4.1 State the light-altering principle of operation of the liquid crystal display (LCD) - NSC Electrical Technology Digital - Question 4 - 2019 - Paper 1
Question 4
4.1 State the light-altering principle of operation of the liquid crystal display (LCD).
4.2 With reference to encoders and decoders, answer the questions that fol... show full transcript
Worked Solution & Example Answer:4.1 State the light-altering principle of operation of the liquid crystal display (LCD) - NSC Electrical Technology Digital - Question 4 - 2019 - Paper 1
Step 1
State the light-altering principle of operation of the liquid crystal display (LCD).
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Answer
The liquid crystal display (LCD) operates on the principle of polarization. Liquid crystals manipulate light through variations in polarization, allowing control over the display's transparency or opacity in response to electric currents.
Step 2
Draw the circuit diagram of a simple two-digit-binary-input-to-four-digit-decimal-output decoder using TWO NOT gates and FOUR gates.
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Answer
To draw the circuit diagram, first represent the two binary inputs A and B. Use two NOT gates to invert these inputs. The outputs from the NOT gates, along with A and B, can then be used in a combination of AND and OR gates to create the four outputs which correspond to the decimal values.
Step 3
Complete the truth table of the two-digit-binary-input-to-four-digit-decimal-output decoder on the ANSWER SHEET FOR QUESTION 4.2.2.
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Answer
A
B
0
1
2
3
0
0
1
0
0
0
0
1
0
1
0
0
1
0
0
0
1
0
1
1
0
0
0
1
Step 4
Label input W.
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Answer
The input W is labeled corresponding to the input 'A' that serves as the enable input for the BCD-to-seven-segment decoder.
Step 5
Explain the function of the driver transistors found in the BCD-to-seven-segment display decoder.
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Answer
The driver transistors in the BCD-to-seven-segment decoder serve to provide sufficient current to drive each LED in the display. They ensure that each segment of the display is illuminated appropriately based on the BCD input.
Step 6
Complete the truth table of a BCD to seven-segment decoder connected to a seven-segment display in TABLE 4.3.3 on the ANSWER SHEET FOR QUESTION 4.3.3.
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Answer
BCD
a
b
c
d
e
f
g
0000
1
1
1
1
1
1
0
0001
0
1
1
0
0
0
0
0010
1
1
0
1
1
0
1
0011
1
1
1
1
0
0
1
0100
0
1
1
0
0
1
1
0101
1
0
1
1
0
1
1
0110
1
0
1
1
1
1
1
0111
1
1
1
0
0
0
0
1000
1
1
1
1
1
1
1
1001
1
1
1
0
0
1
1
Step 7
Draw the logic circuit of this half adder using an AND gate and an XOR gate.
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Answer
The logic circuit consists of an XOR gate that computes the sum (Σ), and an AND gate that computes the carry-out (C₀). The two inputs A and B are connected to both gates properly.
Step 8
Complete the truth table of this flip flop in TABLE 4.4.2 on the ANSWER SHEET FOR QUESTION 4.4.2.
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Answer
A
B
Σ
C₀
0
0
0
0
0
1
1
0
1
0
1
0
1
1
0
1
Step 9
Draw the logic circuit of this flip flop on the ANSWER SHEET FOR QUESTION 4.5.1, using NAND gates only.
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Answer
The RS flip flop can be drawn using two NAND gates, with the output of one connected to the input of the other, along with appropriate connections to the SET and CLR inputs.
Step 10
Complete the truth table of this flip flop in TABLE 4.5.2 on the ANSWER SHEET FOR QUESTION 4.5.2.
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Answer
CLK
S
R
Q
Q̄
0
0
0
0
1
0
0
1
0
1
0
1
0
1
0
0
1
1
1
0
1
X
X
0
1
(Where X indicates no change)
Step 11
Name TWO applications of counters.
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Answer
Frequency divider: Used in digital systems to reduce the frequency of a clock signal.
Decade counter: Used in devices that require counting up to ten and then resetting.
Step 12
Explain the operation of this counter.
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Answer
The asynchronous binary-to-BCD counter counts in binary and converts the binary output to BCD format. It employs flip flops that toggle based on clock pulses, where the output is derived from the Q states of these flip flops to represent decimal numbers.
