Set Up a Raspberry Pi I2C Temperature Sensor
There are several temperature sensors that are available for your Raspberry Pi one of the most popular being the DS18B20, however, if you are looking for an I2C connected temperature sensor then the Atlas Scientific RTD Temperature sensor is an excellent option. If your project already involves the use of other I2C sensors then this can be easily added in parallel without using any additional GPIO pins on your Pi. This sensor also provides onboard logging capabilities and provides readouts in either Celsius, Fahrenheit or Kelvin, with the addition of a thermowell you will be able to insert your temperature probe into your plumbing.
To configure the Pi I am assuming that you are running the latest version of Raspbian and have the ability to connect to your Pi either through SSH with putty and FTP with Filezilla or directly with a keyboard and monitor. If you haven’t set-up your Pi yet then check out my getting started section.
In this tutorial I will be using the following materials:
- Raspberry Pi (2, 3 or 4)
- Micro SD Card
- Power Supply
- Atlas Scientific Temperature Sensor Kit
- Jumper Wires
- Adafruit T-Cobbler Plus (Optional)
- Raspberry Pi Case (Optional)
The first thing we need to do is enable the I2C modules on the RPi. This is done by entering the following at the command prompt to start the configuration tool.
select option 9 – Advanced Options
select option A7 – I2C
select “Yes” for all the questions and reboot the RPi
After the reboot open the terminal and ensure that all the Raspbian packages are up to date, enter the following
Next, check/add the i2c tools package
This should produce the following without the sensor attached.
Now that we have our I2C module working correctly we can go ahead and connect our temperature sensor. When describing the physical pin connections I will be following the GPIO pin numbering convention shown below.
Firstly we need to get the temperature circuit into the correct mode, when delivered the temperature circuit will be in UART (serial) mode, the temperature circuit has to be manually switched from UART mode to I2C mode. When this is done the temperature circuit will have its I2C address set to 102 (0x66).
Using your breadboard perform the following actions
- Cut the power to the device
- Disconnect any jumper wires going from TX and RX to the Pi
- Short the PRB pin to the TX pin
- Power the device
- Wait for LED to change from Green to Blue
- Remove the short from the probe pin to the TX pin
- Power cycle the device
The device is now I2C mode.
The Pi and temperature circuit are now configured so we can go ahead and connect it all together
Assuming that all of the parts are now mounted on your breadboard
- Connect the GND pin of the temperature circuit to the ground pin of your RPi.
- Connect the TX(SDA) pin to GPIO pin 2.
- Connect the RX(SCL) pin to GPIO pin 3.
- The PRB and PGND pins should be connected via your breadboard to the center and shield pins of your BNC connector.
- Finally, power your temperature circuit by connecting the Vcc pin to the +3.3V pin.
You can now run a quick test to prove that we are set up correctly, from the command prompt enter the following:
you should see the following response, if not then check your connections, ensure the light on the temperature circuit is blue and reboot your Pi.
In the image above I have 4 sensors connected to my Pi, the Temperature sensor connection is indicated by Hex value 66. The factory preset address for the pH sensor is 102 or 66 in hexadecimal as mentioned above, if you have more than 1 temperature circuit connected then you will need to specify a different value. To do this we need to add some python code to our Pi.
Atlas Scientific provides the python code that I will be using here for interfacing with the temperature circuit.
We start by importing the required python modules
Next, we add the class code to interface with the temperature circuit (or any other Atlas Scientific circuit for that matter)