The 555 Timer

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The 555 Timer
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What is a 555 timer?

• The 555 timer is one of the most remarkable
  integrated circuits ever developed. It comes in a
  single or dual package and even low power CMOS
  versions exist
• The 555 timer consists of two voltage
  comparators, a bi-stable flip flop, a discharge
  transistor, and a resistor divider network.

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Applications for 555 timer

• The 555 timer can be used in many ways and is
  very versatile.
• Common uses are for precision timing, pulse
  generation, sequential timing, time delay
  generation and pulse width modulation (PWM).
  (ie.motor speed control)

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Pin Configuration
Pin1 ground Pin2 trigger input to
lower comparator Pin3 output high ( 200mA
max) Pin4 reset latch to low state
5
Pin Configuration
Pin5gives access to voltage divider
Pin6 input to upper comparator Pin7 an
open collector to discharge Pin8 power
source
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Two operations

• Astable
• Acts as a timer
• Pulses at precise intervals.
• Most popular

• Monostable(one-shot)
• Outputs only a single pulse

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555 timer Wiring

• 1st step is to connect pins 2 and 6 together.Then
  give power to pins 4,and 8 and ground pin 1.

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2nd part

• 3 components are needed to make 555 timer work.
• 2 resistors(R1,R2), and a capacitor(C1).
• These components determine how fast the timer
  will work in hertz.
• The equation to figure out what hertz they will
  run at is
• 1.44 / ((R1 (2 R2) C)

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Resistors

• R1 goes between pins 8 and 7, so we'll put a
  1,000 ohm resistor there. R2 goes between pins 7
  and 6, so we'll put a 5,000 ohm resistor there.

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Capacitor

• Now it's time to add the capacitor. It goes
  between pins 6(threshold) and pin 1 (ground). Now
  this circuit is ready to be used!

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Output to LED

• The output of the timer is pin3 so now its time
  to connect an LED with a wire, then connect a
  resistor from the negative end of the LED to
  ground for protection.

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What is my frequency??

• If I used a 1,000ohm resistor for R1, and a 5,000
  ohm resistor for R2, and a 130 microfarad
  capacitor(0.00013 F), at what hertz is my LED
  going to be flashing?

1.44 / ((1000 2 5000) 0.00013) 1.44 /
((1000 10,000) 0.00013) 1.44 / (11,000
0.00013) 1.44 / 1.43 1 (Approximately)
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Overview

• 555 timer is very versatile.
• Consists of two voltage comparators, a bi-stable
  flip flop, a discharge transistor, and a resistor
  divider network.
• Can be wired as Astable or monostable
  multivibrators.
• Astable most popular (timing)