In this manual, the entire PhyPiDAQ workflow, starting from the
Installation up to the evaluation of experiments is described.
- What is PhyPiDAQ?
- What do I need and how do I assemble it?
- How do I set up the Raspberry Pi and install PyPiDAQ?
- How do I use the PhyPiDAQ software?
- How do I carry out experiments with it?
- electrostatics
- force sensor
- photo effect
PhyPiDAQ is a project for transparent, easily understandable Data AQuisition (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
The software is open source and can be downloaded from this Github page. The detailed installation is described here.
The following components are required for the measurement box:
| Description | Order number | Quantity | Supplier | Unit price in euros | Total price in euros |
|---|---|---|---|---|---|
| for the plug-in board: | |||||
| Miniature socket, 2mm black | MBI 1 SW | 9 | Reichelt | 0.79 | 7.11 |
| Miniature socket, 2mm red | MBI 1 RT | 8 | Reichelt | 0.79 | 6.32 |
| Miniature socket, 2mm green | MBI 1 GN | 8 | Reichelt | 0.79 | 6.32 |
| Miniature socket, 2mm yellow | MBI 1 GE | 9 | Reichelt | 0.79 | 7.11 |
| Miniature socket, 2mm blue | MBI 1 BL | 3 | Reichelt | 0.79 | 2.37 |
| Arduino - Grove universal socket, 4-pin (set of 10) | GRV CONNEC4PIN | 1 | Reichelt | 1.25 | 1.25 |
| Standard LED green 5 mm | RND 135-00122 | 1 | Reichelt | 0.06 | 0.06 |
| Standard LED red 5 mm | RND 135-00126 | 1 | Reichelt | 0.06 | 0.06 |
| Breadboard 400 holes | RND 255-00005 | 1 | Reichelt | 1.90 | 1.90 |
| Socket strip 2.54 mm, 1x20 | MPE 115-1-020 | 4 | Reichelt | 1.20 | 4.80 |
| Filament for 3D printer | 120g | ||||
| for the board: | |||||
| PCB board "PhyPiDAQ" | https://aisler.net/p/ABFAPVWM | 1 | Aisler | approx. 10 euros | approx. 10 euros |
| Operational amplifier, 1-way, DIP-8 | CA 3140 DIP | 1 | Reichelt | 0.99 | 0.99 |
| Instrumentation amplifier, 1-way, DIP-8 | AD 623 ANZ | 1 | Reichelt | 6.35 | 6.35 |
| Seven Darlington Arrays, DIP-16 | ULN 2003A | 1 | Reichelt | 0.30 | 0.30 |
| Operational amplifier, 2-way, DIP-8 | MCP 6042-I / P | 2 | Reichelt | 0.66 | 1.32 |
| DC-DC 5V converter | TMA 0505D | 1 | Reichelt | 5.50 | 5.50 |
| Analog / digital converter ADS1115 | RPI ADC 4CH | 1 | Reichelt | 3.30 | 3.30 |
| Rectifier diode | UF 4003 | 8 | Reichelt | 0.05 | 0.40 |
| Level shifter | DEBO LEV SHIFTER | 1 | Reichelt | 4.15 | 4.15 |
| INA219 current / voltage sensor | DEBO SENS POWER | 1 | Reichelt | 2.80 | 2.80 |
| Digital-to-analog converter | 802236543 - 62 | 1 | Conrad | 5.89 | 5.89 |
| Resistance 10 kOhm, 1% | VI MBA 02040C1002 | 6 | Reichelt | 0.05 | 0.3 |
| Resistance 1 kOhm, 0.1% | ARC MRA0207 1M B | 2 | Reichelt | 0.37 | 0.74 |
| Resistance 47 Ohm, 1% | VI MBB 02070C4709 | 6 | Reichelt | 0.03 | 0.18 |
| Resistance 100 Ohm, 1% | VI MBB 02070C1000 | 1 | Reichelt | 0.04 | 0.04 |
| Ceramic capacitor 10 nF | KERKO 10N | 1 | Reichelt | 0.06 | 0.06 |
| Ceramic capacitor 100 nF | KERKO 100N | 4 | Reichelt | 0.06 | 0.24 |
| Ceramic capacitor 100 pF | KERKO 100P | 4 | Reichelt | 0.05 | 0.20 |
| Electrolytic capacitor 47 μF | M-A 47U 100 | 4 | Reichelt | 0.21 | 0.84 |
