As with many young people interested in computing, I could never work out how a computer could turn 1's and 0's flowing through logic gates into what you see before you. You learn that this magic box can be programmed to do all sorts of amazing things, but are never really given the details as to how it does it. I wanted to know more, and after some research I started making logic gates with the one bit of electronics I knew how to use: Electric relays. I scrounged parts from cars, microwaves, scrap change machines, etc and put them together into increasingly complex contraptions. Two years later, I had TIM 8: a fully programmable 8 bit relay computer. This is the story of how TIM 8 came about, what I learnt along the way, and how relay computers are a fantastic way to demonstrate how a computer really works.
For the talk I would bring a presentation and TIM 8 (the size of a small suitcase).