Electrical Technology Grade 12 NSC June 2022 QP (Eng)

Downloaded from hlayiso.com SENIOR CERTIFICATE EXAMINATIONS/ NATIONAL SENIOR CERTIFICATE EXAMINATIONS ELECTRICAL TECHNOLOGY: DIGITAL ELECTRONICS 2022 MARKS: 200 TIME: 3 hours This question paper consists of 17 pages, a 1-page formula sheet and 9 answer sheets. Copyright reserved Please turn over

Downloaded from hlayiso.com Electrical Technology: Digital Electronics 2 DBE/2022 SC/NSC INSTRUCTIONS AND INFORMATION 1. This question paper consists of SIX questions. 2. Answer ALL the questions. 3. Answer the following questions on the attached ANSWER SHEETS: QUESTIONS 3.3.5, 3.4.6, 3.6.1 and 3.6.2 QUESTION 4.2.3 QUESTIONS 5.3.1, 5.4.1, 5.4.2, 5.5, 5.6.1 and 5.8 QUESTION 6.11 4. Write your centre number and examination number on every ANSWER SHEET and hand them in with your ANSWER BOOK, whether you have used them or not. 5. Sketches and diagrams must be large, neat and FULLY LABELLED. 6. Show ALL calculations and round off answers correctly to TWO decimal places. 7. Number the answers correctly according to the numbering system used in this question paper. 8. You may use a non-programmable calculator. 9. Calculations must include: 9.1 Formulae and manipulations where needed 9.2 Correct replacement of values 9.3 Correct answer and relevant units where applicable 10. A formula sheet is attached at the end of this question paper. 11. Write neatly and legibly. Copyright reserved Please turn over

Downloaded from hlayiso.com Electrical Technology: Digital Electronics 3 DBE/2022 SC/NSC QUESTION 1: MULTIPLE-CHOICE QUESTIONS Various options are provided as possible answers to the following questions. Choose the answer and write only the letter (AD) next to the question numbers (1.1.1 to 1.1.15) in the ANSWER BOOK, e.g. 1.16 D. 1.1 The layer(s) of the skin that is/are affected by a third-degree burn would be … A the outer layer. B the second layer. C all layers of the skin. D None of the above-mentioned. (1) 1.2 A/An … circuit is used to clean up an input signal which has been distorted. A integrator B differentiator C Schmitt trigger D comparator (1) 1.3 Open-loop gain with reference to op amps is when … A a feedback resistor is connected from the output to the inverting input. B no feedback resistor is connected from the output to the input. C a capacitor is connected from the output to the inverting input. D a feedback resistor is connected from the output to the non-inverting input. (1) 1.4 When a triangular waveform is applied to the input of a differentiator, the output waveform will be a/an … A DC level. B inverted triangular waveform. C first harmonic frequency of the triangular waveform. D square waveform. (1) 1.5 The basic circuit of a passive RC differentiator is a … A capacitor in series with the input and a resistor in parallel with the output. B resistor in series with the input and a capacitor in parallel with the output. C resistor in series with the input and a resistor in parallel with the output. D capacitor in series with the input and a capacitor in parallel with the output. (1) Copyright reserved Please turn over

Downloaded from hlayiso.com Electrical Technology: Digital Electronics 4 DBE/2022 SC/NSC 1.6 Phase shift through an op amp is caused by the … A cut-off frequency. B internal RC circuits. C notch frequency. D unity-gain frequency. (1) 1.7 Negative feedback in an op amp … A increases the input and output impedances. B decreases the output impedance and the bandwidth. C increases the input impedance and the bandwidth. D does not affect impedances or the bandwidth. (1) 1.8 A … output is the transistor collector connected to the cathode of the LED. A sourcing B draining C distributing D sinking (1) 1.9 The … is designed to accept input data in decimal form and convert this information into its binary form. A decoder B seven-segment display C encoder D half-adder (1) 1.10 A combinational logic circuit combining an AND gate with an exclusive OR gate (XOR) is called the … circuit. A half-adder B full adder C parallel adder D arithmetic (1) 1.11 The … is where the timing signal is delayed by a fraction of time through each flip-flop. A ripple counter B down counter C frequency divider D propagation delay (1) Copyright reserved Please turn over

