"Meteobike" is our educational Raspberry Pi Zero Project at the University of Freiburg, Chair of Environmental Meteorology. In our course "Tools in Meteorology" (5th Term of our Minor in "Meteorology and Climatology"), we develop a system to measure, analyze and visualize the urban heat island effect. Within a short period (~2 hours), we measure with many systems simultaneously temperature and humidity transcects inside and outside the city and tag measurement locations with GPS. The system is battery operated and light, so it can be mounted on bikes. Communication with the Raspberry Pi Zero to our smartphone is enabled via wireless network.
Students build their own mobile system.s Each system will be assembled using the following components:
| Component | Model | Link to Vendor in Germany | Price |
|---|---|---|---|
| Microcontroller | Raspberry Pi Zero W | Pimoroni.de | 10 EUR |
| GPS | Adafruit Ultimate GPS Breakout | Pimoroni.de | 40 EUR |
| Temperature / Humidity Sensor | DHT22 AM2302 | AZ-Delivery (Amazon.de) | 5 EUR |
| Micro SD Card | NOOBS 16GB microSD | Pimoroni.de | 5 EUR |
| Battery | POWERADD Pilot 2GS Powerbank 10000mAh* | Poweradd (Amazon.de) | 15 EUR |
| Jumper Wires | Elegoo Jumper Wire* | GYE (Amazon.de) | 7 EUR |
- Can be replaced by any other product
The Raspberry Pi Zero W is a microcomputer running a full operating system and providing input and output connectivity through a number of interfaces:
Your Raspberry Pi Zero W comes with a micro SD cards with the operating sysetm (called Raspbian) preinstalled. The micro SD card is inside the larger regular SD card "adapter". Pull the micro-SD card out and insert it carefully into the card slot. Make sure the logo is up and the hand-painted white number on the back.
The first time you set-up your Raspberry Pi Zero W, you will need a few additional components. Those components can be used for setting-up multiple systems in a row. The components you need are
- Screen (HDMI or VGA)
- USB keyboard
- USB mouse
- A USB hub
- Various interface cables.
In our course, you share a screen, a keyboard and a mouse, and connection cables between two students each.
Later, once the system is assigned to your wireless networks, you can connect to it without keybord, without mouse and without Screen using RealVNC, so there is no need for a phsyical keyboard, a mouse or a screen during the bike traverses. All can be controlled on your smartphone or tablet, or just be operated remotely.
Here are all connection cables and supplies you need for the initial set-up (screen is not shown):
To connect the screen during the initial set-up, connect the mini-HDMI cable to you screen (possibly using a HDMI to VGA adapter if your screen does not support HDMI and only VGA):
Next, connect the USB ports. Your Raspberry Pi Zero W has two mini-USB ports, one (left) is for the USB devices (mouse, keyboard), one (right) is actually only for supplying power. First connect to the USB devices (left). Because there is only one true USB port, but you need to connect two devices, you must also add initially a USB hub. Here is the set-up:
Finally connect the power supply to the right mini USB connector. The Raspberry Pi Zero W now starts up, the green inicator light begins to flash, and instructions follow on your screen.
Follow the instructions on-screen to set-up your Raspberry Pi Zero W. It will automatically reboot after resizing.
Then connect to the wireless network. Click in the menu-bar on the wireless network icon, select our network and enter the password. Details on the password and network can be found on your desk. Hover with the mouse over the network icon to read the IP number. Note the IP number on your sheet on the desk.
Next, localize the Raspberry Pi Zero W to your language and region. Provide a password to the Raspberry. Set the same password as the wireless network, so we have all the same password. Make sure it starts with a capital letter. Also change the Hostname to "raspberryXX" where XX is the number of your system (see sheet on your table):
Test the communication with another device (your laptop or smartphone). First activate VNC. Go to settings, and enable "VNC". You can also enable SSH und I2C.
Next, on your laptop or smartphone install the "VNC Viewer" from "RealVNC":
- On Mac, Windows, or Linux install the desktop version of the VNC Viewer.
- On iOS devices use the Apple App Store to download the VNC Viewer.
- On Android devices use Google Play to download the VNC Viewer.
Make sure your laptop or smartphone is connected to the same wireless as the Raspberry Pi Zero W. Then start your viewer, connect to the IP address you previously noted (likely 192.168.X.Y) and enter the username "pi" with the password we have previously set.
You should be able to control your Raspberry Pi Zero W and you can use a mouse and keybord remotely.
