PROJECT 11 · CLOUD / MQTT

MQTT + Ubidots: Cloud Dashboard and Control

Send DHT11 readings to a live cloud dashboard, and switch an LED or relay back from anywhere.

⬇ Download the sketch Save Project_11_ESP32_MQTT_Ubidots.ino, then open it in the Arduino IDE. Needs the Ubidots ESP32 MQTT, DHT sensor library, and Adafruit Unified Sensor libraries, plus your Wi-Fi and Ubidots token.

1 · Why MQTT

In Projects 5 to 9 the ESP32 was a web server: your phone had to be on the same Wi-Fi and had to keep asking for data. MQTT flips that around. Devices publish messages to a broker, and anyone interested subscribes. It is lightweight and works from anywhere with internet.

DHT11 --> ESP32 --publish--> [ Ubidots broker ] --> Dashboard (you watch) LED <-- ESP32 <--subscribe-- [ Ubidots broker ] <-- Switch widget (you control)

Term	Meaning	Here
Broker	Server that routes all messages	Hosted by Ubidots
Publish	Send a value to a topic	ESP32 sends temperature, humidity
Subscribe	Ask to receive a topic	ESP32 listens for `led`

2 · Get your Ubidots token

Sign up for a free Ubidots STEM account at stem.ubidots.com.
Open your profile, then API Credentials, and copy the Default token (looks like BBUS-xxxx).
No need to create the device by hand: it appears the first time the board publishes.

3 · Libraries and wiring

Install from the Library Manager: Ubidots ESP32 MQTT (pulls in PubSubClient), DHT sensor library, Adafruit Unified Sensor.

Qty	Part	Notes
1	ESP32 · breadboard · jumper wires	as always
1	DHT11 module	S to GPIO 4, + to 3.3 V, - to GND (same as Project 9)
1	LED + 220 Ohm, or the relay from Project 7	to GPIO 26 (the thing the cloud switches)

This is Project 9's sensor plus Project 7's actuator on one breadboard. Nothing new to wire, only new code.

4 · Edit, upload, watch

Edit the marked block at the top of the sketch: WIFI_SSID, WIFI_PASS, UBIDOTS_TOKEN, and a unique DEVICE_LABEL. Upload, then open Serial Monitor at 115200:

==============================================
 Project 11: ESP32 + MQTT + Ubidots
==============================================
DHT11 data -> GPIO 4
Output      -> GPIO 26
[PUB] temperature: 24.6 C, humidity: 41.0 %
[CLOUD] led -> ON (raw "1")

5 · Build the dashboard

In Devices, confirm your device appeared with temperature and humidity.
Add a control variable: open the device, Add Variable, type Raw, name it exactly led.
In Data, Dashboards, add a Gauge on temperature, a Line chart on temperature and humidity, and a Switch on led.
Flip the switch. The board's LED or relay follows within a few seconds.

6 · Troubleshooting

Symptom	Likely cause	Fix
Serial stops after Wi-Fi	Wrong token	Re-copy the Default token
No device in Ubidots	Never published	Check DHT reads numbers, not `--`
Switch does nothing	Variable not named `led`	Name it exactly `led`
Reconnect loop	5 GHz Wi-Fi	ESP32 is 2.4 GHz only