In this project, taken from Charles Platt’s book Make: Electronics, we’re going to breadboard a fairly complex circuit using 555 timers and an OR logic gate.

Using these and some other, common components, we’ll build a game show button system. When one button is pressed, it automatically locks the other one out, until the quizmaster flips a reset switch.

“OR gates” are one of several types of basic logic gates. The logic of ORs are, as the name suggests, if input A or B is true (on), output X is true (on); thus, in this design, if either player presses his or her push button, the circuit will go true (on), locking out the other player’s button, and can only be reset via the toggle switch. This circuit is ideal for two-person quiz contests!

“I’ll take ‘Cool Projects’ for 100, Alex!”