I have been looking at providing a single 7 segment LED display for some little projects using a Nano. but I didnt want to have to make any sub-board to mount it on
I found on EBay you can buy 0.5" 7 seg displays that fit absolutely perfectly across the pitch-width of a Nano, they cost about 10p each from China.
It would use pins PC0 to PC4 at the top and PB1/PB0/PD5-PD7 at the bottom (or the other way up if you wish)
The display is perfectly positioned so that you can still access the reset button, it doesn’t interfere with the other LEDs, does not use any of the SPI connections, or the RX/TX lines, although it does interfere with the I2C SDA line
I am thinking of driving this with a very low ratio manually generated PWM, without resistors.
Its a sackable offence in engineering terms… but it WILL work if the segments are all driven separately rather than all together.
I have done a quick mock-up in the attached drawing…