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Weather Station

At a glance

What you'll build: a small weather station that measures the temperature and humidity of the room, shows the readings on an LCD display, and flashes an LED when the temperature gets too high.

Smart-city pillar: 🌿 Smart Environment & Climate Monitoring — in a real city, hundreds of these sensors feed data into air-quality monitoring and climate-adaptation systems.

Prerequisites: DHT11 lesson, LCD lesson, White LED lesson.

Time: about 45 minutes.

Overview

Modern cities operate networks of environmental sensors — on streetlight poles, on buildings, in parks. The data they collect shapes decisions about traffic (ozone alerts), public health (heatwave warnings), and infrastructure design (which neighbourhoods need more shade trees).

In this project you'll build a single node of that network. Your weather station:

  1. Reads air temperature and humidity from a DHT11 sensor
  2. Shows the current readings on a 1602 LCD display
  3. Lights an LED as a high-temperature warning when it exceeds 28 °C

Once this is working, Part 4 will show you how to send those same readings to Flowlence Cloud so an entire classroom's worth of weather stations can be compared on one dashboard.

Components needed

Everything on this list is in your Flowlence IoT Kit — no breadboard or extra wires needed.

Component Quantity From your kit
ESP32 Plus board 1 ✅
DHT11 Temperature & Humidity Sensor 1 ✅
1602 LCD Display (I²C) 1 ✅
White LED module 1 ✅
3-pin Dupont cables 3 ✅
USB-C cable 1 ✅

How it works

┌─────────────────────┐        ┌──────────────────────┐
│  DHT11 reads         │───────►│ ESP32 brain          │
│  temp & humidity     │        │  - decide what to do │
│  every 2 seconds     │        │  - format display    │
└─────────────────────┘        └─┬─────────────┬──────┘
                                  │             │
                          ┌───────▼─┐      ┌────▼──────┐
                          │ 1602 LCD │      │ LED       │
                          │ shows:   │      │ ON if     │
                          │ Temp: X  │      │ temp > 28 │
                          │ Hum:  Y  │      │ OFF else  │
                          └──────────┘      └───────────┘

Wiring

Three 3-pin Dupont cables, three sensor modules, three plug-in connections. That's it.

Weather Station — DHT11, LCD, and LED plugged into the ESP32 Plus shield

Sensor ESP32 Plus pin
DHT11 Temperature & Humidity IO 15
1602 LCD Display (I²C) SDA / SCL header (top of board)
White LED module IO 5

Step by step:

  1. Unplug the USB cable from your ESP32 Plus.
  2. Plug a 3-pin cable between the DHT11 module and pin IO 15 (match S / V / G at both ends).
  3. Plug a 4-pin I²C cable between the LCD module and the dedicated I²C header on the ESP32 Plus (labelled GND V SDA SCL near the top of the board).
  4. Plug a 3-pin cable between the White LED module and pin IO 5.
  5. Plug the USB cable back in.

Disconnect USB before wiring

You know the drill by now — unplug, wire, plug back in.

Step-by-step code

Rather than writing the whole program in one go, build it in three stages and test after each. This is how real engineers work — it isolates bugs quickly.

Stage 1 · Read and print the DHT11

This is exactly the program from the DHT11 lesson. We start here to confirm the sensor is wired correctly before adding the LCD and LED.

Stage 1 blocks — DHT11 only, print to serial

Test it: upload, open Serial Monitor, confirm you see temperature and humidity numbers that move when you breathe on the sensor.

Stuck? Don't move on.

If the Serial Monitor shows nan or 0.00, your DHT11 isn't talking. Recheck wiring against the table above before adding more components.

Stage 2 · Show the readings on the LCD

Now replace the serial print blocks with LCD blocks. Your program is still just reading and displaying — no logic yet.

Stage 2 blocks — same readings, now sent to LCD

What's new:

Block What it does
init lcd I2C address 0x27 Tells Flowlence to use the 1602 LCD at its default I²C address
lcd set cursor column 0 row 0 Moves the "write head" to the top-left of the display
lcd print "Temp: " Prints text
lcd print (read dht_1 temperature) Prints the temperature value after the "Temp: " label

Test it: upload, watch the LCD. It should update every 2 seconds.

LCD shows garbled characters or nothing at all?

The I²C address might not be 0x27. Try 0x3F instead — those are the two common defaults. If neither works, see Troubleshooting.

Stage 3 · Add the temperature alert

Now we add decision logic — the ESP32 has to think about the reading and do something different based on it.

Stage 3 blocks — full program with if/else for LED

What's new:

Block What it does
if (temp > 28) then … else … Checks the condition every time through the loop
set pin 5 to HIGH Turns White LED on when hot
set pin 5 to LOW Turns White LED off otherwise

Testing

Once you upload Stage 3, run through this checklist:

  • [ ] LCD line 1 shows temperature updating every 2 seconds
  • [ ] LCD line 2 shows humidity updating every 2 seconds
  • [ ] Breathing on the DHT11 makes the humidity number jump up
  • [ ] Warming the DHT11 (cup your hand around it) eventually makes the LED turn on
  • [ ] When the sensor cools down, the LED turns off

If all five boxes check, you've built a working smart-city environment node. 🎉

Extend it

Pick one of these and make it yours — this kind of creativity is exactly what the BGC judges look for.

Extension 1 · Multi-threshold warning

Add a buzzer. Design a three-tier alert:

  • < 25 °C: LED off, buzzer silent
  • 25–30 °C: LED on steady

  • 30 °C: LED flashing + buzzer beeping

Extension 2 · Humidity tracking

Warn when humidity drops below 30 % (too dry — uncomfortable for people) or rises above 70 % (too humid — risk of mould). Use the LCD second line to display the warning text.

Extension 3 · Historical max/min

Create two variables, max_temp and min_temp, that remember the highest and lowest temperatures seen since the program started. Show them on an extra screen that appears every 10 seconds.

Extension 4 · Cloud dashboard (Advanced)

When Part 4 is ready, connect this weather station to Flowlence Cloud. Your teacher can then see every student's weather station on one classroom dashboard. This is the real smart-city workflow.

What's next?