In the previous episode, we learned about how 555 timers work on the inside. In this episode, we learn how 555 timers are used in circuits. There are three basic types of 555 timer circuits; astable, monostable, and bistable. Bistable circuits have two inputs that can manually set and reset the output of the 555 timer. Monostable circuits have one manual input and contain an RC circuit made of a capacitor and resistors. The manual input triggers the 555 timer output to be set high, and the RC circuit determines how long it will remain high until it causes the 555 to reset and the output to go low. Astable circuits are often the most commonly used of the three types. They have no stable output and no manual input, but rather the output automatically switches between high and low at a rate determined by the values of the RC circuit.