The DHT22 is a low-cost digital temperature and humidity sensor. It contains a capacitive humidity sensor and a thermistor (resistor that changes with temperature). It transfers data digitally to your Raspberry Pi Zero W. You need just three cables to connect the DHT22 to the Raspberry Pi Zero W - one for power (red), one for the signal (orange) and one for the ground (brown).
To enable communication with the DHT22 , enter the following commands once into the LXTerminal (the command line) on the Raspberry Pi Zero to install the Adafruit DHT 22 library. Once the library is installed, you can access it from the programming language Python.
$ sudo apt-get update
$ sudo apt-get install build-essential python-dev python-openssl git
$ git clone https://github.com/adafruit/Adafruit_Python_DHT.git
$ cd Adafruit_Python_DHT
$ sudo python setup.py install
Next, turn off the Raspberry Pi Zero. Disconnect the power cable from the Raspberry Pi Zero. Connect the DHT22 sensor physically using the pre-soldered wires, with the following color coding on the pins of the Raspberry Pi Zero:
| DHT22 T/RH Sensor | Cable Color | Raspberry Pi Zero |
|---|---|---|
| PIN 1 | Red Cable | PIN 1 (3V+) |
| PIN 2 | Orange Cable | PIN 7 (GPIO4) |
| PIN 3 | (no cable) | |
| PIN 4 | Brown Cable | PIN 9 (Ground) |
Double check if the connection is correct. A wrong connection could damage the sensor and or the Raspberry Pi Zero. Then reconnect the power cable to the Raspberry Pi Zero. The Raspberry Pi Zero restarts, and its green light flashes.
Once started, the DHT 22 Sensor can be polled with the following commands in Python. First start the Phython development environment for Python 2.7 in interactive mode. In Python, enter
>>> import Adafruit_DHT
>>> humidity, temperature = Adafruit_DHT.read_retry(Adafruit_DHT.DHT22,4)
>>> print temperature, humidity
This will display the currently measured values. The system measures temperature and humidity every two seconds.
Next, as an exercise you can calculate the vapour pressure using the Clausius-Clapeyron equation. First calculate the saturation vapour pressure in kPa, then convert the relative humidity to vapour pressure. Note that temperature needs to be converted to Kelvins first.
>>> import numpy
>>> saturation_vappress = 0.6113 * numpy.exp((2501000.0/461.5)*((1.0/273.15)-(1.0/(temperature+273.15))))
>>> vappress=(humidity/100.0)*saturation_vappress
>>> print vappress
Can you also calculate the dewpoint temperature?
The Adafruit Ultimate GPS is a 66 channel Global Positioning System using satellites to accurately determine your location, speed and altitude. It digitally communicates with the Raspberry Pi Zero W over four cables:
To enable communication with the Raspberry Pi Zero W, start the Raspberry's LXTerminal and type:
$ sudo apt-get install gpsd gpsd-clients python-gps
$ sudo systemctl stop [email protected]
$ sudo systemctl disable [email protected]
$ sudo systemctl stop gpsd.socket
$ sudo systemctl disable gpsd.socket
For the Raspberry Pi Zero we need to enable the serial port on the GPIO pins. This requires us to change the configuration file of the Raspberry Pi Zero W. You can use a texteditor, for example the nano command in LXTerminal and edit the file config.txt
$ sudo nano /boot/config.txt
Scroll to the the very bottom of the file (not with a mouse, but with the arrow keys) and then type this on a new line:
enable_uart=1
Save with Ctrl+0 (German: Strg+O), and then press Enter. Next press Ctrl+X (Strg+X) to exit the nano editor. Finally, reboot the Raspberry Pi Zero.
Once rebooted, disable the standard socket, and run this command in the LXTerminal to enable the serial port:
$ sudo gpsd /dev/ttyS0 -F /var/run/gpsd.sock
Next, edit the file /etc/rc.local, again using the nano editor:
$ sudo nano /etc/rc.local
An insert at the very end, but above the line exit 0 the following line:
gpsd /dev/ttyS0 -F /var/run/gpsd.sock
Save with Ctrl+0 (German: Strg+O), and then press Enter. Next press Ctrl+X (Strg+X) to exit the nano command line editor.
Now, every time the Raspberry Pi Zero is booted, this command will be executed.
Turn off the Raspberry Pi Zero. Disconnect the power cable from the Raspberry Pi Zero. Connect the GPS physically using the pre-soldered four wires, with the following color coding on the pins of the Raspberry Pi Zero:
| GPS | Cable Color | Raspberry Pi Zero |
|---|---|---|
| PVIN | Black Cable | PIN 4 (5V+) |
| GND | White Cable | PIN 6 (Ground) |
| RX | Grey Cable | PIN 8 (TXD) |
| TX. | Purple Cable | PIN 10 (RXD) |
Double check if the connection is correct. Then reconnect the power cable to the Raspberry Pi Zero. The Raspberry Pi Zero restarts, and the green light flashes.
