This is the English version for educators of the project PhyPiDAQ, a package for acquisition, storage, visualization and analysis of measurement data with the Raspberry Pi.
Hier gibt es die Deutsche Version.
In this document, the entire PhyPiDAQ workflow, starting from the
Installation up to descripotions of concrete experiments is described.
- PhyPiDAQ documentation (for teachers)
PhyPiDAQ is a project for transparent, easily understandable Data Acquisition (DAQ) with a Raspberry Pi. The software contains basic functions for data acquisition and visualization such as data logger, bar graph, XY or oscilloscope display and data recording on disk for subsequent evaluation.
The user interface is designed in such a way that pre-made templates for many sensors can be used to read them out quickly and easily. In addition, it also offers the option of changing parameters like, e. g. sampling rate, range, axis labeling, function evaluation for direct conversion of raw measurements of special sensor settings. The settings can be conveniently saved and recalled so that initial examples for own experiments or for a quick demonstration can be easily provided.
A large number of sensors, such as various analog-digital converters, current sensors, environmental data sensors, gamma ray detectors or a usb-oscilloscope, are supported. Here, widespread and inexpensive sensors were used, which have a sufficient level of accuracy that is more than sufficient for school experiments.
The sensors can be individually connected to the Raspberry Pi using jumper cables, or via a printed board specially designed for use with the PhyPiDAQ software on which some sensors and amplifiers are permanently attached. The latter set-up reduces cabling efforts to a minimum and experiments can be set up quickly. A 3d printed connection panel and a printed circuit-board are available so that all components can be conveniently provided in an organizer case.
Fig. 1: Representation of the time dependence of two signal sources
(square wave and capacitor voltage) connected to an AD converter
Fig. 2: Measurement case with Raspberry Pi, circuit board and built-in display
Sensors and standard amplifiers are at the heart of the PhyPiDAQ project. A number of analog and digital sensors are supported by the PhyPiDAQ software, which is open source and can be downloaded from the Github repository. The detailed installation procedure is described here.
Sensors can be directly conneted to the GPIO pins of your Raspberry Pi, and an external breadboard may be used to provide amplification of weak signals, if necessary.
A proposal for a case containing some of the most common sensors to measure voltages and currents and a set of standard amplifiers is proposed as part of the PhyPiDAQ project. Detailed building instructions and a liste of recommended compontents are described in the folder MeasuringCase, which you can also find on the Github repository.
If there already is an operating system on the Raspberry Pi, you can continue directly with 3.2. If not, proceed with this description how to install the operating system.
First download Raspberry Pi Imager from the official website
https://www.raspberrypi.org/downloads/ to any computer with an SD card slot.
Install the Raspberry Pi Imager by double-clicking the downloaded file.
Fig. 3: Installation of Raspberry Pi Imager, double click on the "Raspberry"
A new window opens in which you can select the operating system to be installed and the SD card. Under Operating System select "Raspberry Pi OS (other)" and then "Raspberry Pi OS Full".
Fig. 4: Selection of the operating system
Fig. 5: Selection of the operating system
Insert the SD card into the slot of the computer. Ensure that the SD card is in writable mode by pushing the small slide on the left edge of the SD card adapter upwards.
Fig. 6: Make the SD card writable, move the slider to the top position
In the Raspberry Pi Imager you can now select your SD card by clicking on "SD Card".
Fig. 7: Selection of the SD card
By clicking on "Write" and then confirming, you can finally record onto the SD card; you may be asked for the password once. This process can now take a few minutes.
Fig. 8: Writing to the SD card
When the process is complete, the operating system for the Raspberry Pi is on the SD card and this can be plugged into the Raspberry Pi. If you have not decided to use the case version with a display, connect an external monitor and make sure that a mouse and keyboard are connected. Also connect an Ethernet cable if you don't have a WiFi connection available. Then you can connect the Raspberry Pi to the power supply, and it boots automatically. Various packages are now installed automatically, which can take several minutes. If this is successful, a window opens in which you can set basic system settings such as time zone, country, keyboard layout and your WiFi network, if this is desired. The installation of the Pi is now complete and we can continue installing PhyPiDAQ.
