Catalogue

The ESP32's older, cheaper sibling: single core, Wi-Fi only, and still perfectly good for anything that just needs to get a reading onto a network. If your project is a sensor that posts to a server every minute, this does it for less. 3.3 V logic, not 5 V tolerant. Note the silkscreen labels (D1, D2...) do not match the GPIO numbers you use in code — D1 is GPIO5, D2 is GPIO4. Keep a pinout to hand.

An ESP32 with a camera module and a microSD slot, sold as one board. It runs a web server that streams video over Wi-Fi with about ten lines of setup, which makes it the cheapest way to put a camera on a network. The gotcha that catches everyone: there is no USB port on it. You need a separate USB-to-TTL adapter to program it, and you must jumper GPIO0 to GND to enter flash mode, then remove the jumper and reset to run. Order an adapter with it if you do not already have one.

Dual-core ESP32-WROOM-32 with Wi-Fi and Bluetooth on board. This is the part that replaces an Uno plus a wifi shield plus a bluetooth module, usually for less than any one of them, which is why most new connected projects here start on it. GPIO are 3.3 V and not 5 V tolerant — a 5 V sensor output needs a divider or a level shifter before it touches a pin. Boards come as 30-pin or 38-pin; ask if your enclosure or shield depends on which.

A small single-core S2 board with native USB, which is the interesting part: it can present itself to a computer as a keyboard, a mouse or a mass-storage device without any extra hardware. Good where board space is tight. Note the S2 has Wi-Fi but no Bluetooth — if you need BLE, take the plain ESP32 or an S3 instead. Also 3.3 V logic, not 5 V tolerant.