Downloaded from hlayiso.com Electrical Technology: Digital Electronics 5 DBE/2022 SC/NSC 1.12 A fast temporary memory that allows information to be stored and retrieved by the system as it operates, is called the … A ROM. B RAM. C CPU. D I/O unit. (1) 1.13 A register that contains the address and status of the next instruction for processing and also tells the processor what the next instruction is, is called the … A program counter. B memory address register. C accumulator. D current instruction register. (1) 1.14 The bus that is used to transmit the memory address from the memory and input/output ports to the CPU is called the … bus. A system B control C data D address (1) 1.15 ONE advantage of the serial peripheral interface bus (SPI) is that it … A cannot transmit off the PCB. B is susceptible to noise. C supports high-speed full-duplex communication. D supports only one master device on the bus. (1) [15] Copyright reserved Please turn over

Downloaded from hlayiso.com Electrical Technology: Digital Electronics 6 DBE/2022 SC/NSC QUESTION 2: OCCUPATIONAL HEALTH AND SAFETY 2.1 Explain the term machinery with reference to the Occupational Health and Safety Act, 1993 (Act 85 of 1993). (2) 2.2 Explain the term critical incident with regard to emergencies. (2) 2.3 State TWO steps you should take when you discover a fire in an electrical workshop. (2) 2.4 State the importance of wearing a face mask in the workshop. (2) 2.5 Name TWO environmental considerations when working with chemicals during the printed circuit board manufacturing process. (2) [10] Copyright reserved Please turn over

Downloaded from hlayiso.com Electrical Technology: Digital Electronics 7 DBE/2022 SC/NSC QUESTION 3: SWITCHING CIRCUITS 3.1 Name the type of multivibrator that: 3.1.1 Produces one pulse cycle of 'high' and 'low' when a trigger pulse is applied to its input (1) 3.1.2 Changes state when a trigger pulse is applied and remains in that state (1) 3.2 Refer to FIGURE 3.2 below and answer the questions that follow. +9V R2 R1 10 kΩ 10 kΩ R3 4 8 470 Ω 7 555 3 6 2 1 5 LED Set Reset C1 10 nF FIGURE 3.2: BI-STABLE MULTIVIBRATOR 3.2.1 Name the function of resistors: (a) R1 (1) (b) R3 (1) 3.2.2 Identify the state of the LED when trigger pin 2 is high. (1) 3.2.3 Explain what happens in the circuit when the set switch is pressed. (2) 3.2.4 Explain the purpose of connecting pin 6 to ground. (2) Copyright reserved Please turn over

Downloaded from hlayiso.com Electrical Technology: Digital Electronics 8 DBE/2022 SC/NSC 3.3 FIGURE 3.3 below shows an op amp as a comparator. The resistance of the LDR increases as the level of light falls. +V R1 V Vin 100 kΩ R3 Vref 1 kΩ 741 t R2 100 kΩ LED 2 LDR LED 1 white red 0V -V FIGURE 3.3: OP AMP COMPARATOR AS A DARK SENSOR 3.3.1 State the purpose of R2. (1) 3.3.2 Explain how an increase in the level of light affects the voltage on the non-inverting input. (2) 3.3.3 Explain the operation of the circuit with reference to the voltages on the input terminals and the output voltage. (3) 3.3.4 Predict the state of LED1 and LED2 when the voltage on the inverting terminal is higher than the voltage on the non-inverting terminal. (2) 3.3.5 Draw the output on the ANSWER SHEET for QUESTION 3.3.5. (3) Copyright reserved Please turn over

Downloaded from hlayiso.com Electrical Technology: Digital Electronics 9 DBE/2022 SC/NSC 3.4 Refer to FIGURE 3.4 below and answer the questions that follow. VIN +10 V V 0 t VOUT RF -10 V 9 kΩ 1V 0 t R1 -1 V 1 kΩ 0V FIGURE 3.4: SCHMITT TRIGGER 3.4.1 Identify the type of Schmitt trigger circuit. (1) 3.4.2 Determine the value of the output voltage when the voltage on the non-inverting input is -1 V. (1) 3.4.3 State whether this circuit uses positive or negative feedback. (1) 3.4.4 Explain the operation of the circuit with reference to the input and trigger voltage levels. (4) 3.4.5 Predict how an increase in the value of R1 will affect the trigger voltage level. (1) 3.4.6 Draw the output signal on the ANSWER SHEET for QUESTION 3.4.6. (4) Copyright reserved Please turn over

