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Locally connected microcontrollers and real-time analytics (part 1 of 2)

Author(s): @lepistom ,   Published: 2018-08-31

Markku Lepisto | Solutions Architect | Google

Contributed by Google employees.

This two-part tutorial demonstrates how to use an Arduino Microcontroller to provide analog sensor readings to a Raspberry Pi, connect the devices to IoT Core, post telemetry data from the devices, and analyze the data in real time. Part 1 of the tutorial creates a 'hybrid' device, combining the strengths of a Linux-based microprocessor with internet connectivity and TLS stack, together with a constrained microcontroller for analog I/O. The devices act as a cloud-connected solar and wind power generator.

devices diagram

Part 1 objectives

  • Program the Arduino with the Sketch language.
  • Read analog sensor values.
  • Transmit the data over a serial connection to the Raspberry Pi.
  • Program the Pi in Python to read digital sensor values.
  • Post the combined analog and digital sensor data to IoT Core over a secure MQTT connection.

In part 2 of the tutorial, you will learn how to process, store, and analyze the streaming data in real time.

architecture diagram

Before you begin

This tutorial assumes you already have a Google Cloud account set up. You will also need to download and install the Arduino IDE on your local development environment.


This tutorial uses billable components of Google Cloud, including the following:

  • IoT Core
  • Pub/Sub

This tutorial should not generate any usage that would not be covered by the free tier, but you can use the Pricing Calculator to generate a cost estimate based on your projected production usage.

Required hardware

  • Raspberry Pi 3 Model B or B+. The instructions should work on other Pi models as well, but this has not been verified.
  • Raspberry Pi case (optional but recommended)
  • Raspberry Pi power supply, rated at 2.5A or more
  • MicroSD card for Raspberry Pi OS Lite. Minimum 8GB card recommended
  • Raspberry Pi Sense HAT add-on board
  • Arduino Uno Genuino or 100% compatible microcontroller
  • Two (recommended) analog sensors for the Arduino. In this tutorial we use a small solar panel and a small DC motor to generate analog voltage readings
  • USB type A to type B cable (to interconnect the Pi and Arduino)
  • USB keyboard
  • Monitor with HDMI input
  • HDMI cable

Create an IoT Core registry and device

First, execute all the steps in the IoT Core Quickstart on your local development environment e.g laptop. But do not clean up the environment. The rest of this tutorial will use the registry, device, and device keys created with the quickstart.

Raspberry Pi installation and configuration

Raspberry Pi OS Lite installation and configuration

  1. Follow the instructions here to download the latest Raspberry Pi OS Lite, and write it on your MicroSD card. All the steps in this tutorial run in console mode on the Pi, or over SSH to the Pi.
  2. Insert your Pi into the Pi case.
  3. Plug your Sense HAT into the Pi's 40-pin connector.
  4. Insert the MicroSD card into the Pi card slot.
  5. Connect the USB keyboard into the Pi.
  6. Connect the Pi to your monitor with the HDMI cable.
  7. Optionally, if you use Ethernet connectivity, connect your ethernet cable to the Pi.
  8. Connect the Pi power supply to the wall socket and to the Pi, to boot up Raspberry Pi OS Lite.
  9. Login to the Pi with the initial username: pi and password: raspberry
  10. Execute raspi-config as the superuser with:

    sudo raspi-config
  11. Change the pi user's password by selecting: 1 Change User Password

  12. If you are using Wi-fi, select: 2 Network Options then N2 Wi-fi to configure your Wi-fi country settings, SSID and passphrase.

  13. To get most console apps to display text correctly, select: 4 Localisation options then I1 Change Locale. Scroll down with the down arrow key, and deselect the default option (en_GB.UTF-8 UTF-8) using the space bar.

  14. Scroll down to en_US.UTF-8 UTF-8 and select that option with the space bar.

  15. Press Tabulator and select: Ok

  16. Use the arrow keys in the Configuring locales window to select en_US.UTF-8 from the list of choices as the default locale. Press Tabulator and select: Ok

  17. To set your system timezone, select: 4 Localisation options then I2 Change Timezone and use the menu options to find your geographic region and country. Setting the timezone is important because Google IoT Core requires client devices' system clocks to be within 10 minutes of real time. Raspberry Pi OS Lite uses global NTP time servers to synchronize the clock.

  18. Optionally, select: 4 Localisation options then I3 Change Keyboard Layout to match your layout. If you are not sure, select: Generic 105-key (Intl) PC, then English (US), then The default for the keyboard layout, then No compose key.

  19. Select: Interfacing Options, then P2 SSH, then Yes to enable the SSH server on your Pi.

  20. Select: Interfacing Options, then P5 I2C, then Yes to load the ARM I2C kernel module. The Raspberry Pi Sense HAT sensor module used in this tutorial uses I2C.

  21. Select: Finish, to exit the raspi-config tool and accept to restart the Pi. If you are not prompted to reboot when you exit raspi-config, reboot the Pi by executing:

    sudo reboot
  22. Log in as the pi user with your new custom password.

  23. Verify that you have an IP address on your Pi by executing:

    ifconfig -a

    You should see a client IP from your local network segment in either the wlan0 or eth0 interface.

