Open design of a fixed probe for water quality monitoring in rivers and lakes

This is the repository containing all the code and instructions necessary to build and run your own probe for water monitoring.

This work has been done by Nils Bonfils for his Bachelor project at EPFL and is supervised by Robin Scheibler and Sachiko Hirosue.

This project takes part in a wider one, the Biodesign project. It was done within the LCAV lab at EPFL and sponsored by it. The Hackuarium bio-hackerspace also provided tools and a place to work.

Is this for me ?

You just need to have some DIY skills, for scrapping some materials, figuring out how to assemble some things together and figuring out how some components work. The instructions given here should also be taken more like guidelines based on what I could do with the materials I had. So it is not required that you have the exact same sensors or else, they'll surely work a little different, but as they should do the same things, there will be similarities too.

You'll also need motivation and good will ! :)

Feel free to contact me if you manage to get it working with different components, so these instructions can be improved and be more helpful.

The probe

The core of the probe is a Raspberry Pi which will control the sensors and handle the collect of the data, then store/send it.

All the code in this repo was done on a raspberry pi under raspbian jessie lite. The only compatibility issue with other OS might be the systemd units (.service files). Otherwise its python3 code and it should work anywhere where python3 is installed.

The sensors

The sensors connected to the Raspberry Pi are :

• Turbidity sensor

  To measure the clarity of the water, see on Wikipedia.

  The sensor itself is a basic three pin (VIN, DATA, GND) turbidity sensor, like you can found in dishwashers. (Mine was bought for 2$ on AliExpress)

  This is an analog sensor and the Raspberry Pi hasn't a built-in analog-digital converter, you'll need an external one like the MCP3008 which works fine for that.

• Waterproof temperature sensor

  To measure the temperature of the water.

  The sensor is a Waterproof DS18b.

• Air temperature and barometric pressure sensor

  To measure the ambient temperature as well as the pressure, to have a clue on the weather.

  The sensor is a BMP180 from Adafruit.

• Capturing images

  To take images of the water and have some visual feedback.

  A basic usb web-cam can be used. (I used a LogiLink web-cam)

Data collection

The Raspberry Pi handles the sensors and gets the data from them, and then the data has three possible ways to go.

1. Network is available

   The data will be sent through the GPRS with the HTTP protocol via the GET method to a server, which then can parse, process and even display the data with a web interface. The image are sent via the PUT method.

2. No network but a USB drive is plugged in

   The data are stored on the USB root directory in the CSV format in a file named sensors_data.csv. The images taken by the web-cam are store in a directory named probe_img in the root directory of the USB and the images are called YYYYMMDDHHMMSS.jpg according to the time they were taken.

3. No network, no USB

   Everything is stored locally on the SD card of the Raspberry PI, thus being the file system of the OS that runs the Raspberry Pi. The data are stored in /srv/sensors/sensors_data.csv and the images in /srv/sensors/probe_img/.

The data collection system works by level. This means that when the first level is available everything will be done that way, otherwise it will use the second way, and the worst is the third. And as soon as a higher level is available things are "transfered" to this level. For example data are stored locally (3), but when an USB drive is available (2) everything will be dumped to it, and if it was network (1) everything that has been stored, since the network was unavailable, will be sent to the server.

The communication with the network is done by the use of a GSM/GPRS module connected with the serial GPIO pins of the Raspberry Pi which communicate with the legacy AT commands language. (The one I used is a GSM Click module)

Battery and power management

The Raspberry Pi on its own needs ~700mA, so using a Lipo Rider Pro which can output up to 1A seems a reasonable choice. The Lipo Rider Pro is used along with a battery and a solar panel, so the probe can sustain longer on its own.

Also a Witty Pi can be used to improve even further the sustainability of the probe. The Witty Pi is an extension module that will be used on the Raspberry Pi in order to shut it down to spare battery and to wake it up when there is a need to get/store/send data.

Other components

Other components that are used for the probe that are non electronic although essential.

• Two boxes

  One big that'll contains the raspberry pi and what's connected to it, and a smaller box for the BMP180, I highly recommend the big box to be waterproof IP66/IP67 so the electronics inside won't be damaged as the probe should be setup up near water. The smaller one needs some air to pass inside in order for the temperature and pressure measure to be correct, doing tiny holes in it is ok, but the holes needs to be protected so water can't drip in (rain, etc...).

• Some cables

  To connects the sensors to the Raspberry Pi and in order for the sensors to reach the water cables should be long enough (2-4m seems ok). The can also be used to link the two boxes. I recommend using cables with 4 wires.

• Some cable clamp

  For the cables of the sensors can exits the boxes without breaking the impermeability.

Usage

Once built and set up, the usage of the probe is trivial.

You install it near a river of lake, possibly somewhere stable, so the probe don't fall or tip because of the wind, and hidden, so it don't get stolen. Temperature and turbidity sensors goes in the water, power up the Raspberry Pi and then data should collected every 10 min and sent to a server or stored on a USB drive.

I suggest to run some tests before setting it up to see if the behaviour is as expected.