| Electrolytic capacitor 10 μF | KS-A 10U 16 | 4 | Reichelt | 0.11 | 0.44 |
| Dot-strip grid board | H25PS200 | 1 | Reichelt | 2.60 | 2.60 |
| IC socket 16 poles | MPE 001-1-016-3 | 1 | Reichelt | 0.35 | 0.35 |
| IC socket 14 poles | MPE 001-1-014-3 | 1 | Reichelt | 0.29 | 0.29 |
| IC socket 8 poles | MPE 001-1-008-3 | 4 | Reichelt | 0.26 | 1.04 |
| Precision potentiometer | 64Y-100K | 2 | Reichelt | 0.21 | 0.42 |
| Ribbon cable | RPI T-COBBLER P | 1 | Reichelt | 3.60 | 3.60 |
| for case and Raspberry Pi: | |||||
| Raspberry Pi 4, 2 GB RAM | RASP PI 4 B 2GB RAM | 1 | Reichelt | 49.00 | 49.00 |
| Raspberry Pi charger | GOO 56746 | 1 | Reichelt | 8.50 | 8.50 |
| Display (optional) | RPI LCD 10.1HDMI | 1 | Reichelt | 102.10 | 102.10 |
| Power supply display | HNP 15-090L6 | 1 | Reichelt | 9.99 | 9.99 |
| Power supply | DEBO BREAD POWER | 1 | Reichelt | 4.50 | 4.50 |
| Memory card 32GB | SDSQUAR 032GGN6MA | 1 | Reichelt | 7.95 | 7.95 |
| USB hub | DESKHUB 60- SW | 1 | Reichelt | 6.00 | 6.00 |
| HDMI cable | RPI M-HDMI HDMI | 1 | Reichelt | 4.50 | 4.50 |
| Filament for 3D printer | 170 g | ||||
| Keyboard with mouse pad | LOGITECH K400PRO | 1 | Reichelt | 29.95 | 29.95 |
| USB A USB C cable | GOOBAY 55467 | 1 | Reichelt | 2.40 | 2.40 |
| Cooling case Raspberry Pi passive | 2140237 - 62 | 1 | Conrad | 15.49 | 15.49 |
| Jumper cable | 096853 - 62 | 1 | Conrad | 2.79 | 2.79 |
| Insulating tape | 1 roll | ||||
| Screws M2.5 20 mm | 4 | ||||
| Screws M3 12 mm | 7 | ||||
| Washers for M3 screws | 14 | ||||
| Pillar connector, 40-pin, with locking, angled | PSL 40W | 1 | Reichelt | 0.49 | 0.49 |
| Universal case | 8519544 | 1 | Hornbach | 17.95 | 17.95 |
| Accessories: | |||||
| Measuring line 15 cm red, 2mm | 1385668-62 | 2 | Conrad | 2.49 | 4.98 |
| Test lead 15 cm green, 2mm | 1385671-62 | 2 | Conrad | 2.49 | 4.98 |
| Measuring line 15 cm blue, 2mm | 1385669-62 | 2 | Conrad | 2.49 | 4.98 |
| Test lead 15 cm black, 2mm | 1385667-62 | 2 | Conrad | 2.49 | 4.98 |
| Test lead 15 cm yellow, 2mm | 1385670-62 | 2 | Conrad | 2.49 | 4.98 |
| Test lead 30 cm red, 2mm | 1385676-62 | 2 | Conrad | 2.49 | 4.98 |
| Test lead 30 cm black, 2mm | 1385675-62 | 2 | Conrad | 2.49 | 4.98 |
| Adapter plug, 2 mm plug / 4 mm socket, red | MZS2RT | 2 | Reichelt | 1.45 | 2.90 |
| Adapter plug, 2 mm plug / 4 mm socket, black | MZS2SW | 2 | Reichelt | 1.45 | 2.90 |
| Adapter plug, 4 mm plug / 2 mm socket, red | MZS4RT | 2 | Reichelt | 2.30 | 4.60 |
| Adapter plug, 4 mm plug / 2 mm socket, black | MZS4SW | 2 | Reichelt | 2.30 | 4.60 |
| Other: | |||||
| Superglue | |||||
| Heat shrink tubing | |||||
| Total: | |||||
| without display | 284.52 | ||||
| with display | 401.11 | ||||
First the socket headers (Reichelt, MPE 115-1-020) are clipped to the appropriate lengths. These are required:
- 3 x 1 pin
- 7 x 2 pins
- 1 x 3 pins
- 5 x 4 pins
- 3 x 5 pins
- 4 x 6 pins
- 1 x 10 pins