  24. Verify that your DNS resolution and internet connection work, by executing:

    ping www.google.com
  25. If you do not have an IP address, or DNS resolution or internet connectivity fail, do not proceed further until you have fixed your Pi's network configuration.

  26. For Wi-fi connectivity only - check if your Wi-fi adapter has power saving enabled. We have to disable Wi-fi power saving, or it will give you sporadic network connectivity issues later on. Check the current state by executing:


    Look for "Power Management" under the wlan0 interface. If you see Power Management:on, then we have to disable it.

  27. On Pi 3 model B/B+, disable wlan0 Wi-fi power management by configuring /etc/network/interfaces. Execute:

    sudo vi /etc/network/interfaces

    or use the nano editor if you prefer. Add these lines to the end of the file:

    allow-hotplug wlan0
    iface wlan0 inet manual
        # disable wlan0 power saving
        post-up iw dev $IFACE set power_save off
  28. Reboot the Pi with:

    sudo reboot

    to apply the changes. Then log in again as the pi user.

  29. Execute:


    to ensure that Wi-fi power management is now: Power Management:off for wlan0.

  30. Execute:

    ping www.google.com

    to check your internet connectivity.

  31. Upgrade the Raspberry Pi OS Lite packages to latest versions with:

    sudo apt-get update && sudo apt-get upgrade -y

Install Cloud SDK and dependencies for Pi Sense HAT

  1. SSH to the Raspberry Pi with:

    ssh pi@YOUR_PI_IP
  2. On the Pi, follow all the steps here to install and initialize Cloud SDK for Debian systems.

  3. Check that Cloud SDK is installed and initialized with:

    gcloud info

    Ensure that the Account and Project properties are set correctly.

  4. Install Git, Python development packages and Sense HAT dependencies with:

    sudo apt-get update && sudo apt-get install -y git virtualenv python-dev sense-hat libffi-dev libssl-dev libopenjp2-7 libjpeg-dev

Clone the Pi client app and install its dependencies

  1. Using the SSH connection to the Pi, clone the repository associated with the community tutorials:

    git clone https://github.com/GoogleCloudPlatform/community.git
  2. Change to the tutorial directory:

  3. Create a Python virtual environment:

    virtualenv venv
  4. Activate the virtualenv:

    source venv/bin/activate
  5. Upgrade pip and setuptools:

    pip install -U pip setuptools
  6. Install the required Python modules:

    pip install -r requirements.txt
  7. Copy the private key file that you generated from IoT Core Quickstart guide to the app's current working directory on the Pi. Back on your laptop command line, you can use scp to transfer the file to the Pi, with for example:

    scp rsa_private.pem pi@YOUR_PI_IP:ardu-pi-serial/

You can check your Pi's IP address by executing:


on the Pi.

Arduino Uno installation and configuration

Connect the sensors to the Arduino

IoT boards and components boards diagram

  1. Connect 2 analog sensors to the Arduino. See the board diagram above to see how to wire the 2 sensors to the Arduino. In this example, we will read the analog voltage values of a DC motor, and a solar panel. You can replace the DC motor and solar panel with other analog sensors—but you have to ensure that the sensor output does not exceed 5V or it can damage the Arduino pin.*
  2. Connect the first sensor (small DC motor) to the Arduino. Connect the black ground wire of the motor to a GND port, and the red (voltage input/output) wire to port A0 on the Arduino.
  3. Connect the second sensor (small solar panel) to the Arduino. Connect the black ground wire of the panel to a GND port, and the red (voltage output) wire to port A1 on the Arduino.

Compile the Arduino Sketch

  1. Connect your Arduino to your local development machine with a USB cable. Note that the Arduino Uno board used as the example in this tutorial has a USB type B connector on the board. The USB cable will provide both power and serial data connectivity to the Arduino from your machine.
  2. Launch the Arduino IDE software on your local machine.
  3. Go to the Arduino menu bar, then Tools, then Board and select Arduino/Genuino Uno.
  4. Check the Port options under Tools and select the port on your computer that has Arduino/Genuino Uno visible and connected.
  5. Select File then New to open a new Sketch.
  6. Delete all the text in the new Sketch template.
  7. Copy and paste this code into your new Sketch:

    #define WINDGEN_PIN A0
    #define SOLARGEN_PIN A1
    String inputString = "";
    boolean stringComplete = false;
    int windgen = 0;
    int solargen = 0;
    char sendBuffer[32];
    char ch = 0;
    void setup() {
      pinMode(LED_BUILTIN, OUTPUT);
      digitalWrite(LED_BUILTIN, LOW);
    void loop(){
      if (Serial.available()) {
         ch = Serial.read();
         if ( ch == '0' ) {
    void sendTelemetry() {
      digitalWrite(LED_BUILTIN, HIGH);
      memset(sendBuffer, 0, sizeof(sendBuffer));
      int windgen = analogRead(WINDGEN_PIN);
      int solargen = analogRead(SOLARGEN_PIN);
      sprintf(sendBuffer, "S s:%d w:%d", solargen, windgen);
      digitalWrite(LED_BUILTIN, LOW);
  8. Select File then Save As... and save your sketch with a suitable name such as ardu-pi-serial.