Now, you can test the GPS using:
$ cgps -s
Note: If the GPS is searching for a signal it will flash red 5 times in 10seconds and if it flashes red once in 15 seconds it has been connected to the satellites.
We want the data from the GPS and the DHT22 to be automatically collected and written into a file. We would also benefit from having the system data displayed in real time on screen. This is done with the python program meteobike03.py, which you can download on your Raspberry Pi Zero here:
You can start meteobike03.py using LXTerminal (assuming your file has been downloaded to the desktop)
$ python ~/Desktop/meteobike03.py
Next, make changes to personalize your copy of meteobike03.py. You can, for example, open the Python Development Environment (Version 2.7) and File > Open.
- Replace "01" on line 41
raspberryid =to your system#s two digit number. If your system has the number "7" enter "07". - Replace "andreas" on line 42
studentname =to your first name in quotes.
Then save the modified code File > Save. Close the Python Development Environment.
Every time meteobike03.py is started, it will create a new data-file that contains the data sampled. Here is an example:
| ID | Record | Raspberry_Time | GPS_Time | Altitude | Latitude | Longitude | Temperature | TemperatureRaw | RelHumidity | RelHumidityRaw | VapourPressure | VapourPressureRaw |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 01 | 8 | 2018-05-06 08:29:03 | 2018-05-06T06:29:04.000Z | 281.700 | 47.991855 | 7.845193 | 23.0 | 23.1 | 41.9 | 42.0 | 1.196 | 1.192 |
| 01 | 9 | 2018-05-06 08:29:11 | 2018-05-06T06:29:12.000Z | 288.000 | 47.991375 | 7.845212 | 22.9 | 23.0 | 41.9 | 42.0 | 1.188 | 1.185 |
| 01 | 10 | 2018-05-06 08:29:24 | 2018-05-06T06:29:25.000Z | 290.000 | 47.991242 | 7.845800 | 23.0 | 23.1 | 41.9 | 42.0 | 1.196 | 1.192 |
You can also place a link - called bash script on your desktop (meteobike.sh)
To ensure it works, you must change permissions of the file as follows (make it executable). This way, it can be started with a double-click:
$ chmod +x ~/Desktop/meteobike.sh
Now you can double-click meteobike.sh to start the user interface. Later, we will automate the start-up during the boot process.
You can enter the calibration coefficients we derived from the intercomparison directly into the python code. Open the file Meteobike03.py in the Python 2 editor on the Raspberry Pi Zero W and change the follwing four lines:
temperature_cal_a1 = 1.00000
temperature_cal_a0 = 0.00000
vappress_cal_a1 = 1.00000
vappress_cal_a0 = 0.00000
Replace the values 1.00000 and 0.00000 for temperature and vapour pressure based on the individual correction coefficients listed in . make sure you use a . and not a , as the delimiter.
Materials needed to complete the assembly of system include:
- Reflective Tape
- Scissors
- Sensor Screen/Radiation Shield
- Bag
- GPS/T&RH Sensor
- Velcro
- Screw & Bolt
- Foam
To begin the assembly of the Meteobike system, carefully cut the reflective tape to the length of the white plastic tube. Wrap the tube with the tape lengthwise, cut another piece of the same length and repeat this step with minimal overlap of the first piece of tape. The two pieces of tape should cover the entire tube.
Now that the tube is completely covered with the tape, use the scissors to puncture a hole in the tape where the holes on the tube are located. This is the sensor screen for the temperature and humitidy sensor.
To connect the temperature and humidity sensor to the radiation shield, you must disconnect the temperature and humidity sensor from the Raspberry Pi, please ensure the sensor is not connected to any source of power.
You will use the cirlce hook and loop velcro to attach the sheild and sensor. Place one piece on the inside of the radiaiton shield on the side that has 3 holes. It should be located close to the small hole that is farthest from the large hole. Place the second piece of velcro on the back side of the temperature and humidity sensor.
Pass the wires from the sensor through the shield and through the largest hole, then press the sensor to the shield and ensure the velcro will hold the sensor and shield together.
Place the shield close to the bag and put the temperature and humidity sensor wires through the large hole in the bag.
Now you must connect the radiation shield and the sensor to the bag. To do this, you will use a wrench and screwdriver to insert the bolt and screw through the shields two holes and through the hole that is on the bag.
