1. Multivibrator

2. Multivibrator
An electronic circuit used to implement a variety of simple two-state systems such as oscillators, timers and flip-flops.
Note:
Astable
Not stable in either state, switch from one state to other state continuously
Monostable
Which one of state s is stable , but other state is unstable
Bistable
Stable in either state, triggered by two external trigger

3. IC 555 - + Control Voltage (5) Threshold Voltage (6)
Trigger Voltage (2)
Ground (1)
Vcc (8)
Discharge (7)
Reset (4)
Output (3) - +
RESET
SET Q
COMP1
COMP2
Flip-Flop T1

4. Schematic of 555 RA RB C 5 Volts 3.333 V N/C Discharge 1.666 V Output
Threshold /
Trigger
Ground
Output
1.666 V
3.333 V RA RB C

5. 555 Timer Design Equations
Digital Electronics TM
1.2 Introduction to Analog
555 Timer Design Equations
tHIGH : Calculations for the Oscillator’s HIGH Time
The Output Is HIGH While The Capacitor Is Charging Through RA + RB. 5v
3.333 v Vc
1.666 v
0 v 
tHIGH 
Output
HIGH
LOW
Derivation of the equation for t-HIGH.
Project Lead The Way, Inc.
Copyright 2009

6. 555 Timer Design Equations
Digital Electronics TM
1.2 Introduction to Analog
555 Timer Design Equations
tLOW : Calculations for the Oscillator’s LOW Time
The Output Is LOW While The Capacitor Is Discharging Through RB. 5v
3.333 v Vc
1.666 v
0 v 
tLOW 
Output
HIGH
LOW
Derivation of the equation for t-LOW.
Project Lead The Way, Inc.
Copyright 2009

7. 555 Timer – Period / Frequency / DC
Digital Electronics TM
1.2 Introduction to Analog
555 Timer – Period / Frequency / DC
Period:
Duty Cycle:
Summary of a 555 time design equations.
Frequency:
Project Lead The Way, Inc.
Copyright 2009

8. Detail Analysis of a 555 Oscillator
555 Timer
Digital Electronics TM
1.2 Introduction to Analog
Detail Analysis of a 555 Oscillator 5v
3.333 v Vc
1.666 v
0 v
RESET
HIGH
LOW
SET T1 ON
OFF Q
Analysis of a 555 Oscillator: Slide 1 of 4
Project Lead The Way, Inc.
Copyright 2009

9. Detail Analysis of a 555 Oscillator
555 Timer
Digital Electronics TM
1.2 Introduction to Analog
Detail Analysis of a 555 Oscillator 5v
3.333 v Vc
1.666 v
0 v
RESET
HIGH
LOW
SET T1 ON
OFF Q
Analysis of a 555 Oscillator: Slide 2 of 4
Project Lead The Way, Inc.
Copyright 2009

10. Detail Analysis of a 555 Oscillator
555 Timer
Digital Electronics TM
1.2 Introduction to Analog
Detail Analysis of a 555 Oscillator 5v
3.333 v Vc
1.666 v
0 v
RESET
HIGH
LOW
SET T1 ON
OFF Q
Analysis of a 555 Oscillator: Slide 3 of 4
Project Lead The Way, Inc.
Copyright 2009

11. Detail Analysis of a 555 Oscillator
555 Timer
Digital Electronics TM
1.2 Introduction to Analog
Detail Analysis of a 555 Oscillator 5v
3.333 v Vc
1.666 v
0 v
RESET
HIGH
LOW
SET T1 ON
OFF Q
Output Is HIGH While The Capacitor Is Charging Through RA + RB.
Output Is LOW While The Capacitor Is Discharging Through RB.
Analysis of a 555 Oscillator: Slide 4 of 4
Project Lead The Way, Inc.
Copyright 2009

12. Improved 555 Duty Cycle
By connecting this diode, D1 between the trigger input and the discharge input, the timing capacitor will now charge up directly through resistor R1 only, as resistor R2 is effectively shorted out by the diode. The capacitor discharges as normal through resistor, R2.
Now the previous charging time of t1 = 0.693(R1 + R2)C is modified to take account of this new charging circuit and is given as: 0.693(R1 x C). The duty cycle is therefore given as D = R1/(R1 + R2). Then to generate a duty cycle of less than 50%, resistor R1 needs to be less than resistor R2.

13. Multivibrator Circuit using 555

14. Circuit Diagram
R = 10k
C = 0.1 uF
74HC14 Hex-Inverter Schmitt-Trigger

15. Circuit Diagram C = 560 pF RA and RB  RA > RB RA = RB RA < RB
With dioda 1N 4148 (improve duty cycle