Arduino IDE and Sketch Sketch diagram

Test reading Arduino sensors over serial connection from your machine

The Arduino Sketch client has the following functionality:

  • Check if the serial connection has data available to read
  • If the received character (command) is 0:
    • Read the voltage values of pins A0 and A1
    • Print the sensor values to the serial connection

Perform the following steps to deploy and test the Arduino sketch:

  1. Select Sketch then Verify/Compile from the Arduino IDE menu. If the code is successfully verified, the Arduino IDE should display Done compiling. You should also see output similar to the following:

    Sketch uses 4708 bytes (14%) of program storage space. Maximum is 32256 bytes.
    Global variables use 249 bytes (12%) of dynamic memory, leaving 1799 bytes for local variables. Maximum is 2048 bytes.
  2. Select Sketch then Upload to transfer the compiled Sketch to your Arduino over the USB serial connection. You should see the Arduino's LEDs blink rapidly while the binary is transferred over.

  3. Select Tools then Serial Monitor to open the Serial Monitor window.

  4. Ensure that the baud rate is set to "115200 baud".

  5. Test requesting the current sensor values from the Arduino, by typing 0 (zero) in the Serial Monitor's input window, and pressing Enter. If the Sketch and serial connection works, you should see a response similar to: S s:136 w:43 in the Serial Monitor.

Here, S indicates sensor output, s:136 is the current value of the solar panel (analog pin A1) and w:43 is the current value of the wind generator / DC motor (analog pin A0). This is how the Python client app on the Pi will request the sensor readings from the Arduino later on. Command 0 is an example of a simple protocol used to command an Arduino program.

Different inputs (e.g 1) could be used to command the Arduino to perform a different action, such as turning a servo motor. In this tutorial, the Arduino Sketch implements a single command 0, which reads the voltage values of analog pins A0 and A1.

  • Unplug the USB cable from your local machine to disconnect and power down the Arduino. The Arduino will now run the sketch automatically, whenever it is connected to a power source.

Connect the Arduino to the Pi and run the IoT Core client app

The Pi Python client has the following functionality:

  • Sign a JWT token with the device private key
  • Create and connect an IoT Core client
  • Create a Sense HAT sensor board client
  • Open the serial connection to the Arduino
  • Read the Sense HAT environmental sensors
  • Request the analog sensor readings from Arduino over the serial connection
  • Publish the sensor readings as a JSON document once a second
  • Re-generate and sign a new JWT token after it expires
  1. SSH to the Raspberry Pi with:

    ssh pi@YOUR_PI_IP
  2. Connect the Arduino to the Pi with a USB cable. This will power on the Arduino, and create a USB serial port on the Pi, for serial communications.

  3. On the Pi, check that you now have a serial port connected to the Pi. Execute:

    file /dev/ttyACM0

    The output should be similar to:

    /dev/ttyACM0: character special (166/0)
  4. With your virtualenv active, run the client app on the Pi, by executing:

    python ardu-pi-serial.py  \
        --project_id your_project_id \
        --registry_id my-registry \
        --device_id my-device \
        --private_key_file rsa_private.pem \
        --algorithm RS256 \
        --cloud_region us-central1 \
        --ca_certs roots.pem \
        --message_type event \
        --device_type pi

    To see the command line argument options, execute:

    python ardu-pi-serial.py --help

    If the client app starts correctly, you should see output similar to this:

    Creating JWT using RS256 from private key file rsa_private.pem
    Creating and flushing serial port. Rebooting Arduino..
    ('gcp_on_connect', '0: No error.')
    Received message '' on topic '/devices/my-device/config' with Qos 1
    Sleeping 3s..
    Received from Arduino: S s:89 w:42
    Publishing message: {"temperature": 37.32, "timestamp": "2018-07-25T08:29:59+08:00", "clientid": "raspberrypi", "humidity": 37.98, "pressure": 1016.98, "windgen": 0.21, "solargen": 0.43}
  5. On your local development machine, create a subscription for your IoT Core registry's telemetry topic, by executing:

    gcloud pubsub subscriptions create my-device-events-sub --topic=my-device-events
  6. Verify that your telemetry data is streaming to Pub/Sub, by executing:

    gcloud pubsub subscriptions pull my-device-events-sub --limit 100 --auto-ack

    You should see message payloads similar to:

    {"temperature": 36.62, "timestamp": "2018-07-25T08:42:10+08:00", "clientid": "raspberrypi", "humidity": 38.44, "pressure": 1017.05, "windgen": 0.1, "solargen": 1.2}   │ 151338809303544 │ deviceId=my-device

Now your Arduino and Pi are streaming telemetry data through IoT Core to Pub/Sub. You should see the sensor readings change if you expose the solar panel to more, or less light. The wind generator (DC motor) will start generating power, as you turn the rotor.


In part 2 of this tutorial, you will use Dataflow with a Python streaming pipeline to process this data stream, store it in Google BigQuery, explore the data with a Datalab Jupyter Notebook, and visualize it using Google Data Studio.

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