555 Timer Pin configuration n The 555 timer

555 Timer

Pin configuration n The 555 timer consists of; Two voltage comparators n A bi-stable flip flop n A discharge transistor n and a resistor divider network. n

Internal Circuit Of 555 Timer

VCC 8 Control Voltage 5 4 Reset 5 K VA Threshold 6 + C 1+ RD Q 5 K Trigger 2 VB + C 2 + SD Q 5 K Discharge 7 T Discharge Transistor GND 1 RS-FF Voltage Divider Comparator 3 Output

The result for comparing VCC 2/3 VCC 5 K . V 5 A 6 + C 1 + 5 K 2 VB 5 K 1/3 VCC . + C 2 + RD V 6 V 2 R D SD <2/3 VCC <1/3 VCC 1 0 >2/3 VCC >1/3 VCC 0 1 SD <2/3 VCC >1/3 VCC 1 1 >2/3 VCC <1/3 VCC 0 0 Not permitted

RD Q SD Q RD 1 outp 0 ut 1 T V 6 V 2 SD 0 Q 1 T off 1 0 on 1 remain Q T <2/3 UCC <1/3 UCC 1 off >2/3 UCC >1/3 UCC 0 on remain 保持 remain <2/3 UCC >1/3 UCC 保持

Monostable Multivibrator & Waveforms

Monostable Multivibrator (One-shot) Operation +VCC R 1 5 6 1 ui 2 5 K VA + C 1+ VB + C 2+ T on 01 5 K 7 5 K u. C >2/3 VCC 4 (Re) VCC 8 1 (grand) 1 Steady state 1 RD Q SD Q 0 3 u. O Q=0

Monostable Multivibrator (One-shot) Operation +VCC R 1 5 6 ui 0 4 (reset) VCC 8 2 5 K VA + C 1+ 5 K VB + C 2+ 7 5 K u. C T < 1/3 UCC off 1 (grand) Transiet state 10 1 01 RD Q SD Q 01 3 u. O Q=1

Monostable Multivibrator(One-shot) Operation +VCC R 1 5 6 1 ui uc >2/3 VCC 4 (reset) VCC 8 2 5 K VA + C 1+ 01 5 K VB + C 2+ 7 5 K 01 RD Q SD Q 01 Steady state 10 3 u. O Q=1 Q=0 T 1 (grand)

What is a monostable multivibrator? • With one stable state • Normally in its stable state, to change to its unstable state only when triggered • Once triggered, to remain in its unstable state for a predetermined length of time and then return to its stable state automatically ui t u. C 2/3 UCC u. O t t tp =RC ln 3=1. 1 RC

Astable Multivibrator & Waveforms

2) Astable Multivibrator(Oscillator) 8 UCC 4 charge 5 K R 1 10 5 + + VA C 1 01 6 Q R D R 2 >2/3 <1/3 U UCC 5 K CC S D Q first 2 1 0 + + u. C=0 VB C 2 RD=1 + 7 u. C 5 K SD=0 – T . . . 1 discharge (grand) u. O 13

+VCC R 1 . R u. 2 C . C 5 8 4 6 3 2 71 u. C 2/3 UCC 1/3 UCC u. O tp 1 =(R 1+R 2)C ln 2=0. 7(R 1+R 2)C tp 2 =R 2 C ln 2=0. 7 R 2 C T=tp 1+tp 2 =0. 7(R 1+2 R 2)C Duty Cycle = tp 1/T t u. O tp 1 tp 2 What is an astable multivibrator? t

Applications using 555 timer A light dimmer ; n A car tachometer n Traffic Lights ; n Infra Red (IR) remote control ; n