I2C stands for Inter-Integrated Circuit, pronounced eye-squared-C, and alternatively known as IIC. It is a synchronous, multi-controller/multi-target (controller/target), packet switched, single-ended, serial communication bus. This protocol is suitable for devices wired at short distances, no more than 2-3m. We use I2C in pretty much all our open source products: Internet of Things, mechanical keyboards and Raspberry Pi HATs.
I2C was originally developed in 1982 by Philips. While that makes it 40 years old, it is still a very convenient and widely used bus. There are many I2C sensors and peripherals. It is in pretty much every smartphone, embedded electronics, microcontroller, personal computer and of course Raspberry Pi.
Actually, since the introduction of the famous 40-pin header in 2014, Raspberry Pi single board computers have not one but two I2C buses! We use them both on ANAVI Info uHAT and our other HATs. Th first I2C bus is on pins 3 and 5. On the ANAVI Info uHAT, it is used for the three I2C slots for sensors and the 4th dedicated slot for the mini OLED display.
The second I2C bus is on pins 27 and 28 of the Raspberry Pi and is reserved exclusively for attaching an ID EEPROM. The ID EEPROM contains a software description of the hardware so the operating system on your Raspberry Pi can automatically identify the add-on board.
The I2C bus consists of two signals: SDA (Serial Data) is a data signal, SCL (Serial Clock) is a clock signal. I2C modules also need power, so the dedicated I2C connectors on the ANAVI Info uHAT and our other open source hardware provide two additional pins for VCC and GND. Typically, the VCC for the I2C connectors on our add-on boards for Raspberry Pi are 3.3V.
The I2C bus drivers are “open drain”, which means they can only pull the corresponding signal line at low level. They cannot drive it high. To restore the signal to high when no device is asserting it low, a pull-up resistor has to be added to each signal line. For example, on the ANAVI Info uHAT, we have 4.7K pull-up resistors R4 and R5 connected to SDA and SCL.
Resistor selection varies depending on the devices attached to the bus. In some specific use cases, further adjustment of the resistance value might be required. For systems with lots of devices or longer wires, smaller resistors are better.
How to Enable I2C on Raspberry Pi OS
Raspberry Pi OS, previously known as Raspbian, is the default and recommended Linux distribution for all models and versions of the Raspberry Pi single board computer. By default, I2C is not enabled. There are several ways to enable it, but probably the easiest is using the command-line tool raspi-config to perform few basic commands:
Open a terminal or login remotely via SSH to your Raspberry Pi and type in the following command: sudo raspi-config
Each I2C device must have a unique address. The I2C reference design has a 7-bit address space, although rarely it might be used with a 10-bit extension. The 7-bit addresses range from 0 to 127 (0 to 0x7F hexadecimal). This is a limitation because it is not possible to have two I2C devices with the same address on the same I2C bus. For example, the I2C address on the mini OLED display included in all ANAVI Info uHAT kits is 0x3C. From the software side, this address is used in the example Python 3 script to access the display.
For Linux distributions, including Raspberry Pi OS, there is a package with a heterogeneous set of I2C tools called i2c-tools. To install it on Raspberry Pi OS, open a terminal and execute: sudo apt install -y i2c-tools. Once you have it installed, you can list attached I2C devices by their addresses with i2cdetect. For example, if the HTU21 temperature and humidity sensor module is attached to the Raspberry Pi, the output will be:
OSHWA runs the certification program ensures that the definition of “open source hardware” used by a specific project matches the community’s definition of open source hardware. They provide a unique indentification (UID) for each version of the certified hardware based on the country code and a serial number. For example, the UID for ANAVI Info uHAT is BG000081. The prefix BG is the country code for Bulgaria, because the Info uHAT is made in my hometown of Plovdiv. The serial numbers show that now there are 81 open source hardware devices from Bulgaria.
MH-Z19B is an intelligent infrared CO2 module which interacts with the Raspberry Pi using UART (universal asynchronous receiver-transmitter). Takuya uses the UART port on ANAVI Infrared pHAT to attach MH-Z19B. The rest of the sensor modules for his setup are included in ANAVI Infrared pHAT Advanced kit: HTU21D for temperature and humidity, BMP180 for barometric pressure and BH1750 for light.
