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4.1 Explain the term polarisation as used in the operation of a liquid crystal display (LCD.) 4.2 Refer to the LED seven-segment display and explain the difference between a common anode and a common cathode - NSC Electrical Technology Digital - Question 4 - 2019 - Paper 1
Question 4
4.1 Explain the term polarisation as used in the operation of a liquid crystal display (LCD.) 4.2 Refer to the LED seven-segment display and explain the difference ... show full transcript
Worked Solution & Example Answer:4.1 Explain the term polarisation as used in the operation of a liquid crystal display (LCD.) 4.2 Refer to the LED seven-segment display and explain the difference between a common anode and a common cathode - NSC Electrical Technology Digital - Question 4 - 2019 - Paper 1
Step 1
Explain the term polarisation as used in the operation of a liquid crystal display (LCD.)
Answer
Polarisation refers to the application of a polarising filter that allows light to vibrate in a single direction. In the context of liquid crystal displays (LCDs), the operation involves two layers of polarized glass. These layers allow the alignment or misalignment of the liquid crystals between them, enabling control over the passage of light. When electrical signals are applied, the orientation of the liquid crystals changes, affecting the light's polarization state and consequently the displayed image.
Step 2
Refer to the LED seven-segment display and explain the difference between a common anode and a common cathode.
Answer
In a common anode configuration, all the anodes of the LED segments are connected to a positive voltage source, while the cathodes are connected to the control logic. This means that to turn on a segment, the control logic must send a low signal to the corresponding cathode.
Conversely, in a common cathode configuration, all the cathodes are connected to ground (0 V), and the anodes are connected to the control logic. In this case, a segment is activated by sending a high signal to the corresponding anode. Thus, the main difference lies in where the common connection is made—at the anodes for the common anode display and at the cathodes for the common cathode display.
Step 3
Refer to FIGURE 4.3 below and determine the binary code at the output when the following input switches are pressed.
Answer
4.3.1 Switch 1: When Switch 1 is pressed, the output should be A0 = 1, indicating that the least significant bit is active.
4.3.2 Switch 5: When Switch 5 is pressed, it corresponds to A2 = 1 and A3 = 0. This combination represents the binary number for the activated switch.
4.3.3 Briefly describe the STATE of the input switches if all outputs are ZERO: If all outputs are ZERO, it means that none of the input switches are activated. Therefore, all input switches would be in the 'OFF' state.
Step 4
Study FIGURE 4.4 below of the logic circuit of a full adder using two half-adders and an OR-gate. Use the table on ANSWER SHEET 4.4 to complete the truth table.
Answer
The full adder truth table consists of inputs Ci (carry-in), A, and B, producing outputs for Sum and Co (carry-out). The truth table can be constructed based on the output logic of the half-adders and the OR gate logic:
| Ci | A | B | Sum | Co |
|---|---|---|---|---|
| 0 | 0 | 0 | 0 | 0 |
| 0 | 0 | 1 | 1 | 0 |
| 0 | 1 | 0 | 1 | 0 |
| 0 | 1 | 1 | 0 | 1 |
| 1 | 0 | 0 | 1 | 0 |
| 1 | 0 | 1 | 0 | 1 |
| 1 | 1 | 0 | 0 | 1 |
| 1 | 1 | 1 | 1 | 1 |
Step 5
Draw the logic circuit of this flip-flop using NAND gates, NOR gates and an inverter.
Answer
To draw the logic circuit of a D-type flip-flop, connect the D input to a NAND gate along with the CLK input. Use another NAND gate to combine the outputs from the first gate, introducing feedback loops where necessary. Additionally, utilize NOR gates to form the SR latch part of the flip-flop and place an inverter on the CLR line for output control.
Step 6