RELAX AND ENJOY THE PRESENTATION TOGETHER

OBJECTIVES Students should be able to draw the circuit of a monostable multivibrator using IC 555 explain the operation of the monostable multivibrator calculate the time delay using the formula t = 1.1 RC

INTRODUCTION To achieve these objectives IC 555 configure it as a monostable multivibrator analyse the output waveform explain the operation calculate the time delay

ELECTRONIC TIMER COMMERCIALLY THERE ARE TWO TYPE OF ELECTRONIC TIMERS 555 TIMER 556 TIMER (TWO 555 TIMERS)

FACTS ABOUT 555 TIMER It is an 8 pin Integrated Circuit It is available in DIP It can be configured to act as astable multivibrator monostable multivibrator

PIN CONFIGURATION OF THE 555 TIMER GROUND TRIGGER OUTPUT RESET CONTROL VOLTAGE THRESHOLD DISCHARGE V cc

WHAT IS A MONOSTABLE MULTIVIBRATOR IT IS A ONE - SHOT MULTIVIBRATOR. OUTPUT VOLTAGE WILL SWITCH FROM ITS LOW ‘0’ STATE TO THE HIGH ‘1’ STATE WHEN A NEGATIVE PULSE IS APPLIED.

WHAT IS A MONOSTABLE MULTIVIBRATOR IT WILL REMAIN HIGH FOR A SHORT DURATION. THE ‘HIGH’ DURATION DEPENDS ON THE EXTERNAL RESISTOR AND CAPACITOR. AT THE END OF THE DURATION, THE OUTPUT RETURNS TO ITS LOW STATE.

WHAT IS A MONOSTABLE MULTIVIBRATOR BASED ON THE CONDITION EXPLAINED, WHAT DO YOU THINK THE OUTPUT OF A MONOSTABLE VIBRATOR SHOULD BE

WHAT IS A MONOSTABLE MULTIVIBRATOR THE OUTPUT OF A MONOSTABLE MULTIVIBRATOR SHOULD BE Trigger input Output

WHAT IS A MONOSTABLE MULTIVIBRATOR THE OUTPUT OF A MONOSTABLE MULTIVIBRATOR SHOULD BE Trigger input Output t

V R C Output Trigger input FF 0.01 CONFIGURING 555 AS A MONOSTABLE MULTIVIBRATOR

CONFIGURING THE 555 AS A MONOSTABLE MULTIVIBRATOR I NEED RESISTOR AND CAPACITOR TO CONFIGURE THE 555 TIMER AS A MONOSTABLE MULTIVIBRATOR.

CONFIGURING THE 555 AS A MONOSTABLE MULTIVIBRATOR I NEED RESISTOR AND CAPACITOR TO CONFIGURE THE 555 TIMER AS A MONOSTABLE MULTIVIBRATOR. IT’S SO SIMPLE

CONFIGURING THE 555 AS A MONOSTABLE MULTIVIBRATOR I NEED RESISTOR AND CAPACITOR TO CONFIGURE THE 555 TIMER AS A MONOSTABLE MULTIVIBRATOR.

CONFIGURING THE 555 AS A MONOSTABLE MULTIVIBRATOR I NEED RESISTOR AND CAPACITOR TO CONFIGURE THE 555 TIMER AS A MONOSTABLE MULTIVIBRATOR. IT’S SO SIMPLE

CONFIGURING THE 555 AS A MONOSTABLE MULTIVIBRATOR I NEED RESISTOR AND CAPACITOR TO CONFIGURE THE 555 TIMER AS A MONOSTABLE MULTIVIBRATOR.

CONFIGURING THE 555 AS A MONOSTABLE MULTIVIBRATOR I NEED RESISTOR AND CAPACITOR TO CONFIGURE THE 555 TIMER AS A MONOSTABLE MULTIVIBRATOR. IT’S SO SIMPLE

OUTPUT OF MONOSTABLE MULTIVIBRATOR V R C FF 0.01 Trigger input Output t

OUTPUT WAVEFORM Trigger input Output stays low until the trigger input goes low 0

OUTPUT WAVEFORM Trigger input Output stays low until the trigger input goes low 0

OUTPUT WAVEFORM Trigger input Output stays low until the trigger input goes low 0

OUTPUT WAVEFORM Trigger input Output stays low until the trigger input goes low 0

OUTPUT WAVEFORM Trigger input Output stays low until the trigger input goes low 0

OUTPUT WAVEFORM Trigger input 0 Output stays low until the trigger input goes low Trigger input goes low, output goes high

OUTPUT WAVEFORM Trigger input 0 Output stays low until the trigger input goes low Trigger input goes low, output goes high

OUTPUT WAVEFORM Trigger input 0 Output stays low until the trigger input goes low Trigger input goes low, output goes high

OUTPUT WAVEFORM Trigger input 0 Output stays low until the trigger input goes low Trigger input goes low, output goes high

OUTPUT WAVEFORM Trigger input 0 Output stays low until the trigger input goes low Trigger input goes low, output goes high

OUTPUT WAVEFORM Output stays low until the trigger input goes low Trigger input goes low, output goes high At this point, the output will remain high Trigger input 0

OUTPUT WAVEFORM Output stays low until the trigger input goes low Trigger input goes low, output goes high At this point, the output will remain high Trigger input 0

