Electrical Technology Nov 2018 (Digitals) Eng hlayiso.com

Downloaded from hlayiso.com GRAAD 12 NATIONAL SENIOR CERTIFICATE GRADE 12 ELECTRICAL TECHNOLOGY: DIGITAL NOVEMBER 2018 MARKS: 200 TIME: 3 hours This question paper consists of 15 pages, a 1-page formula sheet and 10 answer sheets. Copyright reserved Please turn over

Downloaded from hlayiso.com Electrical Technology: Digital 2 DBE/November 2018 NSC INSTRUCTIONS AND INFORMATION 1. This question paper consists of FIVE questions. 2. Answer ALL the questions. 3. Answer the following questions on the attached ANSWER SHEETS: QUESTION 2.3.2 QUESTIONS 2.4.1, 2.5.2, 2.6.3, 2.7.4, 2.8.1, 2.8.2 and 2.9.1 QUESTION 3.1.3 QUESTIONS 4.3 and 4.5.2 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. Show the units for ALL answers of calculations. 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 3 DBE/November 2018 NSC QUESTION 1: OCCUPATIONAL HEALTH AND SAFETY (GENERIC) 1.1 Define the term major incident with reference to the Occupational Health and Safety Act, 1993 (Act 85 of 1993). (2) 1.2 State TWO general duties of manufacturers with regard to a product that will be used at the workplace. (2) 1.3 Explain why horseplay is an unsafe act in the workshop. (2) 1.4 State TWO procedures that you have to follow to protect yourself when you help a person who is being shocked by electricity. (2) 1.5 Define the term qualitative risk analysis. (2) [10] QUESTION 2: SWITCHING CIRCUITS (SPECIFIC) 2.1 Explain the purpose of an astable multivibrator. (2) 2.2 Refer to FIGURE 2.2 below and answer the questions that follow. C1 +V Trigger input Output R2 -V 1 R1 Trigger 2 t pulse R3 0V FIGURE 2.2: MULTIVIBRATOR 2.2.1 Identify the multivibrator in FIGURE 2.2. (1) 2.2.2 Name the type of feedback provided by R 2. (1) 2.2.3 Describe the change in the output signal with reference to input trigger pulses 1 and 2. (3) Copyright reserved Please turn over

Downloaded from hlayiso.com Electrical Technology: Digital 4 DBE/November 2018 NSC 2.3 FIGURE 2.3 below shows the 555 IC astable multivibrator and the voltage graph of capacitor C 1 . Answer the questions that follow. +VCC R1 47 kΩ 8 4 7 R2 555 47 kΩ 3 OUT VC1 2 ⅔ VCC 6 1 5 C1 C2 ⅓ VCC 10 µF 10 nF t1 t2 t FIGURE 2.3: 555 IC ASTABLE MULTIVIBRATOR 2.3.1 Name ONE application of an astable multivibrator. (1) 2.3.2 Draw the output signal with reference to signal V C1 on ANSWER SHEET 2.3.2. (2) 2.3.3 Describe how an increase in the value of R 1 will affect the output signal. (3) Copyright reserved Please turn over

Downloaded from hlayiso.com Electrical Technology: Digital 5 DBE/November 2018 NSC 2.4 FIGURE 2.4 below shows input trigger pulses A and B to a 555 monostable multivibrator. Answer the questions that follow. A B +VS Trigger pulse 0V t ⅔ VS Capacitor charging 0V t +VS Output 0V t FIGURE 2.4: MONOSTABLE MULTIVIBRATOR TRIGGER PULSES 2.4.1 Draw the output signal on ANSWER SHEET 2.4.1. (4) 2.4.2 Describe the condition that occurred at trigger pulse B. (2) 2.4.3 Explain why the condition that occurs at trigger pulse B does NOT affect the capacitor charging. (3) Copyright reserved Please turn over

Downloaded from hlayiso.com Electrical Technology: Digital 6 DBE/November 2018 NSC 2.5 Refer to FIGURE 2.5 below and answer the questions that follow. +5 V VIN VOUT RF -5 V 8 kΩ R1 2 kΩ 0V FIGURE 2.5: INVERTING SCHMITT TRIGGER 2.5.1 Name TWO transducers that can be used as input devices to the Schmitt trigger. (2) 2.5.2 Draw the output signal on ANSWER SHEET 2.5.2 if the input signal in FIGURE 2.5.2 below is applied to the circuit. Upper +1 V trigger level Lower -1 V trigger level FIGURE 2.5.2: INPUT SIGNAL (4) 2.5.3 Describe how a decrease in the value of R 1 will affect the trigger voltage level of the Schmitt trigger. (3) Copyright reserved Please turn over