The operating system of the Raspberry Pi is a Linux system that comes with many programmes by default. Part of the Linux operating system is to frequently use the command line, which is similar in many respects to the "command line" under Windows. As a modern operating system, Linux of course also has a very comfortable graphical user interface in which you can start and control applications with the and control applications with the mouse. The programme names for common applications sometimes deviate from the usual. An overview can be found in the list below.
List of the most important applications under Linux on the Raspberry Pi
| Programm | Description |
|---|---|
LXTerminal |
Linux console for command input |
leafpad |
Simple editor for text files |
gedit |
Editor for text files with advanced possibilities (e.g. syntax highlighting) |
qpdfview |
Display pdf documents |
gpicview |
Image viewer |
idle3 |
simple development environment for python (vers. 3) |
Thonny |
Development environment for Python programs with debugger and single step |
libreoffice |
Word processing, spreadsheet and presentation |
chromium-browser |
Web-Browser |
Mathematica |
Computer algebra, very powerful |
pi-packages |
Graphical manager for software packages |
apg-get |
Command line tool for installing and deleting software packages |
git |
Source code management system for downloading, modifying and publishing programme packages; usually linked to an account on https://github.com |
If one of the listed programmes is not available, it can easily be installed in exactly the same way as other programme packages on the command line,
with the command sudo apt-get install <name>. Almost all of the listed programs can also be installed via the
graphical user interface of the Raspberry Pi from the programme menu.
The most frequently used commands in the console (LXTerminal, see list above) are briefly described in the table below.
briefly described in the table below.
List of the most important commands for the command line.
| Command | Beschreibung |
|---|---|
ls |
Lists all files in the current directory |
cd folder |
Switches to the specified folder |
cd |
Switches to the home directory |
pwd |
Displays current (working) directory |
cp file1 file2 |
copies file1 to (new) file2 |
mv file1 file |
Rename file with file1 to file2 |
mkdir folder |
creates a folder with the name folder. |
rmdir folder |
Remove folder folder (must be empty) |
sudo nano file |
creates/opens a new file file. |
rm file |
Deletes the specified file |
pyhton3 file.py |
Executes file file.py in python3. |
./file.py |
alternatively: execute file file.py. |
cat file |
displays content of the file with name file. |
less file |
Displays contents of a file (up and down with arrow keys, end with q) |
man Befehl |
displays auxiliary information for the specified command. |
| Arrow key up/down | displays last used commands |
| Arrow key right/left | Edit command |
<Str> + <c> |
Exits the programme running in the terminal |
<Str> + <z> |
Moves the programme running in the terminal to the background |
bg |
Continues the programme that has been moved to the background |
jobs |
Displays all processes running in the term. |
kill %i |
stops process with number i (see command jobs) |
Command& |
executes command as a background process |
date |
Displays date and time |
/ in file name separates subfolder from folder or file name |
|
~/ in file specification stands for the home directory |
|
* in filename stands for any character string |
|
? in file or directory name stands for any character |
|
./ in path to file stands for the current directory |
|
Command > file name |
Ausgabe von Befehl in Datei mit Namen Dateiname speichern |
Command1 | Command2 |
Output of Command1 as input to Command2. |
sudo Command |
executes command as administrator (with "superuser rights") |
sudo reboot |
Reboot system |
sudo halt |
Stop system (can be switched off afterwards) |
Obtaining the PhyPiDAQ code and easy installation
Please note that your Raspberry Pi must be connected to the Internet for
the following steps. Open the terminal, which you can find in the system
bar at the top left.
Fig. 9: Open the terminal
First install the repository manager git, which is used to download all
files of the PhyPiDAQ package from its github repository.
To do this, enter the following text in the terminal window:
bash sudo apt-get install git
Fig. 10: Enter command in the terminal
Enter the following commands to install PhyPiDAQ. Always copy this code line by line into the terminal and confirm each command with the Enter key. DO NOT insert all lines at once.
mkdir ~/git
cd ~/git
git clone https://github.com/PhyPiDAQ/PhyPiDAQ
cd ~/git/PhyPiDAQ
./installlibs.sh
The installation is now complete and PhyPiDAQ is ready for the first use.
