NSC Electrical Technology Electronics Waveforms, flowcharts, circuits: 5.1 Explain the difference betwe

Question

5.1 Explain the difference between a common anode and a common cathode.

A common anode display connects all anodes of the LED segments to a single positive voltage source. Each LED segment is turned on by applying a low voltage at the corresponding cathode. In contrast, a common cathode display connects all cathodes to ground, and a high voltage is applied to the anode to illuminate segments.

5.1.2 State TWO methods that use transistors to connect the power supply to the seven-segment display.

1. **Transistor Switch Configuration**: In this method, transistors are used as switches. When a certain base current is applied, the transistor allows current to flow from the collector to the emitter, powering the respective segment of the display.

2. **Darlington Pair Configuration**: This involves using two transistors to amplify the current driving the seven-segment display. It ensures that even with a small input current, the segments can receive sufficient current to light up.

5.2 Refer to FIGURE 5.2 of a decimal-to-binary encoder below and answer the questions that follow.

5.2.1 State the typical voltage levels at X and Y.

X: Logic High (typically +5V)
Y: Logic Low (typically 0V)

5.2.2 Determine the binary code at the output when switch 9 is pressed.

When switch 9 is pressed, the binary output would be 1001, representing the decimal value 9.

5.2.3 Describe how a coherent picture is created on an LCD screen.

A coherent picture on an LCD screen is created by controlling the light passing through liquid crystals via a matrix of pixels. Each pixel can be made to appear bright or dark depending on the applied voltage, with varying levels of intensity that create the desired color and brightness for the entire image.

5.4 Determine the sum produced by the three-bit parallel adder in FIGURE 5.4 when the binary numbers 111 and 101 are added together, completing boxes A2 A1 A0 and B2 B1 B0.

A2 A1 A0 = 111
B2 B1 B0 = 101

The sum is calculated as follows:

$$	ext{Sum} = (111 + 101)_{2} = 1100_{2}$$

Where the sum can be organized as:

- A2 = 1
- A1 = 1
- A0 = 0
- Carry = 1

5.5 Refer to FIGURE 5.5 of the clocked RS-type flip-flop and answer the questions that follow.

5.5.1 Complete the logic circuit diagram of this flip-flop on ANSWER SHEET 5.1.

5.5.2 Determine the output at Q by completing the timing diagrams on ANSWER SHEET 5.2. Assume Q starts LOW.

If the clock pulse transitions as follows:

- From LOW to HIGH: The output Q changes based on the inputs S and R according to the flip-flop behavior.

5.6 State the function of a decoder.

A decoder is a combinational logic circuit that converts binary data into a unique output. Each combination of the input lines activates a single output line, making it useful for memory address decoding and data demultiplexing.

5.7 Name ONE example of EACH of the following categories of flip-flops.

5.7.1 Asynchronous: Toggle Flip-Flop

5.7.2 Synchronous: D Flip-Flop

5.8 Explain the following terms with reference to memory elements.

5.8.1 Negative edge triggering: This refers to a type of triggering where a flip-flop responds to a change in input signal at the falling edge, enhancing synchronization in digital circuits.

5.8.2 Propagation delay: The time taken for an input change to affect the output of a flip-flop, which is crucial in timing analysis for circuit designs.

5.9 Briefly describe the following counters.

5.9.1 Truncated counter: A counter that stops counting before it reaches its maximum count, often used to reduce the number of flip-flops needed.

5.10 Refer to FIGURE 5.10 of a counter and answer the questions that follow.

5.10.1 Identify the circuit in FIGURE 5.10.

This circuit is a binary counter.

5.10.2 Explain how the counter will be enabled to count either up or down when the input is high.

When the input is high, the control logic determines the direction of counting by activating either the up-counting or down-counting flip-flops accordingly.

5.11 Refer to FIGURE 5.11 below and answer the questions that follow.

5.11.1 Identify the register in 5.11.

The register is a shift register used for temporary data storage.

5.1 Explain the difference between a common anode and a common cathode - NSC Electrical Technology Electronics - Question 5 - 2023 - Paper 1

Worked Solution & Example Answer:5.1 Explain the difference between a common anode and a common cathode - NSC Electrical Technology Electronics - Question 5 - 2023 - Paper 1

5.1 Explain the difference between a common anode and a common cathode.

5.1.2 State TWO methods that use transistors to connect the power supply to the seven-segment display.

5.2.1 State the typical voltage levels at X and Y.

5.2.2 Determine the binary code at the output when switch 9 is pressed.

5.2.3 Describe how a coherent picture is created on an LCD screen.

5.4 Determine the sum produced by the three-bit parallel adder in FIGURE 5.4 when the binary numbers 111 and 101 are added together.

5.5.1 Complete the logic circuit diagram of this flip-flop on ANSWER SHEET 5.1.

5.5.2 Determine the output at Q by completing the timing diagrams on ANSWER SHEET 5.2.

5.6 State the function of a decoder.

5.7.1 Name ONE example of EACH of the following categories of flip-flops: Asynchronous.

5.7.2 Name ONE example of EACH of the following categories of flip-flops: Synchronous.

5.8.1 Explain negative edge triggering.

5.8.2 Explain propagation delay.

5.9.1 Briefly describe a truncated counter.

5.10.1 Identify the circuit in FIGURE 5.10.

5.10.2 Explain how the counter will be enabled to count either up or down when the input is high.

5.11.1 Identify the register in 5.11.

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