute
5m	5 minutes
10m	10 minutes
15m	15 minutes
30m	30 minutes
1h	1 hours

Returns

timedelta object representing the amount of time until the first measurement

next_measurement_time

Calculates when the next measurement should take place

Keyword Arguments

Argument	Type	Usage	Required?	Default
timeInterval	str	Dictates the time interval between measurements. Options below	Y	"1m"
currentTime	datetime	The time the last measurement took place	Y	None

Options for timeInterval

Argument	Interval
1m	1 minute
5m	5 minutes
10m	10 minutes
15m	15 minutes
30m	30 minutes
1h	1 hours

Returns

timedelta object representing the amount of time until the next measurement

save_to_file

Appends recorded data to daily measurement file in OPC directory, creating a file with appropriate headers if one doesn't exist.

Keyword Arguments

Argument	Type	Usage	Required?	Default
opcData	dict	Measurements made by the OPC and headers for csv. Split into four keys. "Headers", "Data", "Bin Headers", "Bin Data"	Y	None
timestamp	datetime	When the measurement was made	Y	None
filePath	str	Path to save file to	Y	None

bin_Nones

Returns blank measurements for the bin columns if bin data was previously measured but is no longer.

Keyword Arguments

None

Returns

A row of 24 None values in csv format

OPCN3.py

Classes

Used to communicate with Alphasense OPC-N3 via USB-SPI connection.

SPIBytes

Dataclass containing ytecodes that command the OPC to perform various functions

Attributes

| Attribute | Type | Description | Value | | adUSBAdapter | int | Address for the USB adapter | 0x5A | | adOPC | int | Address for the OPC-N3 | 0x61 | | pCommand | int | Control byte for OPC-N3 peripheral | 0x03 | | fanOff | int | Disables fan | 0x02 | | fanOn | int | Enables fan | 0x03 | | laserOff | int | Disables laser | 0x06 | | laserOn | int | Enables laser | 0x07 | | reqHist | int | Requests histogram data | 0x30 | | reqData | int | Requests PM data and resets histogram | 0x32 |

OPCN3

Class representing the OPC-N3

Keyword Arguments

Argument	Type	Usage	Required?	Default
serialConfig	dict	Contains all necessary info for pySerial3 to make a connection	Y	None
deviceConfig	dict	User generated config file indicating operating parameters of the instrument	Y	None

Attributes

Attribute	Type	Description
opc	serial object	Serial connection to OPC-N3
wait	float	Time to wait between messages
isFanOn	bool	Is the fan on?
isLaserOn	bool	Is the laser on?
config	dict	User generated config file indicating operating parameters of the instrument
latestData	dict	Data output by OPC-N3. Defaults to None if OPC does not send data or data is not in expected format

Methods

initConnection

Initialises connection with OPC-N3

• Keyword Arguments

None

fanPower

Toggles OPC-N3 fan power status

• Keyword Arguments:

Argument	Type	Usage	Required?	Default
status	bool	True to enable fan, False to disable	Y	None

laserPower

Toggles OPC-N3 fan power status

• Keyword Arguments:

Argument	Type	Usage	Required?	Default
status	bool	True to enable fan, False to disable	Y	None

getData

Request histogram data from OPC-N3

• Keyword Arguments:

None

• Returns:

None, but stores measurements in latestData attribute

formatData

Formats data saved to latestData attribute into csv format

• Keyword Arguments:

None

• Returns:

dict with 4 keys:

• "Headers": Headers for non bin measurements
• "Data": Non bin measurements
• "Bin Headers": Headers for bin measurements
• "Bin Data": Bin measurements

If no measurements are made, all are None. If bin measurements aren't made, "Bin Headers" and "Bin Data" is None

printOutput

Returns data stored in latestData in a format to be printed to the terminal

• Keyword Arguments:

None

• Returns:

Formatted str containing measurement data

Methods

convert_RH

Converts raw RH output of OPCN3 to float value

Keyword Arguments

Argument	Type	Usage	Required?	Default
rawRH	int	Raw RH measurement from OPC-N3	Y	None

Returns

Converted RH measurement

convert_T

Converts raw T output of OPCN3 to float value

Keyword Arguments

Argument	Type	Usage	Required?	Default
rawT	int	Raw RH measurement from OPC-N3	Y	None

Returns

Converted T measurement

combine_bytes

Combines Least Significant Byte and Most Significant Byte in to a 16 bit integer

Keyword Arguments

Argument	Type	Usage	Required?	Default
LSB	int	Least significant byte	Y	None
MSB	int	Most significant byte	Y	None

Returns

16 bit int representing a combination of LSB and MSB

Components

Prototype

The prototypes of these sensors used the following components:

1. Raspberry Pi 4 Model B 4GB (Running Ubuntu Desktop 20.04 LTS 64 bit)
2. OKDO Raspberry Pi 3 7" Touchscreen Display (Compatible with RPi 4)
3. Alphasense OPC-N3
4. Alphasense USB-SPI Bridge
5. Verbatim 32 GB Micro SD Card
6. Verbatim 64 GB USB3 Memory Stick