Using the wrench to hold the bolt in place, use the screwdriver to insert the screw into the bolt to hold it secure. Place the thin plastic plate with the same holes on the inside of the bag apply the screw through it and the bolt on the inside.
You can now reconnect the the DHT22 sensor physically using the pre-soldered wires to the Raspberry Pi W.
| DHT22 T/RH Sensor | Cable Color | Raspberry Pi Zero |
|---|---|---|
| PIN 1 | Red Cable | PIN 1 (3V+) |
| PIN 2 | Orange Cable | PIN 7 (GPIO4) |
| PIN 3 | (no cable) | |
| PIN 4 | Brown Cable | PIN 9 (Ground) |
Please double check to make sure the connection is correct.
To ensure the protection of the sensor, a special foam is used. As you can see it is structured into cubical formation that allows you to remove the specific size and pattern you need.
You will be given a 20x28 cubical foam sheet, using this you will remove two 7x12 cube pieces, one will be for the base of your sensor and one will be altered to protect the Raspberry Pi system.
You should be able to remove 6 different 7x12 sheets from the original 20x28 sheet.
When sizing the foam for the Raspberry Pi, you will remove the foam cubes from the arrangement found below:
There is one location in the foam where you must use the scissors to remove only half of the cube. This is where the power cable will be guided and should be faced down in the bag.
You will now connect the battery and arrange the foam, battery and sensors to be comfortably situated within the bag.
The arrangement within the bag will consist of the battery at the base, followed with the unaltered foam, the cable for the battery, the altered foam and the Raspberry Pi within.
You must place the Raspberry Pi on top of the altered foam then connect the battery cable to the Raspberry Pi under the altered foam where you cut out the half cubes.
The GPS can be placed into the front pocket. Please make sure the antenna is facing up, this is to ensure a full connection with the satellites and a accurate track recorded.
When the system is complete, it should look similar to the image below.
Once the system is set up similar to what is arranged above, you can connect your mobile device to the VNC viewer in order to see the progress as you are collecting your data.
Place your mobile device in the front pocket behind the GPS.
In a first step, enable your phone to host a Personal Hotspot. Although you do not need to access the Internet and you will not use any of your data plan capacity, this is required in order to build a network over WiFi to communicate between the Raspberry and your Phone. However, make sure you do not browse the web or download any files while connected to your Personal Hotspot (otherwise charges will apply to your data plan). Also make sure you use a personal, not the course password to protect your connection.
Here is a description (in German) how to enable a personal hotsopt on your iOS smartphone
Here is a description (in German) how to enable a personal hotsopt on your Android smartphone
In both cases, you will now have a WiFi network enabled, and you can connect to the network from the Raspberry Pi Zero.
Boot the Raspberry Pi Zero, and then change the WiFi network to your Personal Hotspot WiFi name:
Enter your password when promted:
Then read the IP number (hover over the WiFi symbol in the menu bar to see it) e.g. 172.20.10.7 (without the "/", and what comes afterwards).
Go back to your phone and start the VNC app. In the VNC app create a new connection and enter the local IP number you just read, e.g. 172.20.10.7 (without the "/", and what comes afterwards). When connecting enter the username "pi" and the previously set VNC password. You should now be able to control your Raspberry Pi Zero as long as the phone and the raspberry are close together.
You can put the phone into the transparent lid of the bag. You can also use the second outlet of the power bank to keep your phone charged during measurements, but in this case, you must bring your own charger-cable.
Now you are ready to install the system on your bike.Let's go for a test drive. Make sure the indicator changes from red to yellow, as soon as you are outdoors. The recording will only start if you have a good GPS connection. Drive for about 15 - 20 minutes, and come back to our lab room.
The GPS track is stored by the Raspberry on the desktop as a comma-separated file.
If the Raspberry is in the same WLAN as the host computer, then you can easily establish an FTP connection and copy this file to the host (on the Mac, for example with "Cyberduck").
A first graphical representation of the track can be done place on the website http://www.gpsvisualizer.com/map_input
At top left choose "With: 1400", then at the top right under "Upload" choose your file and Click on Draw the map.
Color-coded drawing by temperature: Under "Track options" click on "advanced options" and make the following settings below:
Colorize by: custom field
Custom colorization field: temperature
Spectrum direction: down
Hue 1: 120
Hue 2: 0
Then click on Draw the map. Here is an example
There are also option to export it into Google Earth.
You can use the free and open-source Geographic Information System (GIS) QGIS to perform advanced geographical analysis, including statistics on specific areas of the track or rasterization of many Meteobike traces.
Check out the separate page on Visualizing Meteobike data wit QGIS...
