The Arduino Uno and Pro mini 5V both have exactly the same specs (https://www.arduino.cc/en/Products/Compare). However, why is it that they have different maximum program storage space? The UNO has a maximum of 32256 bytes whereas the Pro Mini 5V has a maximum of 30720 bytes.
The Uno uses a very nice bootloader named Optiboot that only requires a 0.5 kB boot section. The Pro Mini has an outdated, bloated, buggy bootloader that requires a 2 kB boot section.
You can free up 1.5 kB of program memory on your Pro Mini (assuming it's the ATmega328P instead of ATmega168 model) by doing this:
- Connect an ISP programmer to your Pro Mini
- Tools > Programmer > select the appropriate programmer
- Tools > Board > Arduino/Genuino Uno
- Tools > Burn Bootloader
After doing that you must use the Pro Mini as an Uno from then on. This has the added advantage of allowing you to use the watchdog timer without going into an endless reset loop, which is the bug in the standard Pro Mini bootloader.
Thanks, how do I connected the ISP programmer to the Pro Mini. Can the ISP programmer be an UNO?
Yes, load the ISP sketch in examples
it indicates to use these pins
