5.1 Explain the term common cathode with reference to the seven-segment LED display - NSC Electrical Technology Digital - Question 5 - 2021 - Paper 1
Question 5
5.1 Explain the term common cathode with reference to the seven-segment LED display.
A common cathode seven-segment LED display is a type of display where all the c... show full transcript
Worked Solution & Example Answer:5.1 Explain the term common cathode with reference to the seven-segment LED display - NSC Electrical Technology Digital - Question 5 - 2021 - Paper 1
Step 1
Explain the term common cathode with reference to the seven-segment LED display.
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Answer
A common cathode seven-segment LED display is a type of display where all the cathodes of the LED segments are connected together to a common ground. In this configuration, the individual segments illuminate when a positive voltage is applied to the anodes.
Step 2
Draw a fully labelled circuit diagram of a sinking digital output. Indicate the direction of current flow at the output.
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Answer
The diagram should show a typical NPN transistor connected to an LED where the collector connects to the load (in this case, the LED) and the emitter to ground. The input to the base is provided through a resistor to control the current. The direction of current flow is from the collector to the emitter when the transistor is activated.
Step 3
Explain the function of the encoder in FIGURE 5.3.
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The encoder in FIGURE 5.3 takes multiple input lines (S1, S2, S3) and converts the active input into a unique binary output represented at the outputs A0 and A1. It effectively compresses the information coming from several input signals into a binary representation.
Step 4
Complete the logic state of inputs and outputs in boxes A to E on the ANSWER SHEET for QUESTION 5.2 when S1 is pressed.
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When S1 is pressed, the outputs A0 and A1 will assume the state corresponding to the binary representation of the active input signal S1. For a typical 3-to-2 encoder, it would output (0, 0) for S1.
Step 5
Draw the labelled logic circuit for the logic symbol in FIGURE 5.4 using AND gates and NOR gates only on the ANSWER SHEET for QUESTION 5.4.
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The logic circuit should represent a flip-flop using two NOR gates and including connections for the SET and RESET inputs.
Step 6
Draw the logic circuit of a half-adder using an AND gate and an Exclusive-OR gate.
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The half-adder circuit consists of one Exclusive-OR gate to represent the Sum output and an AND gate to represent the Carry output of the two inputs A and B.
Step 7
Complete the truth table of the half-adder in the table (X, Y and Z) on the ANSWER SHEET for QUESTION 5.5.2.
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The truth table indicates all possible combinations of inputs A and B along with the corresponding Sum and Carry outputs.
Step 8
Name TWO applications of counters.
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Counters can be used as frequency dividers and for counting pulses in digital applications.
Step 9
Explain the difference between the full-sequence counter and the truncated counter.
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A full-sequence counter increments its output for every clock pulse until it reaches its maximum count, representing all possible states. A truncated counter, however, is designed to stop counting before reaching its maximum state.
Step 10
Explain the term positive edge triggering.
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Positive edge triggering occurs when a digital circuit responds to the leading edge of a pulse signal, detecting the moment the signal transitions from low to high.
