Since all resistors are the same value we know that the voltage at the junction between the resistors are 2/3Vcc and 1/3Vcc (see image notes in fig 2). The purpose of these resistors is to set up a voltage divider between Vcc and ground. This consists of a few different elements: resistors, transistors, comparators, a flip flop, and an output stage.Īll three resistors diagrammed in fig 2 are 5kOhm (see image notes in fig 3). The second image is a close up of the diagram depicting the internal functional components of the chip. The positive supply voltage (+Vcc) should be between 5 and 15V. The power connections to the chip are through pins 1 (ground) and 8 (+Vcc). It's also a great starting point for audio projects because its output can be wired directly to a speaker.įig 1 shows the pin connections to the 555 timer, it was take directly from the 555 timer datasheet. The 555 timer is flexible, cheap, and easy to find (you can even pick them up at Radioshack). a steady clock/trigger to keep time in a circuit (astable mode) - the core oscillator of an analog synthesizer, with the addition of some op amps and other components this pulse wave can be shaped into a triangle, saw, and even sine shapes - a very basic chiptune style noise maker (see atari punk console) - time delay for an incoming signal (monostable mode) - very basic storage of input data/management of two button control system (bistable mode) Some applications that come to mind include: Jump straight to an example circuit for bistable mode here.

Jump straight to an example circuit for astable mode here.īistable Mode causes the 555 timer to toggle its output between high and low states depending on the state of two inputs.

In this mode the output of the 555 timer is switching between high and low states at a tunable frequency and pulse width. Jump straight to an example circuit for monostable mode here.Īstable Mode outputs an oscillating pulse signal/waveform. In this mode an external trigger causes the 555 timer to output a pulse of an adjustable duration. Monostable Mode is great for creating time delays.

By wiring the 555 timer with resistors and capacitors in various ways, you can get it to operate in three different modes: The 555 timer is a chip that can be used to create pulses of various durations, to output a continuous pulse waveform of adjustable pulse width and frequency, and to toggle between high and low states in response to inputs. This tutorial provides sample circuits to set up a 555 timer in monostable, astable, and bistable modes as well as an in depth discussion of how the 555 timer works and how to choose components to use with it.

555 timer pspice model