If you want to update the installed version later, enter the following in the terminal (not necessary for the first installation, as the current version has already been downloaded):
cd ~/git/PhyPiDAQ
git pull
./installlibs.sh
For every-day use of the PhyPiDAQ software it is very convenient to draw a copy of the relevant files of the installation in the user's home directory by executing
./install_user.sh
This script generates a directory named PhyPi and copies useful scripts and examples. It also creates desktop icons for an easy start of the graphical user interface.
To start the PhyPiDAQ application, double-click the icon on the desktop PhyPi.
Fig. 11: Open PhyPiDAQ
You will be asked how you would like to open it, select "Run" here. Two windows open now: a black terminal window, which shows current status messages and log files. You can ignore this window for ease of use. It only gets important when errors are displayed. In this case, the terminal window shows the error code and instructions which point to the problem and which can usually be used to fix the problem quickly. The more important window is the user interface of PhyPiDAQ.
Fig. 12: User interface PhyPiDAQ
The tab "Control", in which you are after opening, is the start tab. A measurement can be started from here by clicking the button "StartRun" at the bottom right, but this should only be tried later. The so-called working directory can also be selected in this tab. Here you can determine where the configured experiment should be saved. A clear folder structure is essential if PhyPiDAQ is used in several school classes. So it is highly recommended to use a structure like the following:
Fig. 13: folder structure
You can create new folders in the file manager (similar to Windows "My Computer" or Mac "Finder") by right-clicking on "New" -> "Folder" in the window.
Fig. 15: create a new folder
Another possibility is to enter the following command in the terminal, which creates the subfolder "class_12" in the folder "school".
mkdir /home/pi/PhyPi/school/class_12In the PhyPiDAQ user interface you select in the field "Work Dir:" in which folder you want to save the current project. Below that, in "DAQ config", you can open projects that have already been saved. This is particularly useful if you have already tested an experiment in advance and want to demonstrate it in class. The saved project will then be opened again in exactly the same way and you can start the experiment immediately. Below, in the field "Name" you can enter the name of the experiment. This will appear in the file name. If you click on "Save Config", you save the configuration file. The file will then be called "default.daq" if you wrote "default" in Name:. Each time you start the program with "StartRun", an additional file is created with name, time and date, which is saved in the directory you specified for "Work Dir", e.g. school/class_12/photoeffect.
Task: Now create a folder structure as shown in Fig. 30 with your school classes. Create a folder with the name "Test" in one of these classes. Then switch to the PhyPiDAQ user interface and select the test you just created in Work Dir. Now assign the name "standard experiment" and save the project. Then verify in the file manager that the created project is there.
We now want to familiarize ourselves with the second tab, "Configuration". Click on the tab "Configuration".
Fig. 16: configuration
A window can now be seen in which all parameters for the experiment can be
set, such as:
- which sensor do I use (DeviceFile)?
- which maximum values should be displayed in the diagram (ChanLimits)?
- should the values of the sensor be converted directly (ChanFormula)?
- which axis labeling should be displayed (ChanLabels)?
- which formulas should be displayed (ChanUnits)?
- how often should be scanned (Interval)?
and many more...
Don't let this put you off! These parameters represent ways in which an experiment can be expanded or perfected. By no means all parameters are required - usually around 3-5 lines are sufficient. In the "default" - Config, which can be seen in Fig. 32, all setting options are indicated and can be commented out by a "#" at the beginning of the respective line.
If you want to make changes to this configuration, you must first activate the "Edit Mode" at the top right by clicking on it once. The field in front of it shows that you can now write into the text field. Helpful Keyboard shortcuts are:
- Str + C for copying selected characters
- Str + V for pasting the characters you just copied
- Str + Z for undo
- Str + Shift + Z to undo again.
Always start by telling the software which sensor you want to read out by removing the "#" at the beginning of the corresponding line.
We now want to read out the ADS1115 analog-to-digital converter demonstratively and therefore change the line
#DeviceFile: config/ADS1115Config.yaml # 16 bit ADC, I2C busto
DeviceFile: config/ADS1115Config.yaml # 16 bit ADC, I2C busYou can leave all other settings here unchanged, as suitable parameters for this
sensor are automatically selected. Changes may have to be made to the sensor,
because e.g. it has four inputs but not all of them have to be
read out depending on the project. To do this, click on "reload device config",
which you will find at the bottom right. A confirmation follows that PhyPiDAQ
has now accepted the selected sensor.
