# Know Your IC: 555 Timers

## Step 2: Function of the Chip

The 555 integrated circuit is commonly called the "555 timer" but that is only one of it's uses. The chip can be used both as a timer and as an oscillator.

WHAT DOES THAT MEAN?
Well i'm glad you asked. An Oscillator is something that produces and constant electrical wave, like a sine or square wave. The timer will pulse at a specific interval depending on the components attached.

The 555 chip has 3 main modes:
• Monostable Mode for "One Shot" pulse generation:
• Astable Mode for putting out a continuous stream of pulses. (aka timer):
• Bistable mode for acting like a Schmitt trigger.

The Pin out of the 555 timer is as follows:
Pin 1: Ground
Pin 2: Triggering the timer, connecting this to ground starts the chip up.
Pin 3: Output, stays at whatever Vcc is
Pin 4: Forces pin 3 to low if grounded
Pin 5: Used to adjust trigger threshold.
Pin 6: Threshold that ends timer when 2/3 of Vcc is reached.
Pin 7: Discharge, connects to ground when output is low
Pin 8: Power, denoted in most contexts as Vcc

Images above are borrowed from: http://clarkson-uk.com/555-timer/
Resources: http://www.markallen.com/teaching/ucsd/147a/lectures/lecture4/5.php
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makincoolstuff says: 2 years ago
howed you get the animations on?
Snappy83 says: 2 years ago
Thanks for the tutorial man! much appreciated! allways wondered what they ment by mono and astable. cheers!
115494 says: 2 years ago
Hey I was wondering if you could show me how to make a monostable mode without the lights. Thanks.
YOGESH YADAV says: 3 years ago
what are the adjustable timer circuit of 555.....???
Abume4life says: 3 years ago
i have lm741 cant arrange the other component cause i dont have the circuit diagram
heeeeeeeeeeeeeeeeeelp
8v92 says: 3 years ago
Good project! If you need equal on/off times a 74xx or 40xx counter can be used with the LM555 as long as Vcc is at 5 volts.