Retired Electronics Engineer; Learnt my Trade when : NPN and PNP had significant meaning, a soldering Iron was often needed complicated systems had lots and lots of PCBs fault finding often required an oscilloscope rather than a laptop. Over the 40 years saw huge changes in hardware and software which only helps a little in sussing out R Pi hardware and software. Now playing with 1 R Pi 3 (shit! this thing is like using an real PC) 2 R Pi Zero (favorite thing for the little projects that I am getting in to) 1 ancient R Pi 1 poor little thing must be psychologically scared by years of neglect in a dark drawer 1 newer R Pi 2 (now that`s better, now enough USB sockets) ©