Experiment 22 - 555 Mono Mv
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Transcript of Experiment 22 - 555 Mono Mv
9/16/2015
1
EXPERIMENT 22
555 MONOSTABLE
MULTIVIBRATOR (MV) Ferdinand M. Fernando
A s s t . P r o f e s s o r I
Logic Circuit F. M. Fernando URSM-College of Engineering 2
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Logic Circuit F. M. Fernando URSM-College of Engineering 3
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Logic Circuit F. M. Fernando URSM-College of Engineering 5
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PROCEDURE First, draw the circuit using your simulation software
(i.e. Ckt Wizard):
1. Run the simulation software.
2. Place the components and wire them together as
shown in the given circuit diagram.
3. Simulate the circuit & observe the signal indicated
by the logic probe when the Graph Window is
shown. What is the output signal and how much
output voltage is measured and for how long it is
ON? . . . . . . . . . . . . . . . . . . . . . . . . .
Logic Circuit F. M. Fernando URSM-College of Engineering 7
555 Monostable MV using Ckt Wizard
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4. Press and immediately release the push button
switch at the input to generate a pulse source
from the signal generator. Observe what happens
to the output signal as reflected by the two logic
probes. How much output voltage is measured
and for how long it was ON? . . . . . . . . . . . . . . . . .
5. Replace R3 (1 MΩ) with 2.2 MΩ. Press and
release immediately the input button again. What
does the signal probe indicate in terms of output
voltage and for how long it is ON? . . . . . . . . . . . .
Logic Circuit F. M. Fernando URSM-College of Engineering 9
6. State the difference between the result observed
between Procedure 4 & 5. . . . . . . . . . . . . . . . . . . . .
7. Calculate the period (T) using the formula
T=1.1RC and based from the measured values in
the previous steps, find the % accuracy of the
simulation using the absolute difference between
true and measured value divided by true value
and this result multiplied by 100%. . . . . . . . . . . . .
8. Using a stop watch (from your cell phone) verify
and compare the duration (T) of the 555’s ON
period in the previous steps. Again, measure the
software’s % accuracy. . . . . . . . . . . . . . . . . . . . . . .
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9. Using the formula for determining the ON
period of a 555 monostable MV, compute T
for the following RC combinations:
a) 4.7 MΩ & 1 µF, T =……….. d) 1 MΩ & 0.1 µF, T =……. .. ……
b) 2.2 MΩ & 0.47 µF, T =……. e) 560 KΩ & 0.1 µF, T =…………
c) 2.2 MΩ & 0.22 µF , T =…….
10.Draw the complete schematic diagram of a
555 monostable MV that generates a pulse
width of 1/2 second when it is triggered.
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WRITTEN REPORT
THE 74121 NONRETRIGGERABLE
ONE-SHOT
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NONRETRIGGERABLE ONE-SHOT ACTION
In the figure (a) is the nonretriggerable one-shot being
triggered at intervals greater than its pulse width and at
intervals less than the pulse width. Notice that in (a), the
additional pulses are ignored. Logic Circuit F. M. Fernando URSM-College of Engineering 13
LOGIC SYMBOLS FOR THE 74121 NONRETRIGGERABLE
The 74121 is an example of a nonretriggerable one-
shot IC. It has provisions for external R and C. The
inputs (A1 , A2 , & B) are gated trigger inputs. The
RINT input connects to a 2KΩ internal timing
resistor. Logic Circuit F. M. Fernando URSM-College of Engineering 14
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3 WAYS TO SET THE PULSE WIDTH OF A 74121 IC
When a 74121 receives a trigger signal on one of its trigger inputs Q goes HIGH, &
after a period of time determined by a resistor value and a capacitor value, the Q
output returns LOW (Q’ returns HIGH). The time that the outputs remain in their
triggered states is gives as tW = 0.7RC. Logic Circuit F. M. Fernando URSM-College of Engineering 15
PROBLEMS 1. A certain application requires the 74LS121 one-shot
with an output pulse width of 10 µs. Use an external C
in conjunction with RINT. Show the connections and
component values using the ANSI/IEEE std. symbol.
2. Using a simulation software, perform the following
laboratory procedures:
a) Calculate R needed to give an output pulse width of 600
µs with C equal to 0.1 µF.
b) Draw the schematic for a 74121 ckt. which uses these
values. Choose the trigger input which will cause the
74121 to be triggered on the rising edge of the trigger
signal. Show this on the Graph Window. Connect the
other trigger inputs to the proper logic levels so that
they are permanently enabled. Logic Circuit F. M. Fernando URSM-College of Engineering 16
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c) Simulate the circuit for a 1.2-kHz TTL-level square-wave signal to the trigger input.
d) Use a dual-trace scope to analyze and show the input and output signals.
e) If the output pulse width is not about 600 µs, change the value of R to correct it. Make sure you do not use a value lower than the specified minimum R value.
f) To demo that the 74121 circuit is nonretriggerable, you need to investigate its response with 3 different trigger frequencies. To start, draw a section of the input and output waveforms with the 1200-Hz trigger signal.
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g) Decrease the frequencies of the trigger signal to 500 Hz and draw a section of the trigger and the Q output waveforms.
h) Compare the width of the Q output pulse for a 500 Hz input signal with the Q output pulse width for the 1200-Hz trigger signal. Did the output high pulse width change as you went to a lower trigger frequency? Justify your answer by a graph of the signals.
i) Increase the frequency of the trigger signal to 2400 Hz and draw a section of the trigger and the Q output waveforms.
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j) Compare the width of the output pulse for this trigger signal with the output high pulse width for the previous cases.
k) Use the waveforms you drew for the 2400-Hz trigger signal to help you explain how a 74121 will respond to a trigger signal that occurs when the Q output is already high.
l) Compare the frequency of the output signal produced by a 1200-Hz trigger signal with the frequency of the output signal produced by a 2400-Hz trigger signal. Several applications of devices such as the 74121 take advantage of the frequency relationship you observe here.
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of Engineering 19