The ESP32 is the latest and greatest wonderchip from Espressif. It’s a 32-bit, dual-core chip with WiFi, Bluetooth, and tons of peripherals such as CAN and Ethernet. For most of these peripherals, Espressif already has a few bits of example code, but [Frank Sautter] didn’t like the Ethernet implementation. The ‘stock’ code calls for a TLK110 Ethernet PHY, but that’s an expensive chip when bought in quantity one. A better chip would be the LAN8720, so [Frank] built a board to enable Ethernet on the ESP32 with this chip.
The ESP32 only needs a few components to wire it into an Ethernet network. Just a few resistors, capacitors, and an RJ45 jack will take care of most of the work, but because he’s taking the Ethernet ‘shield’ route, he needs to add his own Ethernet PHY. The Waveshare LAN8720 is the chip for this, but there’s an issue with the pin configuration of the ESP32. GPIO0 on the ESP32 has two functions — the first is pulling it low during startup for serial programming, and the second is the clock input for the EMAC function block. Some bit of circuitry must be devised to allow for both conditions to enable Ethernet on the ESP32.
[Frank]’s solution is to add a few pull-up and pull-down resistors to a breakout board, and use an unused GPIO pin to switch GPIO0 high during startup, but allows a crystal to grab it a bit later. It’s a hack, certainly, but it does allow for some much cheaper chips to be used to give the ESP32 Ethernet.