# Circuit Design and Analysis

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```					University of North Texas

EENG 2910
Circuit Design and
Analysis
Using SPICE
UK Traffic Light Controller
Team Members:
Tudor Nyawasha
Kodzo Agbedanu
Eric Ayeh
Group Members at duty

Eric,Ayeh from the left, Tudor
Nyawasha, Kodzo Agbedanu
Introduction (1)
As our final project for the spring
(2007),
semester (2007) we have to work on
a project of our choice that required
us to use the tools learned in this
course (EENG 2910): design simple
g
circuits containing: resistors,,
capacitors, inductors and voltage
sources using the PSpice software,
debug and test by the means of the
oscilloscope and all the equipments
laboratory
available in the laboratory.
Introduction (2)
Circuit operates red, amber & green
LEDs i          ifi
LED in a specific sequence
The UK traffic signal operates
differently from the one that we have
in the USA or in some other
countries. Below is the UK traffic
light sequence:
Red => red-amber => green =>amber
q
Sequence can be varied from 7s to
2.5 minutes
Components
Resistors: 470Ω x 3, 22kΩ, 100kΩ,
i bl
1MΩ variable
Caps: 0.1μF, 1μF, 10 μF
Diodes: 1N4148 x 6
red yellow
LEDs: red, yellow, green
555 timer IC
t
4017 counter IC
Major Components
555 timer IC
Used in astable mode
Provides clock pulse for 4017 counter
4017 counter IC
p    (Q     Q )
Has 10 outputs (Q0 to Q9)
Each output becomes high in turn as the
1MΩ variable resistor
Determines duration of complete
sequence
Purposes of main devices(1)
Use of a 555 timer circuit to produce
"clock" l      ( t bl     lti ib t )
" l k" pulses (astable multivibrator)
Use of a 4017 decade counter
circuit to produce a sequence of
pulses coming from the 555 and for
frequency division
p p
Diodes used in the purpose of
flashing sequences
Purposes of main devices(2)
IC outputs must not be directly
t d together
connected t    th
diodes can be used to combine two or
more digital outputs
y producing simple logic
Useful way of p        g     p    g
functions without using logic gates
we used 5 diodes to combine 5
outputs so that LED is ON for 5 clock
cycles
Components
Four our project, the main
t that          d d
components th t we needed were
fortunately available in the library of
PSpice
th software (PS i ) used. As a
the ft                       d A
matter of fact:
555 available in the ANL_MISC library
y just typing the
4017 IC is obtained by j       yp g
part name in the “part search
panel” available by clicking on the
p                  y        g
“place part” button.
555 circuit in PSpice
555 Component
For our project design, we did not
have to b ild the 555 ti
h      t build th                t bl
timer astable
oscillator as presented in the previous
lid W j t h          t    t the
slide. We just have to set th 555 i   in
the circuit and make sure that it
idi        t     t t
providing us at it output a square
wave that will represent the “clock”
i          i   t i t th
going as an input into the 4017 IC.IC
555 Astable Configuration
Vs

R1
0

8
U1
R2   2       VCC
4   TRIGGER         3    Output
5      OUTPUT
RESET
6   CONTROL
7   THRESHOLD
DISCHARGE
GND
1    555B
C1