These are soldered to the corresponding holes marked by squares on the board. The other components are also soldered according to the labeling on the board. Pay attention to the polarity of the electrolytic capacitors - the side marked in white corresponds to the minus pole. Resistors and ceramic capacitors do not have any polarity. The brackets for the ICs are soldered in such a way that the semicircular recess matches the label. This shows in which direction the IC must be inserted.
In the picture on the left you can see two places for resistors and two for capacitors, which remain free. These are provided so that pull-up resistors and capacitors can be installed to ground in the event of interference on the I²C bus. But at first, these places should remain free.
Finally, the connection pins that are too long can be clipped off on the back. The components are placed on the respective brackets.
Fig. 3: soldering, step 1
Fig. 4: Soldering, Step 2: The female headers are attached
Fig. 5: Soldering, step 3: The other components are soldered on. The four devices marked
in red are released
Fig. 6: soldering, step 4: the finished board
- Fig. 7*: The finished board with all components
The following part describes how the PhyPiDAQ hardware with the circuit board, an optional display and wireless keyboard can be attached to a standard organizer case, so that everything can be stored in a spacious, space-saving and secure manner.
First the 3D models are printed in the Hardware/3D_Modelle folder. Depending on the printer, it may be advisable to rotate the models accordingly and use a support structure. Good results have been achieved with PLA filaments. When the printed models are finished, the construction of the case can begin.
First, the 30 cm long breadboard connectors (C *, 096853-62) are cut once in the middle to obtain that 15 cm long cables. A total of 46 of such short cables are required. The cut side is stripped and soldered to the 32 2 mm sockets (R *, MBI1SW and other colors). The connectio pins of a red (R *, RND 135-00126) and a green LED (R *, RND 135-00122) are also soldered to the cables and insulated, as well as the two grove sockets (R *, GRV CONNEC4PIN) and two pin headers (R *, RPI HEADER 40).
Fig. 7: Box construction, step 1: Prepare plug connections
Next, the printed breadboard is drilled through with a 5mm wood drill in the designated places. The square cutouts for the Grove connections and the pin headers can be drilled through with a handpiece, for example.
The 2mm sockets can now be inserted and fixed with screws according to the illustration below. The LEDs, Grove sockets and pin headers are attached to the holes provided with superglue. The breadboard is attached to the connection panel with the adhesive tape on its back. The labels are printed out and glued at the appropriate places.
Fig. 8: Box construction, step 2: equipping the printed plug-in board with cables
Fig. 9: Box construction, step 3: Stick the lettering on the plug-in plate 
The case can be processed while the superglue is hardening.
First, the hole of the printed holding rod is drilled through with a 3mm drill. This is
then drilled into the left inside of the case in such a way that the cover is held by the
rod with slight pressure, thus preventing unintentional closing. A M3x16mm and lock
nut can be used as a screw.
