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--- inhabitat:kaunas:day02 [2026/05/26 14:04] – created harley.lara
+++ inhabitat:kaunas:day02 [2026/05/29 09:05] (current) – jan.sonntag
@@ Line 1: / Line 1: @@
-====== Day 02 ======
+====== Day 2: Sensors and Communication ======
-===== WiFi Example =====
+Welcome to day two of our IoT workshop series! Today we will read a value
+from a soil moisture sensor, see it in the Serial Monitor, connect our board
+to WiFi, and finally send a message to an MQTT broker.
+We are using the **Arduino framework inside PlatformIO** throughout this workshop.
+===== 1. How a Capacitive Soil Moisture Sensor Works =====
+A capacitive soil moisture sensor measures how much water is in the soil by
+detecting changes in **capacitance** around its probe. Water and dry soil
+store electrical charge differently, so as the soil gets wetter, the
+capacitance the sensor measures changes. The sensor turns this into an
+**analog voltage**: drier soil and wetter soil produce different voltage
+levels, which our ESP32 can read.
+Unlike older resistive sensors, the capacitive type has **no exposed metal
+electrodes** touching the soil. This means it does not corrode nearly as
+quickly, making it much better suited for long-term use.
+We are using the **DFRobot Analog Capacitive Soil Moisture Sensor**.
+===== 2. Connecting the Sensor to the DOIT ESP32 =====
+The sensor has three wires:
+^ Sensor Pin ^ Connects to ESP32 ^ Purpose ^
+| VCC (red)    | VIN (5V) or 3V3 | Power |
+| GND (black)  | GND      | Ground |
+| AOUT (blue)  | An analog-capable GPIO (e.g. GPIO34) | Analog signal out |
+A few notes:
+  * The signal wire goes to an **analog input pin**. On the DOIT ESP32 DevKit, pins like **GPIO34, GPIO35, GPIO32, GPIO33** work well for analog reading.
+  * The sensor can run on either **3V3** or **5V**. The **VIN** pin on the DOIT ESP32 provides 5V (when the board is powered over USB).
+  * **Important:** the ESP32's analog pins can only safely read up to ~3.3V. If you power the sensor from 5V, its output range is higher, so be aware the readings will scale differently — and never feed more than 3.3V into a GPIO pin.
+  * Double-check GND is shared between the sensor and the board.
+<WRAP center round tip 60%>
+Here an example to connect to similiar MCU. Make sure to check the Pinout of your specific board!
+</WRAP>
+<imgcaption image3|Wiring of the analog sensor>{{ https://raw.githubusercontent.com/EOLab-HSRW/intro-to-iot/master/diagrams/wemos-soil_bb.png?400 |}}</imgcaption>
+<imgcaption image4|Schematic>{{ https://raw.githubusercontent.com/EOLab-HSRW/intro-to-iot/master/diagrams/wemos-soil_schematic.png?400 |}}</imgcaption>
+===== 3. Reading the Sensor with the Serial Monitor =====
+Before we send data anywhere, we want to **see** it. The easiest way is the
+**Serial Monitor**.
+**Serial** is a way for the ESP32 to send text back to your computer over the
+USB cable. By calling ''Serial.begin()'' once at startup and then
+''Serial.println()'' whenever we have something to show, we can print our
+sensor readings to the screen in real time. This is incredibly useful for
+checking that everything is wired correctly and that the numbers change when
+you touch the sensor or place it in soil.
+Open the Serial Monitor in PlatformIO and make sure the **baud rate matches**
+the value you set in ''Serial.begin()'' (commonly 115200).
+<code cpp>
+// PLACEHOLDER — Sensor reading code
+// This should:
+//   - start Serial at the chosen baud rate in setup()
+//   - read the analog value from the sensor pin
+//   - print the value to the Serial Monitor in loop()
+//   - add a short delay so the output is readable
+</code>
+Once uploaded, you should see numbers scrolling in the Serial Monitor.
+Try touching the sensor or dipping it into soil/water — the value should change.
+===== 4. Connecting to WiFi =====
+Now that the board works on its own, let's get it online. The ESP32 has
+built-in WiFi, so we just need to give it the **network name (SSID)** and
+**password** of our workshop access point.
+In ''setup()'' we tell the ESP32 to connect, then wait in a short loop until
+the connection succeeds. We can print the status to Serial so we know when
+we're online.
+<code cpp>
+// PLACEHOLDER — WiFi connection code
+// This should:
+//   - include the WiFi library
+//   - store the SSID and password
+//   - start the connection in setup()
+//   - wait until connected, printing progress to Serial
+//   - print the assigned IP address once connected
+</code>
+When it works, the Serial Monitor will show that the ESP32 has joined the
+network and received an IP address.
+===== 5. Introducing MQTT =====
+**MQTT** is a lightweight messaging protocol that is very popular in IoT. The
+idea is simple: devices send ("**publish**") messages to a central server (the
+"**broker**"), and other devices can listen ("**subscribe**") for them. Today
+we will only **publish** — sending messages out. We will not subscribe.
+{{pdfjs 500px>:latinet:unicaes:workshops:mqtt.pdf?75}}
+===== 6. Publishing a Message to the Broker =====
+For our final step, we connect to the **MQTT broker** and send a single
+message of **your choosing** — any text string you like, for example
+''"hello from my esp32"''.
+  * This is **not** the soil moisture value. That's a separate exercise. Here we are just proving we can talk to the broker by sending a simple string.
+  * We connect to the broker, then publish our chosen string to a **topic**.
+<code cpp>
+// PLACEHOLDER — MQTT publish code
+// This should:
+//   - include the MQTT client library
+//   - set the broker address and port
+//   - connect to the broker in setup() (after WiFi is connected)
+//   - publish a single text string of your choosing to a topic
+//   - print confirmation to Serial
+</code>
+Pick any message you want and send it. 🎉
+===== Recap =====
+By the end of today you have:
+  * Learned how a capacitive soil moisture sensor works
+  * Wired it to the DOIT ESP32
+  * Read its value in the Serial Monitor
+  * Connected the ESP32 to WiFi
+  * Learned the basics of MQTT
+  * Published your own message to the MQTT broker