Downloaded from hlayiso.com Electrical Technology: Digital 7 DBE/November 2018 NSC 2.6 FIGURE 2.6 shows the 741 op amp as a comparator. Answer the questions that follow. +V R1 VIN +V VREF VIN - VOUT 0V + RREF -V 0V 0V FIGURE 2.6: COMPARATOR 2.6.1 State the purpose of the comparator. (1) 2.6.2 Briefly explain how the comparator achieves its function. (3) 2.6.3 Draw the output signal on ANSWER SHEET 2.6.3, with reference to the input signal in FIGURE 2.6. (3) 2.7 Refer to FIGURE 2.7 below and answer the questions that follow. R1 10 kΩ RF 100 kΩ 100 mV R2 30 kΩ +12 V 150 mV - R3 5 kΩ + 50 mV VOUT -12 V 0V FIGURE 2.7: INVERTING SUMMING AMPLIFIER 2.7.1 Calculate the output voltage. (3) 2.7.2 Explain how this circuit can be modified to control the input voltage of each signal independently. (2) 2.7.3 Describe how this circuit can be modified to prevent DC from being fed back to the input voltage sources. (2) 2.7.4 Draw the output signal on ANSWER SHEET 2.7.4. (2) Copyright reserved Please turn over

Downloaded from hlayiso.com Electrical Technology: Digital 8 DBE/November 2018 NSC 2.8 FIGURE 2.8 below shows an op amp as a differentiator. Draw the output signals on ANSWER SHEET 2.8, when the signals shown in QUESTIONS 2.8.1 and 2.8.2, are applied to the input of the circuit. IF RF C +V - IIN VOUT + -V R 0V FIGURE 2.8: OP AMP AS DIFFERENTIATOR 2.8.1 Sine wave VIN 0V t (3) 2.8.2 Triangular wave VIN 0V t (3) Copyright reserved Please turn over

Downloaded from hlayiso.com Electrical Technology: Digital 9 DBE/November 2018 NSC 2.9 Refer to FIGURE 2.9 below and answer the questions that follow. IF CF RIN +V VIN - IIN VOUT + -V 0V FIGURE 2.9: OP AMP AS INTEGRATOR 2.9.1 Draw the output signal on ANSWER SHEET 2.9.1, when the input signal in FIGURE 2.9.1 below is applied. VIN 0V t FIGURE 2.9.1: INPUT SIGNAL (3) 2.9.2 Describe what will happen to the output signal if the RC time constant is short. (4) [60] QUESTION 3: SEMICONDUCTOR DEVICES (SPECIFIC) 3.1 FIGURE 3.1 below shows the 741 op amp. Answer the questions that follow. FIGURE 3.1: 741 OP AMP 3.1.1 Label pin 3. (1) 3.1.2 Name the type of package in which the integrated circuit (IC) above is constructed. (1) Copyright reserved Please turn over

Downloaded from hlayiso.com Electrical Technology: Digital 10 DBE/November 2018 NSC 3.1.3 Draw the output signal on ANSWER SHEET 3.1.3 if the signals in FIGURE 3.1.3 below are applied to the inputs of an op amp. +V 0V +V -V output +V 0V -V -V FIGURE 3.1.3: SIGNALS (2) 3.2 State the typical operating voltages of a 741 op amp. (2) 3.3 State TWO characteristics of an ideal op amp. (2) 3.4 Explain the difference between open-loop gain and closed-loop gain with reference to op amps. (2) 3.5 Calculate the output voltage of the op amp in FIGURE 3.5 below. +V VIN = 5 mV VOUT RF -V 220 kΩ RIN 440 Ω 0V FIGURE 3.5: OP AMP Given: V IN = 5 mV R IN = 440 Ω RF = 220 kΩ (3) Copyright reserved Please turn over

Downloaded from hlayiso.com Electrical Technology: Digital 11 DBE/November 2018 NSC 3.6 FIGURE 3.6 below shows the 555 IC. Answer the questions that follow. 0V 1 8 +Vcc Trigger 2 7 Discharge 555 IC Output 3 6 Threshold Reset 4 5 Control Control voltage Voltage FIGURE 3.6: 555 IC 3.6.1 Explain how the trigger input pin on a 555 IC achieves its function. (3) 3.6.2 Refer to FIGURE 3.6.2 below and explain the operation of the 555 timer when connected in monostable mode. +VCC Trigger input R1 R2 ⅓ VCC ⅔ VCC t 8 4 7 Capacitor Capacitor 555 voltage 6 monostable Voltage 3 OUT VC1 2 t 1 5 1 Tr output Output C1 C2 0 t1 t FIGURE 3.6.2: MONOSTABLE MULTIVIBRATOR (4) [20] Copyright reserved Please turn over

