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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. 5.2 Draw a fully labelled circuit diagram of a sinking digital output. Indicate... 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.
Answer
A common cathode seven-segment LED display features segments (labeled a to g) that illuminate when positive voltage is applied to the relevant segment pins, while all cathodes of the LEDs are connected to ground. This configuration ensures that when a segment receives current, it lights up, displaying the corresponding decimal digit.
Step 2
Draw a fully labelled circuit diagram of a sinking digital output. Indicate the direction of current flow at the output.
Answer
The circuit diagram consists of a digital output connected to a transistor. When activated, the transistor allows current to flow from a positive voltage source through the load (like an LED) to ground. Current flows from the positive terminal through the load and into the transistor, demonstrating a sinking configuration.
Step 3
Explain the function of the encoder in FIGURE 5.3.
Answer
The encoder in FIGURE 5.3 is designed to convert the input signals from switches S1, S2, and S3 into a binary format. When a switch is activated, the encoder translates the corresponding decimal value of the active switch into a binary representation at outputs A0 and A1.
Step 4
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.
Answer
The logic circuit for the flip-flop consists of two AND gates and a NOR gate. The SET input connects to the AND gate, and the output connects to the NOR gate. The output of the NOR gate feeds back into the AND gates, allowing for flip-flop behavior.
Step 6
Draw the logic circuit of a half-adder using an AND gate and an Exclusive-OR gate.
Answer
The half-adder consists of two inputs A and B. The Exclusive-OR gate produces the sum (Σ), while the AND gate produces the carry output (Cₒ). The connection is direct from A and B to the respective gates.
Step 7
Step 8
Step 9
Explain the difference between the full-sequence counter and the truncated counter.
Answer
A full-sequence counter counts through its entire range before resetting, while a truncated counter is modified to stop counting before reaching its maximum count, potentially to simplify design or reduce the number of stages needed.
Step 10
Step 11
Refer to FIGURE 5.9 below and explain the sequential operation of this counter without the aid of a truth table.
Answer
In the counter shown in FIGURE 5.9, the clock signal triggers flip-flops FF0, FF1, and FF2 in sequence. As each flip-flop is activated, it passes its state to the next, creating a binary count. The feedback mechanism stops the counter when it reaches the count of 5 (binary 101) by disabling the first flip-flop, thereby preventing further counts.
Step 12
Draw a neatly labelled diagram of a four-bit serial-in: parallel-out shift register using D-type flip-flops.
Answer
The diagram consists of four D-type flip-flops connected in series, where the output of each flip-flop feeds into the input of the next. The serial data input connects to the first flip-flop, and parallel outputs are taken from each flip-flop to display the stored data.