OUTPUT WAVEFORM Output stays low until the trigger input goes low Trigger input goes low, output goes high At this point, the output will remain high Trigger input 0

OUTPUT WAVEFORM Output stays low until the trigger input goes low Trigger input goes low, output goes high At this point, the output will remain high Trigger input 0

OUTPUT WAVEFORM Output stays low until the trigger input goes low Trigger input goes low, output goes high At this point, the output will remain high Trigger input 0

OUTPUT WAVEFORM Output stays low until the trigger input goes low Trigger input goes low, output goes high At this point, the output will remain high The period of time is determined by the value of the RC network t Trigger input 0

OUTPUT WAVEFORM Output stays low until the trigger input goes low Trigger input goes low, output goes high At this point, the output will remain high The period of time is determined by the value of the RC network Trigger input 0

OUTPUT WAVEFORM Output stays low until the trigger input goes low Trigger input goes low, output goes high At this point, the output will remain high The period of time is determined by the value of the RC network t Trigger input 0

OUTPUT WAVEFORM Output stays low until the trigger input goes low Trigger input goes low, output goes high At this point, the output will remain high The period of time is determined by the value of the RC network Trigger input 0

OUTPUT WAVEFORM Output stays low until the trigger input goes low Trigger input goes low, output goes high At this point, the output will remain high The period of time is determined by the value of the RC network t Trigger input 0

RELAX TIME We shall now take a short break to recapitulate what we had been studying so far

LET’S CONTINUE We have seen the output of the monostable multivibrator We will now take a step further by looking into the constructional features of the 555 timer

CAN YOU REMEMBER WHAT YOU HAVE SEEN ?

CAN YOU REMEMBER WHAT YOU HAVE SEEN ? 555 TIMER

CAN YOU REMEMBER WHAT YOU HAVE SEEN ?

R R R R C S R Q Vc c BLOCK DIAGRAM comparators

R R R R C + 2 _ + 1 _ S R Q Vc c BLOCK DIAGRAM RS flip flop

R R R R C + 2 _ + 1 _ Vc c BLOCK DIAGRAM RS flip flop

R R R R C + 2 _ + 1 _ S R Q Vc c BLOCK DIAGRAM transistor

R R R R C + 2 _ + 1 _ S R Q Vc c BLOCK DIAGRAM transistor

R R R R C + 2 _ + 1 _ S R Q Vc c BLOCK DIAGRAM inverter buffer

R R R R C + 2 _ + 1 _ S R Q Vc c BLOCK DIAGRAM inverter buffer

R R R R C + 2 _ + 1 _ S R Q Vc c BLOCK DIAGRAM inverter buffer

R R R R C + 2 _ + 1 _ S R Q Vc c BLOCK DIAGRAM inverter buffer

R R R R C + 2 _ + 1 _ S R Q Vc c BLOCK DIAGRAM inverter buffer

OPERATION + 2 _ + 1 _ S R Q _ __ 1 0 S R Q 0 0 Q

OPERATION + 2 _ + 1 _ S R Q 0 S R Q 0 0 Q __

+ 2 _ + 1 _ S R Q OPERATION __ S R Q 0 0 Q

+ 2 _ + 1 _ S R Q OPERATION __ S R Q 0 0 Q

CALCULATION OF TIME DELAY THE TIME DELAY t = 1.1 R C where R = resistance (ohm) C = capacitance (farad)

CALCULATION OF TIME DELAY The time delay depends on the external resistor and capacitor C varies from 0.01 uF to 100uF R varies from 1 Kohm to 10 Mohm With this RC combination, the timer would be able to give a time delay of 0.01 msec to 1100 secs.

EXAMPLE Calculate the time delay of the monostable multivibrator if R = 1 kohm and C = 0.1 uF

SOLUTION R = 1 x 10 3 ohm C = 0.1 x farad t = 1.1 RC = 1.1 x 1 x 10 3 x 0.1 x = 110 x seconds Time delay is 110 us

TUTORIAL Calculate the time delay of the monostable multivibrator if R = 10 kohm and C = 10 uF R = 100 kohm and C = 1 uF R = 1Mohm and C = 0.1 uF

R R R R C + 2 _ + 1 _ S R Q Vcc BLOCK DIAGRAM 3 4

PROGRESS TEST 1.IC 1 and IC 2 function as A)comparators B)differentiators C)flip flop D)inverter buffer

PROGRESS TEST 2.IC 3 is a A)counter B)flip flop C)shift register D)inverter buffer

PROGRESS TEST 3.When the power is switched on, comparator 2 will be driven A)high B)low C)unstable D)stable

PROGRESS TEST 4.During the unstable state, the output of the monostable multivibrator is A)high B)low C)unstable D)stable

PROGRESS TEST 5.The time delay of the monostable multivibrator is affected by A)comparators B)inverter buffer C)flip flop D)RC network

PROGRESS TEST 6.The output of the monostable multivibrator is pin A)1 B)2 C)3 D)8

PROGRESS TEST 7.The Vcc of the monostable multivibrator is pin A)1 B)2 C)3 D)8

PROGRESS TEST 8.The trigger input of the monostable multivibrator is pin A)1 B)2 C)3 D)8

PROGRESS TEST 9.The pin that is connected to ground is pin A)1 B)2 C)3 D)4

PROGRESS TEST 10.The external resistor is connected between Vcc and pin A)1 B)2 C)7 D)8

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