Downloaded from hlayiso.com Electrical Technology: Digital Electronics 10 DBE/2022 SC/NSC 3.5 Refer to FIGURE 3.5 below and answer the questions that follow. RF 100 kΩ C1 R1 10 kΩ 0,4 V C2 R2 10 kΩ +9 V 0,5 V - C3 R3 10 kΩ + 0,25 V VOUT -9 V 0V FIGURE 3.5: SUMMING AMPLIFIER 3.5.1 The variable resistor RF serves a dual purpose. Name both purposes. (2) 3.5.2 Calculate the output voltage when the value of RF is set to 78,26 kΩ. (3) 3.5.3 Explain how an increase in the value of RF affects the gain of the amplifier. (1) 3.5.4 Describe why it is not recommended to increase the value of RF beyond 78,26 kΩ. (4) 3.5.5 Explain how this limitation can be overcome without changing the value of any of the resistors. (2) 3.6 Refer to FIGURE 3.6 below and answer the questions that follow. V R 1 kΩ Input VIN VOUT t Vsupply C Output 10 µF t FIGURE 3.6: PASSIVE RC INTEGRATOR 3.6.1 Draw the output when the value of C is changed to 1 µF on the ANSWER SHEET for QUESTION 3.6.1. (3) 3.6.2 Draw the output when the value of C is changed to 100 µF on the ANSWER SHEET for QUESTION 3.6.2. (3) [50] Copyright reserved Please turn over

Downloaded from hlayiso.com Electrical Technology: Digital Electronics 11 DBE/2022 SC/NSC QUESTION 4: SEMICONDUCTOR DEVICES 4.1 FIGURE 4.1 below shows the 555 IC. Answer the questions that follow. 0V 1 8 +Vcc TRIGGER 2 7 DISCHARGE 555 IC OUTPUT 3 6 THRESHOLD CONTROL RESET 4 5 VOLTAGE FIGURE 4.1: 555 IC PIN LAYOUT 4.1.1 Briefly describe the functions of pin 6 with reference to the 555 IC. (3) 4.1.2 State the supply voltage range at which the 555 IC operates. (2) 4.1.3 Explain the function of the SR flip-flop in the internal circuit of the 555 timer. (2) Copyright reserved Please turn over

Downloaded from hlayiso.com Electrical Technology: Digital Electronics 12 DBE/2022 SC/NSC 4.2 Refer to FIGURE 4.2 below and answer the questions that follow. Vcc = +5 V to 15 V R1 R2 8 4 Vout 7 3 555 IC 6 1 2 0 5 1 Trigger Input C1 C = 0,01 µF (S1) 0V FIGURE 4.2: 555 IC MULTIVIBRATOR 4.2.1 Identify the multivibrator in FIGURE 4.2. (1) 4.2.2 Give a brief description of what happens when the push-to-make switch (S1) is activated. (4) 4.2.3 Draw on the ANSWER SHEET for QUESTION 4.2.3 the voltage waveform of the capacitor C1 and the output voltage waveform when the trigger input is pressed. (4) Copyright reserved Please turn over

Downloaded from hlayiso.com Electrical Technology: Digital Electronics 13 DBE/2022 SC/NSC 4.3 Refer to the astable multivibrator in FIGURE 4.3 below which has an output frequency of 1 hertz. Answer the questions that follow. 9V R1 4 8 7 3 Vout 555 f = 1 Hz R2 R3 6 2 1 5 LED C1 C2 0V FIGURE 4.3: ASTABLE MULTIVIBRATOR 4.3.1 Explain the mode (state) of the LED. (2) 4.3.2 Explain the effect on the LED when: (a) R2 is halved (1) (b) The value of C1 is doubled (1) [20] Copyright reserved Please turn over

Downloaded from hlayiso.com Electrical Technology: Digital Electronics 14 DBE/2022 SC/NSC QUESTION 5: DIGITAL AND SEQUENTIAL DEVICES 5.1 Answer the following questions with reference to the seven-segment LED display. 5.1.1 Describe the difference between common-anode and common- cathode connections. (2) 5.1.2 Draw the circuit of a sourcing digital output using an LED and a transistor. Indicate the direction of current flow at the output. (5) 5.2 Refer to FIGURE 5.2 below and answer the questions that follow. Grid A Grid B Rotated 90º Radiating light FIGURE 5.2: POLARISING GRIDS 5.2.1 Explain the process when light waves pass through grid A. (2) 5.2.2 State the effect that grid B has on the light waves. (1) 5.3 Answer the following questions with reference to encoders and decoders. 5.3.1 Complete the circuit diagram of a three-digit decimal input to two-bit binary output encoder on the ANSWER SHEET for QUESTION 5.3.1. (6) Copyright reserved Please turn over