0
555 Output in PSpice

0
2V

V
0

2V
-0
0s      0s
2m     0s
4m          6m
0s    0s
8m    0m
10s
(31
VR:)
ie
Tm
555 Astable Parameters
Frequency of output:
f = 1.4/ [C1(R1 + 2R2)]
Choosing R1, R2 & C1:
Choose C1 to suit the freq range
Choose R2 to give the freq required
i.e. R2 =0.7/(f × C1)
Choose R1 to be about a 1/10 of
R2 (1k min.)
555 Operation
C1 is charged by the current flowing
through R1 and R2.
th     h       d R2
When Vc reaches 2/3 of Vs (threshold
voltage) the output of the 555
becomes low
Capacitor discharges thru R2
When Vc reaches 1/3 of Vs (trigger
voltage) the output becomes high
This cycle repeats continuously
555 Output
Testing (555 & capacitors)
To make sure that in the designing of
i it        thi i       ki    i ht
our circuit everything is working right,
we have applied the “divide and
”     th d d t t the i it
conquer” method and test th circuit
at each level.
To process to the simulation, we have
used tools as the oscilloscope to test
the output of the 555 and the
capacitors.
Testing (555 & capacitors)
Results (using the oscilloscope).
Testing (555 & capacitors)
The outputs from the capacitors and
the      ti       ill t     h     i
th 555 timer oscillator as shown in
the figure obtained from the
ill                  t d W
oscilloscope are as expected. We can
therefore conclude that one part of
design i     ki
our d i is working properly. l
The 4017 Decade counter (1-of-10) is an useful electrical
device. It counts as the “clock” coming from the 555 timer
rising-edge)
output becomes high (on the rising edge). Each output from
Q0-Q9 goes high in turn as counting advances. For some
functions such as flash sequences (as in our project) outputs
may be combined using diodes.
The reset input should be low (0V) for normal operation
(counting 0-9). When high it resets the count to zero Q0
becomes therefore high. Counting to less than 9 is achieved
by connecting the relevant output (Q0-Q9) to reset, for
0,1,2,3                reset.
example to count 0 1 2 3 connect Q4 to reset
The disable input should be low (0V) for normal operation.
When high it disables counting so that the clock pulses are
ignored and the count is kept constant.
The ÷10 output is high for counts as 0-4 and low for 5-9,
so that it can provide an output at 1/10 of the clock
frequency. It is finally used here to drive the clock output
(
from the 555 timer (to count the tens). )
4017 Complete circuit
As we mentioned earlier, the PSpice
ft         t i in        f library
software contains i one of it lib
the device needed. Our designing was
th f        i lifi d i
therefore simplified since we did nott
have to redesign the complete circuit
in th fi             t di
as i the figure presented in one pff
the previous slides
counter from the 4000 series
p
takes clock pulses from
the (555) & makes ten
On
outputs come ‘On’ in
sequence
4017 Output Sequence
Only 1 output is
HIGH at a time
/    /
1/10 O/P is HIGH
for counts 0-4
& LOW for counts
5-9
4017 Output vs LED
Main Circuit Diagram
Simulation Result
6.0V

4.0V

2.0V

0V

-2.0V
0s              0.1s           0.2s           0.3s   0.4s   0.5s   0.6s   0.7s   0.8s   0.9s   1.0s
V(D10:1)    V(R6:1)   V(D9:1)    V(U1:OUTPUT)
Time
Simulation
The final simulations results obtained
PSpice
PS i were not really as expected.
t    ll          t d
To represent the LEDs in PSpice, we
d th di d D1N4148 W fi t
used the diodes D1N4148. We first
thought that we will obtain some
LEDs th t ill fl h i         i l ti
LED that will flash in our simulation
but it was not the case so we place
lt        k     t the i f
some voltage markers at th pin of
each diode to check it functionality
Final circuit Building
The simulations were not really
ti f i   H
satisfying. However, we process t  to
the designing of our circuit on the
l ti lb d O           th i it i
electrical board. Once the circuit is
built on the board, we connected the
lt              df t     t l the
voltage source and fortunately th
circuit was working almost as
t d
expected.
Final Circuit
Problems
The problems were various and at each
designing.
level of the designing First we encounter
some problems with the designing of the
main parts in the software and there
simulations (for example the LEDs). Also
after the designing of the final circuit, the
LEDs were taking too long to flash, we
then figured out that we need to “play”
ith th    l     f th   i bl      i t
with the value of the variable resistor till
we obtained the appropriate results.
Conclusion(1)
Appropriate outputs are combined
ith di d t       l th     ll
with diodes to supply the yellow &
green LEDs
Red LED is connected to the /10
output which saves having to use 5
diodes
p
Circuit worked as expected
Conclusion(2)
We have learned a lot through this
j t              d the bj ti
project course, and th objectives are
met. Even though we still have at
i t    h     id      t
some point an hazy idea or struggle l
with the designing of some circuits,
we now k           d d t dh
know and understand how
circuits are built, how the simulations
dh    th      lt
are run, and how the results are
obtained.
References
http://www.kpsec.freeuk.com/compo
t /    ht
nents/cmos.htm
http://www.doctronics.co.uk/4017.ht
m
Questions???

```
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