Lifts

The third kit in the How Things Work series. You build three lifts and a dispatcher from transistors: each car decides where to go by itself — it keeps going one way while there is work there, picks up calls on the way down, opens its doors and rings a chime; the Cancel button clears what was pressed. The dispatcher goes round the floors, computes the price of every car and gives the call to the cheapest. A segment screen shows three shafts — you see every decision and why the lift went past. It is a teaching model of the control logic, not a real lift. 11,422 transistors.

The introduction and lessons 0–1 are free; the rest opens after purchase.