Downloaded from hlayiso.com Electrical Technology: Digital Electronics 15 DBE/2022 SC/NSC 5.3.2 FIGURE 5.3.2 below shows a circuit diagram of a two-digit binary input to four-digit decimal output decoder. Determine the output at W, X, Y and Z when input A is '02' and input B is '12'. A=0 B=1 W X Y Z FIGURE 5.3.2 (4) 5.4 FIGURE 5.4 below represents the logic symbol of a D-type flip-flop. D Q CLK Q FIGURE 5.4 5.4.1 Complete the logic circuit of this flip-flop using the information given on the ANSWER SHEET for QUESTION 5.4.1. (6) 5.4.2 Complete the truth table of this flip-flop in the table below on the ANSWER SHEET for QUESTION 5.4.2. INPUTS OUTPUTS CLK D Q Q 0 0 Latch 0 1 1 0 1 1 TABLE 5.4.2 (3) Copyright reserved Please turn over

Downloaded from hlayiso.com Electrical Technology: Digital Electronics 16 DBE/2022 SC/NSC 5.5 FIGURE 5.5 below represents the logic symbol of a full adder. Complete the logic circuit of the full adder using the information given on ANSWER SHEET 5.5. A Σ B F/A CO Ci FIGURE 5.5 (8) 5.6 Refer to FIGURE 5.6 below of a three-stage binary counter and answer the questions that follow. 1 A B C FF0 FF1 FF2 SET SET SET J Q J Q J Q K CLR Q K CLR Q K CLR Q Input clock pulses FIGURE 5.6 THREE-STAGE BINARY COUNTER 5.6.1 Complete the timing diagrams for this counter on the ANSWER SHEET for QUESTION 5.6.1. (8) 5.6.2 State whether the circuit in FIGURE 5.6 is synchronous or asynchronous. (1) 5.7 State TWO applications of the up/down counter. (2) 5.8 Complete the sketch of a 4-bit serial-in: serial-out shift register using the information given on the ANSWER SHEET for QUESTION 5.8. (7) [55] Copyright reserved Please turn over

Downloaded from hlayiso.com Electrical Technology: Digital Electronics 17 DBE/2022 SC/NSC QUESTION 6: MICROCONTROLLERS 6.1 Name TWO uses of a microcontroller in industrial control devices. (2) 6.2 Draw the sequential operating (scan) cycle of the CPU. (4) 6.3 Explain the difference between a microprocessor and a microcontroller with reference to the hardware of microcontrollers. (4) 6.4 Refer to registers within the CPU and answer the questions that follow. 6.4.1 Explain the function of a memory data register (MDR). (2) 6.4.2 Explain the function of a current instruction register (CIR). (3) 6.5 Refer to communication in a microcontroller and define the term hardware interface. (2) 6.6 Draw a block diagram of full duplex communication. (4) 6.7 Answer the following questions with reference to serial communication interface. 6.7.1 Write out the abbreviation UART in full. (1) 6.7.2 List THREE advantages of the UART. (3) 6.7.3 Explain the operation of the UART. (6) 6.8 Answer the questions that follow with reference to communication protocols. 6.8.1 Name THREE applications of the RS-485. (3) 6.8.2 State the line configuration of the RS-485. (1) 6.9 State the purpose of an analogue-to-digital-converter (ADC) with reference to the hardware of microcontrollers. (3) 6.10 Explain the relationship between algorithms and flowcharts with reference to the software of microcontrollers. (4) 6.11 Complete the flow chart of a monitoring system at a fuel station on the ANSWER SHEET for QUESTION 6.11. A fuel station has three tanks, each with a level-monitoring sensor. The sensors will be activated when the fuel level reaches the bottom of each tank. The alarm will sound if any of the sensors is activated. The system must include a reset function. NO time delay is needed. (8) [50] TOTAL: 200 Copyright reserved

