There’s only one GPIO pin broken out, and it’s pre-wired to an LED. That’s the bad news, and depending on what you want an ESP32 for, it might not phase you at all. What is impressive here, if not the number of I/O pins, is the size of the board: at 9.85 mm x 8.45 mm barely overhangs the USB-C socket that takes up one side of the board.

In order to get the ESP32-C3FH4 onto such a tiny board, all of the other support hardware had to be the smallest possible sizes– including resistors in 01005. If you don’t speak SMD, one could read that number code as “oh god too small” — at 0.4 mm x 0.2 mm it’s as minuscule as you’ll find– and [Pegor] hand soldered them.

OK, he did use a hot plate for the final step, but he did tin the pads manually with a soldering iron, which is still impressive. Most of us probably would have taken PCBWay up on their offer of assembly services, but not [Pegor]. Apparently part of the reason for this project was that he was looking for an excuse to use the really small footprint components.

Aside from leaving out GPIO and needing too-small SMD components, [Pegor] admits that pesky little details like antenna matching circuits and decoupling capacitors had to get cut to make the tiny footprint, so this board might be more of a stunt than anything practical. So what can you do with the smallest ESP32 board? Well, [Pegor] put up a basic web interface up to get you started blinking the built-in LED; after that, it’s up to you. Perhaps you might fancy a teeny-tiny minecraft server? If you can stand to increase the volume a little bit, we’ve seen how to hack a C3 for much better wifi performance.

f32 - an extremely small ESP32 board

The f32 is an ultra-compact ESP32 development board designed to mount directly behind a USB-C receptacle. The PCB measures just 9.85 mm x 8.45 mm. It's powered by the ESP32-C3FH4 microcontroller and was created primarily for research and as a bit of a stress test for the ESP32, since it intentionally ignores many standard design guidelines. There's only one exposed GPIO and it is connected to an onboard LED, so most of the development on here would be more catered for wifi/web. To test the f32 an example application was created that users can interact with. The application turns the f32 into a captive portal so when it's powered on it will show up as an open access point that the user can select from available WiFi networks. The user is then automatically sent to the f32's control page where they can interact with some of its basic functionality such as turning on an LED or scanning for surrounding WiFi networks. There's also an "About" page that provides a small overview of the device.

The PCB was designed using DipTrace and manufactured by PCBWay with a board thickness of 0.6mm, min hole size of 0.2mm, and min track/spacing of 4/4mil. At the time of making this it only cost $10.75 for 5 boards shipped! That still blows my mind. PCBWay does also offer assembly services, but I chose to assemble this at home and suffer a bit. This took a bit of trial and error with such small parts, but I decided the best way for me was to ditch the stencil and make flux my best friend.