Fig. 10: Box construction, step 4: screw on the retaining rod 
Now the brackets for the circuit board and the breadboard are screwed to
the floor. For this purpose, the circuit board is clamped so that the
spacing between the brackets is correct. The distance between the brackets
in the back and front of the case should be 3.2 cm and 6.5 cm to the left.
Suitable screws are M3x12mm, which are screwed upside down so they don't
scratch the surface later.
Fig. 11: Case construction, step 5: Screw on the circuit board 
The hole for the USB hub (R *, DESKHUB 60-SW) is made with a 60 mm drill
collar on the right side of the case at the back. The USB hub can now be
glued into the socket with hot glue or super glue.
Fig. 12: Case construction, step 6: Drill a hole for the USB hub
Next, the display connected to the cable is clamped in the printed frame and
attached to the cover with M3x10mm screws. The nuts point to the inside of
the case. The distance from the display to the bottom is a maximum of 5 cm,
so that the cables still reach the controller. The display controller is
provided with the cables and the control unit is screwed to the printed
bracket with M3x10mm screws. The controller can now be clicked in. The
bracket can then be attached to the case with M3x12mm screws as shown in
the illustration. The distance to the right should be at least 6 cm so that
the connections are still accessible. In the case of a cable, the location
on the controller is not clear. The color coding of the cables helps here:
the red cables (mostly) represent positive voltages. The right place can be
found with the labeling of the controller.
Fig. 13: Box construction, step 7: Wire the display controller
Fig. 14: Case construction, step 8: Screw on the display controller 
When the superglue has dried, the plug-in board can be connected to the
circuit board. The connections are shown below:
Fig. 15: Box construction, step 9: Wire the plug-in plate to the circuit board
Next, the Raspberry Pi is mounted. To do this, the Pi is first held in
the right place on the display controller housing in order to put the drill
holes on it. Then the cooling housing (C *, 2140237 - 62) is attached to
the Pi. For this purpose, the three heat-conducting plates are attached to
the appropriate places, whereby the foils on the top and bottom must be
removed. The heat sink is screwed to the display controller bracket using
the M2.5x25mm screws. The bracket with the Pi can now be attached to the
case with M3x12mm screws.
Fig. 16: Case construction, step 10: attach Raspberry Pi heat sink
Fig. 17: Case construction, step 10: Screw the Raspberry Pi onto the display controller 
Fig. 18: Case construction, step 10: Attach the display controller housing to the case 
Finally, the Raspberry Pi is attached to the board via the extension pins
(R *, RPI HEADER 40) with the 40-pin cable (C *, RPI T-COBBLER P). The
power supply units for the board and display are also connected. The USB
hub is connected to the Raspberry Pi. The dongle of the wireless keyboard
(R *, LOGITECH K400PRO) is plugged into the USB port of the Pi. The HDMI
port of the Raspberry Pi is connected to the display controller with the
corresponding adapter (R *, RPI M-HDMI HDMI). The HDMI adapter (R *, DELOCK
65391) is plugged into the other port of the Raspberry Pi and can be fixed
in the USB hub with adhesive so that another external display can be
connected. The power port of the Raspberry Pi is connected to the power
supply of the board (R *, DEBO BREAD POWER) with the adapter (R *, GOOBAY
55467). The keyboard can be stored on the plug-in board when the cover is
closed. The cables and adapters are sorted into the three compartments.
Fig. 19: all parts with display and keyboard can be found in the case
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. 20: 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. 21: Selection of the operating system
Fig. 22: 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. 23: 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. 24: 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. 25: 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.
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. 26: 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 texxt in the terminal window:
bash sudo apt-get install git
Fig. 27: 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/GuenterQuast/PhyPiDAQ
cd ~/git/PhyPiDAQ
./installlibs.sh
cp ~/git/PhyPiDAQ/phypi.desktop ~/Desktop/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.shTo start the PhyPiDAQ application, double-click the icon on the desktop PhyPi.
