Lab 10 - Getting started with Arduino & ESP32

Introduction: Breadboards & Components

We will assemble a basic circuit for reading an analog sensors value and controlling a LED. Components we will work with are:

• ESP32 development board - A microcontroller board with integrated WiFi and Bluetooth capabilies.
• Light Emitting Diode (LED)
• Resistors
  • 10kΩ Resistor - let's label it R1
  • 100Ω Resistor - let's label it R2
• Photocell, also known as Photoresistor, a kind of resistor whose resistance is based on the light level.
• Breadboard and jumper wires - for laying out the components.

Setting up

• Install latest version of Arduino Desktop IDE
• Also install USB-UART drivers
• Start Arduino and open Preferences window.
  • File -> Preferences or Arduino -> Preferences (macOS)
• Enter https://dl.espressif.com/dl/package_esp32_index.json into Additional Board Manager URLs field. You can add multiple URLs, separating them with commas.
• Open Boards Manager from Tools > Board > Boards Manager menu and install esp32platform(esp32 by Espressif Systems)
  • After installing, you can select ESP32 Dev Module board from Tools > Board as the currently used board.
  • You also have to specify the (USB) port to use (assuming device has been connected!)
    • On Windows it will be something like: COM4
    • On Linux, it will be something like: /dev/tty/USB0
    • On Mac, it will be something like: /dev/cu.usbserial-0001

Hello World

The ESP32 board has a serial port connected to the micro USB port, through this we can communicate with the board: write programs to it and see output from running programs.

Let's write a simple program which prints something to the serial port.

• Create a new project. In setup() :

 Serial.begin(9600);    // initialize serial communication at 9600 bits per second
 Serial.println("Running setup() function!");

In loop():

 Serial.println("Hello!");
 delay(1000);          // wait for a second

• Compile & Upload the code to your board, then open Serial Monitor (Tools > Serial Monitor).

You should be able to see the output we printed in code:

• If you are seeing connecting....____.... for more than 10 seconds, then try holding the "BOOT" button on the board while Arduino uploader is connecting to the board.

Establishing power rails on the breadboard

Now we can start adding additional components to our set-up.

• Wire the common ground (GND) pin from ESP32 to the negative (blue) power rail of the breadboard
• Wire the 3.3V pin from ESP32 to the positive (red) power rail of the breadboard.

As a result, our components have easy access to both GND and voltage source, regardless of where they are physically placed on the breadboard.

Reading a Sensor - Photoresistor

We will add the photocell, wiring it up to form a voltage divider circuit. See here (scroll to Reading Resistive Sensors) for more information.

Wiring:

• From one leg of the photocell, there's a connection to R1 and pin D2 of ESP32
• The other leg of the photocell is connected to the 3.3V power line.
• The R1 is connected to photocell on one leg, and to GND.

Add the photoresistor, together with resistor R1 as shown below:

Code:

Outside of the setup() or loop() functions, let's put the pin we are using to read analog values in a constant:

    const int sensorPin = 2;
    int lightVal;   // light reading

• In loop():

   lightVal = analogRead(sensorPin); // read the current light levels
   //TODO: write value to serial output

Finish the above code and run the code. Then, you should be able to see numeric values in your Serial Monitor. Try also using the Serial Plotter.

Controlling a LED

Wiring:

• Connect the negative LED leg to GND.
• Connect the positive LED leg to R2
• Connect the other leg of R2 to D5 of ESP32.

Code:

const int ledPin= 5; - store reference to sensorPin we are using First, we have to setup the LED pin to act as an output:

    // inside setup():
    pinMode(ledPin, OUTPUT);

We can change the state of the LED with:

    //inside loop():
    digitalWrite (ledPin, HIGH); // turn on light
    delay(500);
    digitalWrite (ledPin, LOW);  // turn off light
    delay(500);

The above code, will blink the LED at 500ms interval.

Feedback loop

Now, write code which turns the LED on or OFF based on a fixed light sensor value. You can use a simple if-else based logic.

For reference on the Arduino language, you can refer to the documentation. For this task, it is useful to check Control structures -> Else.

[Optional Bonus task] Smoothing

The raw light values are quite sensitive and a bit noisy. A good idea in this situation would be to consider the average of multiple sensor measurements instead of just one. Try to put together code which periodically outputs the average sensor value instead of a single measurement. ( See: https://www.arduino.cc/en/Tutorial/BuiltInExamples/Smoothing )