Now click on the tab "Device Config" at the top. The parameters of the sensor can be seen now.
Fig. 17: Configuration of the sensor
Here the syntax is the same again, that means:
- Lines that begin with "#" are commented out and have no function on the program
- To make changes you have to go to "Edit-Mode" by clicking above on the "Edit-Mode" field on the right.
You now have the choice of which channels you want to read out, as determined in "ADCChannels". If you only want to read out channel 1, this is the line:
ADCChannels: [0]because counting starts at zero. If you only want to read out channel 2, this is the line:
ADCChannels: [1]You can read out several inputs at the same time by separating the individual channels with commas:
ADCChannels: [0, 1, 2, 3]The other parameters below can be used if necessary, for example to subtract one input from another. To do this, follow the instructions in the corresponding lines. Please note that if you want to read out several channels, you also have to adjust the parameters below to the respective number of channels. So the following is not possible and will lead to an error message:
# example of a configuration file for ADC ADS1115
DAQModule: ADS1115Config
ADCChannels: [0, 1, 2, 3] # active ADC-Channels
DifModeChan: [false] # enable differential mode for Channels
Gain: [2/3] # programmable gain of ADC-Channel
sampleRate: 860 # programmable Sample Rate of ADS1115Correct is:
# example of a configuration file for ADC ADS1115
DAQModule: ADS1115Config
ADCChannels: [0, 1, 2, 3] # active ADC-Channels
DifModeChan: [false, false, false, false] # enable differential mode for Channels
Gain: [2/3, 2/3, 2/3, 2/3] # programmable gain of ADC-Channel
sampleRate: 860 # programmable Sample Rate of ADS1115We have now selected the sensor ADS1115 with four channels. You can now assign a name below and save the configuration.
Now connect the analog-digital converter to the Raspberry Pi - four wires are required:
GND and + 5V for the power supply and SCL and SDA for the i2C connection for the data
transmission from the sensor to the Pi.The exact wiring with the breadboard is explained in Course digital data acquisition.
Then you can click the button "StartRun". A window with the diagram opens and you can start the measurement by clicking at the bottom left on "Run". Congratulations, you have taken your first measurement with PhyPiDAQ! Fig. 18 shows the graphical display you should see.
Fig. 18: Reading out four channels with an analog-digital converter
There are numerous ways in which you can interact wiht PhyPiDAQ. On the one hand, it is important to be able to save recorded data, which is done with the button "SaveData". The values are saved in the folder selected in the working directory ("WorkDir") in the folder belonging to the measurement. By default, only the first 12 seconds are saved, which is exactly the interval that can be seen in the display. In the configuration this can of course be adjusted and extended if desired. The standard data format is ".csv", which can also be adapted.
Keyboard shortcuts are defined for all buttons, as indicated by the '_' on the button text. In many practical cases, typing a button is much easier than interacting via the mouse.
We are now ready to read out a large number of different sensors, graphically plot them live on the monitor and export the values. That opens up countless possibilities to use PhyPiDAQ in the classroom.
There is an introductory Course,
Course for digital data acquisition.
Starting with very basic material on digitization and data processing with Python,
a first project deals with a non-linear, temperature dependent resistor, an NTC,
which is first calibrated and then used in a self-made thermometer.
As a more advanced example involving active amplification of a weak signal, a load-cell
as contained in standard kitchen scales is used to build a very sensitive force sensor.
Some parts already available:
More advanced experiments from different areas of Physics are described below to illustrate the entire PhyPiDAQ workflow from start to end.
List of experiments with PhyPiDAQ
An appliction of PhyPiDAQ in a realistic school project with documentaion of a large number of typical physics experiments is documented here:
-
M. Wong, G. Quast, D. Braig, Implementing a Raspberry Pi based Digital Measurement System in Undergraduate Physics Education, European J of Physics Education, v. 11 n. 3 1-16 (Nov. 2020), DOI 10.20308/ejpe.v11i3.297
-
M. Wong, Project "Raspberry Pi based Digital Measurement System in Physics"