Fig. 28: 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. 29: 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. 30: 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. 31: 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. 32: 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. 33: 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, what is
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, via which the sensor transmits data to the Pi.
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. 34: Reading out four channels with an analog-digital converter
There are now numerous ways in which you can use PhyPiDAQ. On the one hand,
it is important to be able to save recorded data, which is done with
"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.
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. We will now describe three
sample experiments so that you can see what the entire workflow can look like
from start to finish.
In the following experiment, the effect of electrostatic influence will be shown.
Furthermore, the same setup can also be used to demonstrate a load spoon.
An open, round capacitor plate with a diameter of d ≈ 5 cm is connected to the
electrometer. The mass of the measuring case is pulled to the earth potential.
A capacitor with a capacity of 1 nF is connected between the capacitor plate
and the earth. The output of the electrometer is connected to the level converter
and this in turn to the ADC. This means that both positive and negative
voltages can be read out.
elektrostatik.daq:
Fig. 34: Electrostatic experiment setup
We now deal with the configuration file.
For the sake of clarity, superfluous comments and lines that have been commented
out have been left out.
DeviceFile: config/myADS1115Config.yaml # 16 bit ADC, I2C bus
ChanLabels: ['Uc'] # names for channels
ChanUnits: ['V'] # units for channels
ChanColors: [darkblue] # channel colours in display
ChanFormula:
- 2*c0-5 # chan0
Interval: 0.1 # logging interval
DisplayModule: DataGraphs # text, bar-graph, history and xy-view
Title: "Data from File" # display titlemyADS1115Config.yaml:
# example of a configuration file for ADC ADS1115
DAQModule: ADS1115Config
ADCChannels: [0] # active ADC-Channels
DifModeChan: [false] # enable differential mode for Channels
Gain: [1] # programmable gain of ADC-Channel
sampleRate: 860 # programmable Sample Rate of ADS1115 You may have to adjust the Gain in the penultimate line - depending on whether
the displayed signal is too small or too large. On the software side, the function
of the level converter is compensated as follows:
Ucapacitor = 2 · Umeasured-5V, which is already taken
into account in ChanFormula. Before the measurement begins, the capacitor plate
is connected to earth potential using a conductor so that it is uncharged. If a
charged body is brought closer to the capacitor plate, the electric field of the
charged body causes a force on the free electrons of the capacitor plate, which
then - depending on the body's charge - are accelerated towards or away from it
(influence). This process is limited by the fact that an electric field is built up
through the charge shift, which counteracts the accelerating force. The charge
separation can be measured as an electrical voltage that is applied between earth
and the capacitor plate, i.e. precisely on the input side of the electrometer. It
should be noted that an electrometer with a very high internal resistance is
absolutely necessary for this experiment, as otherwise the greater current flow
between the input of the electrometer and the earth leads to a charge equalization
on the capacitor plate and the effect is therefore not visible. The effect is not
visible with a conventional multimeter. A plastic rod is used as the body, which
was rubbed on a wool sweater so that it became charged. Then it is brought closer
to the capacitor plate, the distance being varied several times. The curve recorded
in the figure below shows the time course of the voltage across the capacitor. The
change in tension with the distance between the rods can be clearly seen. The sign
of the voltage also shows that the rod is positively charged.
Fig. 35: Influence Time curve of the voltage on the capacitor with repeated
changes in the distance to the charged rod.
Now the demonstration of the load spoon follows. To do this, a metal ball is rubbed
on a wool sweater and then the discharged capacitor plate is touched with it. The
illustration shows the course of the voltage. The increase in the capacitor voltage
upon contact with the sphere indicates the charge. With Q = C · U, a known
capacitance of 1 nF and the voltage difference of −2.7 V, the transferred charge is
−2.7 nC.