By the way, initially we had published open source examples for using HTU21D, BMP180 and BH1750 in the C programming languages using the library wiringpi. Takuya also based his setup on wiringpi. However, wiringpi is now deprecated therefore we have replaced it with another library called libi2c-dev. Furthermore we added examples written in Python 3.
We have good news regarding ANAVI Gardening uHAT! All boards have been received almost fully assembled from the local factory and we have sourced all required peripherals.
Recently, we received the last batch of assembled printed circuit boards from the local factory. As you can see on the photo, only the EEPROM is missing. We will flash and solder it in-house.
We have also received additional peripherals, which will be included in ANAVI Gardening uHAT Starter, Advanced, and Developer kits. On the photo you can see the big packages with analog capacitive soil moisture sensor. Each kit will contain a couple of capacitive soil moisture sensors.
The recyclable cardboard boxes for our eco-friendly packaging have also already been delivered. Another local company here in Plovdiv, Bulgaria will print all stickers for us. We expect them next week.
ANAVI Gardening uHAT is a low-cost, open source Raspberry Pi add-on board that helps you develop smart solutions for monitoring and growing plants.
ANAVI Gardening uHAT supports multiple sensors for soil moisture, temperature, humidity, barometric pressure, and light. Getting started is easy: just plug it into a Raspberry Pi with your bare hands and follow the instructions in the user manual. No soldering is necessary, and no tools are required.
Raspberry Pi is a famous series of small single-board computers (SBCs) developed in the United Kingdom by the Raspberry Pi Foundation in cooperation with Broadcom. This is a step by step tutorial for using Raspberry Pi and capacitive soil moisture sensor with Microchip MCP3002 analog-to-digital converter (ADC) and a Python script for detecting the soil moisture in percentage.
Capacitive Soil Moisture Sensor
Capacitive Soil Moisture Sensor v1.2 and v2.0 measures the volumetric content of water inside the soil and retrieves the moisture level by capacitive sensing rather than resistive sensing like other sensors. The benefit of using a capacitive soil moisture sensor is the lack of corrosion and longer lifespan.
Unlike Raspberry Pi Pico, the recently released microcontroller, all versions and models of the Raspberry Pi single-board computers do not include an analog-to-digital converter (ADC). This tutorial explains how to use Microchip MCP3002 with Raspberry Pi.
Microchip MCP3002 is a 10-bit resolution, dual channel ADC with SPI hardware bus. It can be connected to any Raspberry Pi single board computer version and model, including Raspberry Pi 4 and Raspberry Pi 0. However, this tutorial is not for Raspberry Pi Pico microcontroller. For more details about the wiring of Microchip MCP3002 a Raspberry Pi single-board computer have a look at my previous tutorial.
Alternatively, the easier option without a breadboard an a bunch of cables, is to use a dedicated Raspberry Pi add-on board with built-in ADC. Using the free and open source tool KiCad we designed ANAVI Gardening uHAT exactly for this purpose. It has dedicated pins for connecting a couple of capacitive soil moisture sensors. The prototype has been created thanks to PCBWay. This is a lead-free prototype printed circuit board with 2 layers, green solder mask and white silkscreen. PCBway offers a huge variety of colors and even flexible PCB.
Flash Raspberry Pi OS, the official Debian based GNU Linux distribution by the Raspberry Pi, on microSD card and boot it. On the Raspberry Pi, open a terminal and using the raspi-config tool enable SPI as shown in the video. Reboot the Raspberry Pi.
Python3 script for reading data from a couple of capacitive soil moisture sensors through Microchip MCP3002 ADC is available at the anavi-examples repository in GitHub. The script relies on popular Python libraries spidev and RPi.GPIO. Open a terminal and run the following commands to clone anavi-examples and run the script:
git clone https://github.com/AnaviTechnology/anavi-examples.git
If you are reading this blog post, I am sure you are familiar with Raspberry Pi, the a series of small single-board computers (SBCs) developed in the United Kingdom by the Raspberry Pi Foundation in cooperation with Broadcom. Unlike the recently released microcontroller Raspberry Pi Pico, all versions and models of the Raspberry Pi Linux computers do not include an analog-to-digital converter (ADC). If you need to read data from an analog device such as a potentiometer, sound or soil moisture sensor the solution is to use an external ADC, for example Microchip MCP3002.
