I think rather than pulleys, sprockets and photo-transistors, modern tinkerers would just feed the whole mess through a modern-day 35mm film digitizer (they're

I think rather than pulleys, sprockets and photo-transistors, modern tinkerers would just feed the whole mess through a modern-day 35mm film digitizer (they're quite common) and then just use a little software to work out what the squiggles represent. Edit: A post appeared suggesting this very thing as I typed. I hate when that happens.