Fig. 36: Charge spoon Time curve of the voltage on the capacitor when
approaching and touching a charged ball. At approx. 66 s the capacitor is grounded
so that the voltage is 0 V. When the charged sphere approaches, the amount of
voltage on the capacitor increases due to influence. When the ball touches the
capacitor plate (t ≈ 67.9 s), the voltage reaches a constant value.
A force measurement is to be carried out using a load cell. It is checked whether
the voltage applied to the load cell increases linearly with the attached mass, as
expected.
The schematic structure is shown below:
Fig. 37: force sensor schematic structure
The load cell used can be rebuilt according to these instructions.
First, the load cell is supplied with an operating voltage of U=5V and screwed
to a device so that weights can be attached to it. The voltage difference between
the two outputs of the load cell is a measure of the applied force. Since this
difference is typically in the mV range, the voltage is amplified using the
instrumentation amplifier. The output of the instrumentation amplifier is connected
to input A0 of the ADC. Since the necessary gain factor is unknown, it is initially
set small and then increased during the measurement until the signal is in a
suitable value range. Since the polarity of the voltage is also unknown, a
reference voltage is tapped and connected to the associated connection of the
instrumentation amplifier.
This shifts the output voltage by the value of the reference voltage so that
negative voltages can be shifted to positive voltages. Approx. 2-3V can be used,
whereby the exact value of the reference voltage is irrelevant, as this voltage is
then subtracted again. To do this, the reference voltage is applied to input A1 of
the ADC and A0 - A1 selected as the output.
Once the setup is complete, the measurement can be started and the amplification
factor selected with different masses so that a voltage is visible. The gain factor
here is A=18. While the measurement is in progress, pieces of weight up to
500 g are hung on the load cell in 50 g increments. In addition, the voltage is
taken up if no mass is attached.
The measured values are then exported and the stresses are assigned to the
respective attached masses. By averaging the voltage values over time during the
time when the respective piece of mass was attached, a voltage value can be
assigned to each mass. This results in ten voltage values for the ten pieces of
mass. It can be seen that the voltage is proportional to the attached
mass. The voltage that is measured without an attached mass is subtracted from
the other voltages as an offset voltage. After determining the compensation
function, this load cell can be used as a scale for masses of up to 500 g.
Fig. 37: The voltage of the load cell increases with increasing force. The
offset voltage that is applied without an attached mass is subtracted from the
remaining voltage values. The measured values are compatible with a straight line
through the origin.
The regression can either be carried out directly in PhyPiDAQ with the
ChanCalib function, or the values are exported and then transferred to Excel,
Python, etc. to be further processed.
Config:
kraftsensor.daq:
DeviceFile: config/kraft_ADS1115Config.yaml # 16 bit ADC, I2C bus
ChanLabels: ['Spannung'] # names for channels
ChanUnits: ['V'] # units for channels
ChanColors: [darkblue] # channel colours in display
Interval: 0.05 # logging interval
NHistoryPoints: 20000 # number of points used in history buffer, time=NHistoryPoints*Interval = 2000*0.05 = 100 seonds
DisplayModule: DataGraphs # text, bar-graph, history and xy-view
Title: "Data from File" # display title
DataFile: null # null to disable
CSVseparator: ' ' # field separator, set to ';' for German Excel kraft_ADS1115Config.yaml:
DAQModule: ADS1115Config
ADCChannels: [0]
DifModeChan: [true]
Gain: [1]
sampleRate: 860The photo effect is examined in more detail below. The resulting counter-voltage
should be measured for six different wavelengths in the range from λ = 360 nm to
λ=590 nm. Then the ratio h/e, where h is Planck's quantum and e is
the elementary charge, should be determined.
A mercury lamp is used as the light source because it also emits light in the UV
range. The light beam is bundled with lenses and reduced to the respective
wavelength with interference filters. When the photons hit the cathode, electrons
are released and a positive excess charge is created on the initially neutrally
charged plate. If electrons hit the opposite anode, it is negatively charged. The
separation of charges between the anode and the cathode creates an increasing
electric field, which slows down further electrons that fly from the cathode to
the anode. In equilibrium, the breaking force is so great that even electrons
no longer arrive at the anode with maximum kinetic energy. The voltage between the
cathode and anode is then maximum. The maximum voltage then corresponds to the
counter voltage.
