Build Your First IoT Project with Raspberry Pi, DHT11, and ThingSpeak

Internet of Things (IoT) is reshaping how we interact with everyday devices. With sensors that stream data to the cloud, you can monitor and manage environments from anywhere. If you're new to IoT, a simple temperature, humidity, and light monitor is an excellent starting point.

In the humid Northeast summer, basement conditions can vary dramatically. My workshop sits in a basement with a dehumidifier that keeps the air dry, yet it remains cooler than the summer temperatures outside. I wanted to know exactly how cool and humid it gets, which inspired this first IoT project.

DHT11 sensors are affordable and read temperature and relative humidity. While they aren't laboratory‑grade accurate, they are sufficient for monitoring a basement environment. I also added a cheap photoresistor to detect whether lights were left on.

Instead of building a custom web server, I chose ThingSpeak, a cloud service with a simple API for posting and visualizing sensor data.

Step 1: What you need to complete this project

We’ll prototype on a breadboard, so no soldering is required. Once the design is verified, you can transfer it to a PCB if desired.

Hardware:

• Raspberry Pi 2 with SD card and Raspbian OS
• USB power supply
• USB cable
• Breadboard and jumper wires
• 2 × DHT11 sensors
• 2 × 10 kΩ resistors
• 2 × photocells (photoresistors)
• 2 × 1 µF capacitors

Step 2: Prepare the Raspberry Pi

First, install Raspbian on your Pi. If you need help, refer to the Soldering Sunday guide or the official Raspberry Pi OS installation guide.

Next, enable Python support for GPIO access. You’ll need the Adafruit GPIO and DHT libraries. Follow the official Adafruit tutorials:

• GPIO Setup
• DHT11 Sensor Library

Step 3: Understanding GPIO Pins

GPIO (General Purpose Input/Output) pins are the bridge between your Pi’s software and external hardware. All Raspberry Pi models share pins 1–26; newer boards add pins 27–40. Always double‑check the physical pin number against the GPIO numbering used in your code to avoid miswiring.

For a deeper dive, consult the GPIO tutorial.

Step 4: Build the Circuit

Power off the Pi before connecting the breadboard to prevent damage. Use Dupont jumper cables (female to Pi header, male to breadboard).

Connect the following:

• DHT11 – Pin 1 to 3.3 V, Pin 2 to Pi GPIO 23 (pin 16) with a 4.7 kΩ pull‑up resistor to 3.3 V, Pin 4 to Ground.
• Photoresistor – One leg to 3.3 V, the other to Pi GPIO 24 (pin 18). Place a 1 µF capacitor between the photoresistor leg and Ground to filter noise.

Verify your wiring against the attached Fritzing diagram and photos.

Step 5: Set Up ThingSpeak for IoT Data

Visit ThingSpeak, create a free account, and add a new channel. Name the channel and its fields (e.g., Temperature, Humidity, Light). Note the order of the fields; this determines how you’ll post data later.

Choose channel visibility (public/private) and provide a location if desired. Copy the channel’s Write API key; it will be required in your Python script to publish data.

With the hardware wired and the channel configured, you’re ready to write a Python script that reads sensor values and posts them to ThingSpeak. Once the script is running, your basement environment will be visible from anywhere.