Instructions to set up and build the probe

It will be separated into two parts, the setting up and installations of software on the Raspberry Pi and the hook up of the circuits. The building part is left up to you as the boxes you may have chosen could differ a lot there are no real instructions to make holes in boxes and finding a way to fit everything in there, just try to keep everything as waterproof as possible.

The Raspberry Pi

At the very first what you want is to install a distribution on your Raspberry Pi, it's strongly suggested to download the iso of Raspbian Jessie Lite. Then you'll just have to follow the instructions related to your system on this page.

Once your SD card is good to go plug it in the raspberry and power it up. The default login and password are :

Login : pi

Password : raspberry

After that I recommend you to change the default password with the following command

passwd

Enter the current password (should be "raspberry") and then the new one. Now you'll need to install new software. In order to do that, you'll need to update the system first :

sudo apt-get update
sudo apt-get upgrade

This can take a little while, once done we can proceed with the installations. I will here just give the commands to enter as I will not enter into detailed explanations here. If you want to know more about what you're doing, take a look at some Adafruit guides :

• Raspberry Pi setup
• BMP180 setup
• DS18B setup
• MCP3008 setup

sudo apt-get install git python3-dev python3-rpi.gpio python3-smbus i2c-tools build-essential python3-setuptools python3-w1thermsensor fswebcam python3-udiskie
git clone https://github.com/adafruit/Adafruit_Python_BMP.git
cd Adafruit_Python_BMP
sudo python3 setup.py install

After that you'll need to configure some things manually, like kernel support for I2C as well as for the DS18B.

sudo nano /etc/modules

And add these two lines at the end of the file :

i2c-bcm2708
i2c-dev

Then you'll also need to comment some lines (put a '#' in front) if they exists :

sudo nano /etc/modprobe.d/raspi-blacklist.conf

And those two lines are :

blacklist spi-bcm2708
blacklist i2c-bcm2708

And finally, modify /boot/config.txt.

sudo nano /boot/config.txt

Add these lines at the end :

# Enable use of BMP180 sensor
dtparam=i2c_arm=on
dtparam=i2c1=on

# Enable use of DS18B sensor
dtoverlay=w1-gpio

Once everything is done, reboot !

sudo reboot

Last thing to do after the reboot, to finish the sensors configuration.

sudo modprobe w1-gpio
sudo modprobe w1-therm

So now the Raspberry Pi is ready to get all the sensors working. The last thing to do is to set up the server. Clone this repository first.

git clone https://github.com/nbonfils/fixed-probe.git

Setup the systemd service so the server start when the Raspberry Pi is powered up.

cd /etc/systemd/system
sudo ln -s /home/pi/fixed-probe/sensor-server.service
sudo ln -s /home/pi/fixed-probe/usb-hotplug.service
cd /usr/local/bin
sudo ln -s /home/pi/fixed-probe/sensor-server.py
sudo systemctl enable sensor-server.service
sudo systemctl enable usb-hotplug.service

And at the next startup the server will be running and collect data from sensors. If at any time you want to stop or start the server you can just use the following commands :

sudo systemctl stop sensor-server.service
sudo systemctl start sensor-server.service

And that's it, the Raspberry PI is configured and ready to run. You still need to hook up the circuits and build the probe.

Circuits hook up

Here will be presented the hook up of the different components separately.

Depending on the Raspberry Pi model there are more or less pins, but the layout of the pins are the same for the pins we are going to use. Here is the layout :

BMP180

It's really easy, just connect the following pins together :

BMP180	RPi
VIN	3.3V
GND	GND
SCL	SCL
SDA	SDA

Here is the schema from Adafruit tutorial :

DS18B

For this one you'll need a 10k Ohms resistor.

DS18B	RPi
VIN	3.3V
DATA	#4
GND	GND

The resistor should link the DATA and the VIN as in the following schema (from Adafruit) :

MCP3008 with turbidity sensor

Here you'll need a 10k Ohms resistor too. The hook up is slightly more complicated.

The pinout of the MCP3008 :

If you hook this up just as follows, everything should work fine.

MCP3008	RPi
VDD	3.3V
VREF	3.3V
AGND	GND
CLK	#18
DOUT	#23
DIN	#24
CS/SHDN	#25
DGND	GND

That's for connecting the adc to the Raspberry Pi, then to connect the turbidity sensor to the adc, just hook it up like this :

Sensor	MCP3008	RPi
VIN	X	3.3V
DATA	CH0	X
GND	X	GND

Along with that the 10k resistor should be installed between the DATA and the GND.

GSM module

The last module to hook up is the GSM module and as it's supposed to be used as a serial device, it's fairly simple.

GSM	RPi
VIN	3.3V
GND	GND
TX	RXD
RX	TXD

And that's it, everything should be hooked up, and if you launch the server, everything should work fine. The sensors_data.csv should fill up with actual data. The last thing to do if not already done is building the frame of the probe and fitting everything in.

Bachelor project

If you want to know more about how I've built such a probe myself, or if you're just curious to learn more about this project, I invite you to go check the wiki page of this project.

Also If you're interested in other Bio-tech stuff, I strongly recommend you to visit the Biodesign blog along with its wiki.