Microchip MCP3002 ADC
Microchip MCP3002 is a 10-bit resolution dual channel ADC with SPI hardware interface for connecting to embedded devices such as Raspberry Pi. MCP3002 operates over a broad voltage range, from 2.7V to 5.5V. It is offered in 8-pin MSOP, PDIP, TSSOP and 150 mil SOIC packages. MCP3002 PDIP package is appropriate for prototyping on a breadboard.
Raspberry Pi and Microchip MCP3002 Wiring
Microchip MCP3002 has to be connected to the dedicated SPI pins (MISO, MOSI, SCL and SS) on the Raspberry Pi GPIO header. In the video a 10K potentiometer is connected to one of the two channels of the ADC for testing purposes. The potentiometer as well as Microchip MCP3002 are powered with 5V from the Raspberry Pi.
Boot Raspberry Pi OS, the official Debian based GNU Linux distribution by the Raspberry Pi, from a microSD card. Open a terminal and using the raspi-config tool enable SPI as shown in the video. After that reboot the Raspberry Pi and proceed to the next step.
Reading Data with Python
Python3 script for reading data from analog devices through MCP3002 is available at the rpi-examples repository in GitHub. The script relies on popular Python package RPi.GPIO. Open a terminal and run the following commands to clone rpi-example and run the script:
git clone https://github.com/leon-anavi/rpi-examples.git
The potentiometer acts like a variable resistor. Rotate it and observe the output of the Python script. You will notice a change of the voltage between 0V and 5V depending on the position of the potentiometer.
ANAVI Garderning uHAT
Thanks to PCBway, the sponsor of this video, we can go to the next level and use a prototype of ANAVI Gardening uHAT as a Raspberry Pi add-on board with SOIC package of Microchip MCP3002. ANAVI Gardening uHAT follows the specifications of Raspberry Pi Foundation for HAT (hardware attached on top), including for an EEPROM with device-tree binary overlay configurations.
Jesús has attached various sensors for collecting data as we as a Raspberry Pi camera to take pictures of the room. He has developed energy efficiency algorithms running in the cloud which make decisions based on the data from the sensor and after that ANAVI Infrared pHAT takes care for transmitting commands as a stream of infrared signals to his air conditioner.
This step by step tutorial explains how to install and configure the free and open source video conference software Jitsi Meet on Raspberry Pi with 64-bit Ubuntu Server 20.04. Although the Jitsi Meet installation is simple, the network configuration is not.
This tutorial is only for 64-bit Raspberry Pi models and versions, for example Raspberry Pi 4 or 3. It is recommended to use Raspberry Pi 4 with 4GB or more. Please note that Raspberry Pi 0, 2 and other older versions are 32-bit and this tutorial is NOT suitable for them.
To successfully run self-hosted Jitsi Meet on your Raspberry Pi at home and allow your friends and family to access it from anywhere you need to make several network configurations.
The network setup depends on your WiFi router and although the steps in general are the same they vary depending on the router model and version:
Dynamic DNS (DDNS) – the public IP of your WiFi router is provided by your ISP (Internet Service Provider) and in general may change over time. To avoid service downtime and hassle to remember IP address, it is highly recommended to setup DDNS. Some ASUS routers, like RT-AC68U, have this advanced service built-in. Alternatively you can use one of the many free or low-cost DDNS services.
SSL (Secure Sockets Layer) certificate – for secure communication over HTTPS. It is highly recommended to get a free certificate from the automated and open certificate authority Let’s Encrypt. You can do this through your WiFi router (if it supports it), manually or during the installation of Jitsi Meet.
Port Forwarding – two ports must be forwarded from the Raspberry Pi on which Jitsi Meet is running to the Internet through the configurations of the WiFi router. By default these ports are: 443/TCP for the HTTPS server and 10000/UDP for the video bridge of Jitsi Meet.
Install Jitsi Meet
Download and add Jitsi GPG key to the list of trusted keys. Once added you can remove the downloaded file.