robert.rozee Guru Joined: 31/12/2012 Location: New ZealandPosts: 2541
Posted: 04:29pm 24 Aug 2024
the 80-pin package only has 48 GPIO pins, including the 8 that have alternative functions as ADC inputs. plus you would want 3v3, ground, RESET, and for fun lets also include DP and DM (the two USB signals). also an onboard LDO regulator capable of handing up to 12 supply would be handy - rounding it out to an even 52 pins in total.
onboard it would make sense to have the SPI flash, a USB socket for uploading the firmware (this necessitates a regulator capable of taking the 5v USB supply down to 3v3). and why not also an HDMI socket and header to plug in one of those little microSD socket daughterboards?
if we subtract out the 8 GPIO pins for HDMI, and the 4 GPIO pins that we will use for the SD card interface (via a 6-pin header), that takes our 52 back down to... just 40 pins. this is no more than the existing pico PCB, a decidedly non-fragile number. and to accommodate the width of the HDMI socket, we can widen the PCB by an extra 0.2".