Downloaded from hlayiso.com Electrical Technology: Digital Electronics DBE/2022 SC/NSC FORMULA SHEET SEMICONDUCTOR DEVICES VOUT  RF  RF Gain A V      OR AV  1 VIN  R IN  RIN  R  VOUT  VIN    F   R IN   R  VOUT  VIN  1  F   R IN  SWITCHING CIRCUITS  R R R  VOUT    V1 F  V2 F  ...VN F   R1 R2 RN  VOUT VOUT Gain A V   VIN V1  V2  ...VN  VOUT   (V1  V2  ...VN ) FLOW CHART SYMBOLS Process Decision Terminator Data Copyright reserved

Downloaded from hlayiso.com Electrical Technology: Digital Electronics DBE/2022 SC/NSC CENTRE NUMBER: EXAMINATION NUMBER: ANSWER SHEET QUESTION 3: SWITCHING CIRCUITS 3.3.5 Vin V Vref Input t Vsat Transfer mark to answer book Output MOD t FIGURE 3.3.5 (3) 3.4.6 +V Upper trigger voltage 0 Lower trigger voltage -V +Vsat 0 Transfer mark to answer book MOD -Vsat FIGURE 3.4.6 (4) Copyright reserved

Downloaded from hlayiso.com Electrical Technology: Digital Electronics DBE/2022 SC/NSC CENTRE NUMBER: EXAMINATION NUMBER: ANSWER SHEET 3.6.1 V Input t Vsupply Transfer mark to answer book Output t MOD FIGURE 3.6.1 (3) 3.6.2 V Input t Vsupply Transfer mark to answer book Output t MOD FIGURE 3.6.2 (3) Copyright reserved

Downloaded from hlayiso.com Electrical Technology: Digital Electronics DBE/2022 SC/NSC CENTRE NUMBER: EXAMINATION NUMBER: ANSWER SHEET QUESTION 4: SEMICONDUCTORS 4.2.3 V Trigger t input Capacitor voltage t Transfer mark to answer book Output voltage MOD t (4) FIGURE 4.2.3 Copyright reserved

Downloaded from hlayiso.com Electrical Technology: Digital Electronics DBE/2022 SC/NSC CENTRE NUMBER: EXAMINATION NUMBER: ANSWER SHEET QUESTION 5: DIGITAL AND SEQUENTIAL DEVICES 5.3.1 +5 V R1 R2 R3 S1 1 A0 S2 2 S3 3 A1 Transfer mark to answer book MOD FIGURE 5.3.1 (6) Copyright reserved

Downloaded from hlayiso.com Electrical Technology: Digital Electronics DBE/2022 SC/NSC CENTRE NUMBER: EXAMINATION NUMBER: ANSWER SHEET 5.4.1 D Q CLK Q Transfer mark to answer book MOD FIGURE 5.4.1 (6) Copyright reserved

Downloaded from hlayiso.com Electrical Technology: Digital Electronics DBE/2022 SC/NSC CENTRE NUMBER: EXAMINATION NUMBER: ANSWER SHEET 5.4.2 INPUTS OUTPUTS CLK D Q Q 0 0 Latch Transfer mark to answer book 0 1 1 0 1 1 MOD TABLE 5.4.2 (3) 5.5 Ci Σ A Co B Transfer mark to answer book MOD FIGURE 5.5 (8) Copyright reserved

Downloaded from hlayiso.com Electrical Technology: Digital Electronics DBE/2022 SC/NSC CENTRE NUMBER: EXAMINATION NUMBER: ANSWER SHEET 5.6.1 1 2 3 4 5 6 7 8 Clock pulses Output A Output B Output C Transfer mark to answer book MOD FIGURE 5.6.1 (8) Copyright reserved

Downloaded from hlayiso.com Electrical Technology: Digital Electronics DBE/2022 SC/NSC CENTRE NUMBER: EXAMINATION NUMBER: ANSWER SHEET 5.8 Serial D Q Data in FFA Clock CLK Q D Q FFB CLK Q D Q FFC CLK Q Serial D Q Data out FFD CLK Q Transfer mark to answer book MOD FIGURE 5.8 (7) Copyright reserved

Downloaded from hlayiso.com Electrical Technology: Digital Electronics DBE/2022 SC/NSC CENTRE NUMBER: EXAMINATION NUMBER: ANSWER SHEET QUESTION 6: MICROCONTROLLERS 6.11 Start Transfer mark to answer book MOD FIGUUR 6.11 (8) Copyright reserved