Just purchased some ATmega32u2's for a project and don't know what external hardware I need to program them to interact with USB. I googled a bit and found some schematics, such as the ones here or here, but they all seem to be missing information and/or conflicting. It seems I need an 8Mhz crystal resonator for USB timing, but I don't want to mix parts of multiple schematics in case of some issue. Do I even need external hardware other than a USB port? My intent is to use it with the HID-project library.
Top hit on google search for "atmega32u2 usb example", with other very relevant posts following:
https://helentronica.com/2015/07/23/getting-started-with-atmega8u2-and-other-avr-usb-microcontrollers/
Why not use Atmega 32U4, the same processor as comes on Arduino Leonardo and Pro Micro. You can buy a clone "Pro Micro" development board on eBay shipped from China for about $2.50USD each. Processor runs at 5V, 16MHz. This clone board already has micro USB connector installed.
Why?
The problem with the 32u2 is that - as far as I know - there is no core to add support to them to the Arduino IDE, so it's Atmel Studio, or some other IDE. IIRC the xu2 series also doesn't have an ADC.
Whereas there is a core for the 32u4 which is extremely well exercised and supported, since it's used for micro/leo/etc.
The ATmega32u2 has only two timers, UART and SPI hardware. It lacks the ADC and I2C.
Eeew, no I2C? Not even via a USI?