If you search for how to read a temperature sensor, a soil probe or a motion detector with a microcontroller, the top results are almost all Arduino. That is not because Arduino boards are the most powerful or the cheapest. It is because nearly everything around them is easy to find, easy to copy and likely to work the first time.
A short history
Arduino began around 2005 at the Interaction Design Institute Ivrea in Italy, as a cheap board that design students with no electronics background could program. The design was released as open source, which let other companies make compatible boards and kept prices low. The Uno, released in 2010, became the board that most tutorials assume you own.
What people like about it
- It starts fast. Plug the board into a USB port, open the editor, paste a short example and press upload. A blinking light can take five minutes, including the download.
- The libraries exist. For almost any common sensor, such as a DHT22, a BME280 or a DS18B20, someone has already written a library, and the maker's own tutorial uses it. You call one function to get a temperature.
- The community answers questions. The Arduino forum and the wider internet hold years of solved problems. A strange error message is nearly always something another person has already hit.
- The hardware is forgiving. Classic boards run at 5 volts and tolerate a lot of rough handling. Pins are clearly labelled, and a mistake rarely destroys anything.
- The code is plain. Sketches are written in C++ with a thin layer on top. The structure is two functions, one that runs once at start and one that repeats. That is easy to hold in your head.
- It does one job predictably. There is no operating system. A sketch that reads a sensor every second reads it every second.
Where the classic boards run out
The Uno uses an ATmega328P chip, with 32 KB of program memory, 2 KB of working memory and a 16 MHz clock. That is plenty for reading sensors and driving a display. It runs out quickly when you add networking, text handling or anything that needs a big buffer.
- No network. A classic Uno has no Wi-Fi. You need an add-on module, or a different board.
- Modest analog input. The built-in converter reads 10 bits, which is 1024 steps. Fine for a soil probe, coarse for precise measurement.
- Tight memory. Building a long web address as text can use a visible share of the 2 KB.
- Encryption is hard. Secure web connections need more memory and speed than the smallest boards have.
What to move to when you need the internet
The popular answer is the ESP32 and its older sibling the ESP8266. These are inexpensive chips with Wi-Fi built in, and they can be programmed from the same Arduino editor and with the same libraries. You keep everything you learned and gain a network connection. The ESP32 also has Bluetooth, more memory and a faster clock. Arduino's own newer boards, such as the Uno R4 WiFi and the Nano ESP32, give you the same with the official logo.
If your project needs to run a full program or a database, a Raspberry Pi is a better fit than any microcontroller. It is a small computer, not a chip.
The part nobody mentions in the tutorial
Most Arduino tutorials end when the number appears in the serial monitor. The temperature prints to a window on your laptop and the project is declared finished. But a reading that only exists on a laptop screen is not much use. You want it on your phone, you want yesterday's values, and you want a message when something goes wrong.
That gap is where a dashboard comes in. The usual path is to have the board send each reading over Wi-Fi to a service that stores it and draws charts. The simplest way to do that is a plain web request, which any ESP32 sketch can make in a dozen lines. We walk through it in sending ESP32 sensor data to a website, and the Arduino page has the short version.
Picking a board for a sensor project
| You want to | Use |
|---|---|
| Learn, or read a sensor and show it locally | Arduino Uno or Nano |
| Send readings over Wi-Fi from a small battery device | ESP32 or ESP8266 |
| Reach beyond Wi-Fi range with tiny messages | A board with a LoRa radio |
| Run several programs, a camera or a database | Raspberry Pi |
For most home sensor projects the ESP32 is the sensible default. It costs little, uses the tools you already know, and puts your readings on the internet without any extra parts.