The measuring method used here contains a capacitor connected in parallel to the
photocell, which is charged by the photovoltage. The tension that arises
corresponds to the counter-tension. This method has the advantage that a rather
complex and laborious setting of the photocurrent can be dispensed with. As a
result, this test can be carried out in a very short time and with high accuracy.
On the hardware side, the voltage is measured with the electrometer, since a large
internal resistance is required here in order not to falsify the measurement. A
commercially available multimeter is therefore unsuitable. The circuit structure
can be seen in the following figure:
Fig. 38: Photoeffect schematic structure
The capacitor with C=47µF may have to be adjusted if the charging is too fast
or too slow.
The following config can be used in PhyPiDAQ. (The plots below were created by
exporting the values from PhyPiDAQ as .csv and then reading them into a
Python script. This can be done just as well for the intermediate level, for
example, with an Excel table or something similar.)
photoeffekt.daq:
DeviceFile: config/photoeffekt_ADS1115Config.yaml # 16 bit ADC, I2C bus
ChanLabels: ['Voltage'] # names for channels
ChanUnits: ['V'] # units for channels
ChanColors: [darkblue] # channel colours in display
Interval: 0.05 # logging interval
NHistoryPoints: 20000 # number of points used in history buffer, time=NHistoryPoints*Interval = 2000*0.05 = 100 seonds
DisplayModule: DataGraphs # text, bar-graph, history and xy-view
Title: "Data from File" # display title
DataFile: null # null to disable
CSVseparator: ' ' # field separator, set to ';' for German Excel photoeffekt_ADS1115Config.yaml:
DAQModule: ADS1115Config
ADCChannels: [0]
DifModeChan: [false]
Gain: [1]
sampleRate: 860The measurement can now be started and the counter voltage is displayed, which
results from the charging of the capacitor by the photo effect. The capacitor is
connected to ground again for discharging.
To calculate the ratio h/e, the energy balance is first drawn up. The
incident light with the wavelength λ has the frequency ν=λc and the
energy Elight=hν. After deducting the work function, the released
electrons have the kinetic energy Ekin=Elight-E_A. For the energy
of the electric field, Efield=Ue* applies, where U is the counter
voltage and e is the elementary charge. In the stationary case, the energy of
the electric field is the same as the kinetic energy, Efield=Ekin, so
that when inserted, U·e=hν−E_A results. For the voltage U,
U=h/eν+eA applies. The ratio h/e corresponds to the slope in the U-ν
diagram in the figure below. The y-axis intercept corresponds to the work
function E_A, with a negative sign indicating that this work has to be done.
The deviation of (h/e)measured from the literature value of
h/e=4.14·10^(−15) Js/C is 3.5%, which indicates a very precise measurement and the set
goal of measuring in the percentage range fulfilled. The work function for a
potassium cathode is E_A = 2.25 eV. The y-intercept corresponds to
|U| = 1. 97V. Since no other effects such as contact stresses are taken into account here,
the determination of the work function with this method is basically only possible
with greater uncertainties.
Although a detailed calculation is not carried out at this point and the y-axis
intercept is extrapolated far away from the fitted measured values, the magnitude
of the extrapolated work function still agrees well with the expected one. The
photocurrent can also be calculated from the capacitor charge in the figure below.
It can be seen that this is in the pico range. The current was smallest at 590 nm,
which is evident from the relatively slow charging.
Fig. 39: Photo effect Charging of a capacitor on a vacuum photocell for different wavelengths of the incident light
Fig. 40: Photoeffect Saturation voltage versus frequency of light. The slope of the straight line, obtained via linear regression, corresponds to the ratio h/e.
