For my projects, I have used a few different micro-controllers such as ATmega328p, ATtiny85v, ESP-01, and ESP32. In order to flash (programs or boot loaders) the micro-controllers, you need programmers. There are commercial products you can buy, but there are cheaper way to do the same.

There are two ways I usually use to flash the chips: 1) UART (using serial ports of the chip through serial to USB converter, FTDI for example); and 2) Arduino ISP (In-System-Programmer, using SPI (Serial Peripheral Interface) protocol).

I have made a programmer for the ATtiny85/ATtiny45 chips (see this post), and another one for ESP-01 (see this post). But for the other chips like ATmega328p DIP package, I usually program them with another Arduino board (Jeonlab mini v1.3 for example) and an FTDI break-out on a breadboard. For the ATmega328p TQFP package, I have used the Arduino as ISP method through SPI bus.

The ESP chips have pre-loaded firmware with a boot-loader, so I only need the FTDI breakout board with the RTS pin enabled.

Recently, I started thinking to integrate all these into a single board that consists of:

• FT232RL chip for FTDI
• ATmega328p TQFP with Arduino as ISP program loaded
• 5V to 3.3V regulator (600mA max.) for 3.3V output (FTDI has 3.3V output but 50mA max.)
• FTDI IO voltage selector (5V or 3V3)
• V-out selector (5V or 3V3)
• Programmer selector (ISP or FTDI)
• DIP socket for ATmega328p and ATtiny85/45
• ESP-01 programming socket header
• ISP output socket header
• FTDI output socket header
• USB type-C connector to PC

See more detail in my blog.

https://jeonlab.wordpress.com/2023/03/28/integrated-isp-ftdi-programmer-for-avr-and-esp/