Downloaded from hlayiso.com Electrical Technology: Digital 12 DBE/November 2018 NSC QUESTION 4: DIGITAL AND SEQUENTIAL DEVICES (SPECIFIC) 4.1 Briefly explain how a liquid crystal display (LCD) controls the passing of light through it. (3) 4.2 Refer to an LED seven-segment display and illustrate the difference between a sinking output and a sourcing output using TWO simple diagrams. (4) 4.3 Study FIGURE 4.3 below of a decimal-to-binary encoder. Use the table on ANSWER SHEET 4.3 to complete the truth table. +5V +5 V R9 R8 R7 R6 R5 R4 R3 R2 R1 A≥ A0 B≥ A1 C≥ A2 D≥ A3 9 8 7 6 5 4 3 2 1 0V FIGURE 4.3: DECIMAL-TO-BINARY ENCODER (10) 4.4 Draw the block diagram of a four-bit parallel adder that will be able to add the following two numbers: A 3A 2A 1A 0 + B 3B 2B 1B 0 (7) Copyright reserved Please turn over

Downloaded from hlayiso.com Electrical Technology: Digital 13 DBE/November 2018 NSC 4.5 FIGURE 4.5 below represents the logic symbol of a J-K flip-flop. CLOCK CLK FIGURE 4.5: LOGIC SYMBOL OF J-K FLIP-FLOP 4.5.1 Draw the logic circuit of this flip-flop using AND gates and NOR gates. (7) 4.5.2 Complete the truth table of the flip-flop below on ANSWER SHEET 4.5.2. TABLE 4.5.2: TRUTH TABLE INPUTS OUTPUTS CLOCK J K Q � 𝐐 0 0 0 1 1 0 1 1 (4) 4.6 Describe the difference between a synchronous counter and an asynchronous counter. (2) 4.7 FIGURE 4.7 below shows a three-stage synchronous self-stopping up-counter. Explain the operation of this counter. A B C LSB MSB 0 0 & 0 0 0 0 & SET SET SET J Q J Q J Q CLR K CLR Q K CLR Q K Q FF0 FF1 FF2 CLOCK CLK FIGURE 4.7: THREE-STAGE SYNCHRONOUS SELF-STOPPING UP-COUNTER (8) 4.8 Draw a neatly labelled sketch of a 4-bit serial-in parallel-out shift register using D-type flip-flops. Show ALL inputs and outputs. (10) [55] Copyright reserved Please turn over

Downloaded from hlayiso.com Electrical Technology: Digital 14 DBE/November 2018 NSC QUESTION 5: MICROCONTROLLERS (SPECIFIC) 5.1 State TWO uses of a microcontroller in commercial devices. (2) 5.2 State TWO advantages of a microcontroller. (2) 5.3 Explain the basic process that a microcontroller follows to fulfil its function. (4) 5.4 Refer to the block diagram of communication in a microcontroller in FIGURE 5.4 below. Answer the questions that follow. Memory A C RAM/ROM RAM/ROM X System Bus Y Data Bus FIGURE 5.4: COMMUNICATION IN A MICROCONTROLLER 5.4.1 Label the following blocks in FIGURE 5.4: (a) A (1) (b) C (1) 5.4.2 Identify the following bus connections: (a) X (1) (b) Y (1) 5.5 Define the following elements in a microcontroller: 5.5.1 Protocol (1) 5.5.2 Communication protocol (2) 5.5.3 Hardware interface (2) Copyright reserved Please turn over

Downloaded from hlayiso.com Electrical Technology: Digital 15 DBE/November 2018 NSC 5.6 Refer to registers within the CPU and answer the questions that follow. 5.6.1 Briefly define a register. (2) 5.6.2 Describe the function of a register. (2) 5.6.3 Name TWO types of registers that are used in the CPU of a microcontroller. (2) 5.6.4 Explain the function of the memory data register. (2) 5.7 Discuss the read-only memory (ROM) with reference to the CPU of a microcontroller. (4) 5.8 Draw the serial communication block diagram for: 5.8.1 Synchronous communication (4) 5.8.2 Asynchronous communication (4) 5.9 Name THREE types of communication peripherals. (3) 5.10 Give the reason why the RS-485 communication protocol is used in industrial applications. (2) 5.11 Identify the following flow diagram symbols: 5.11.1 (1) 5.11.2 (1) 5.11.3 (1) 5.12 Design a flow diagram of a home security system that has THREE sensors in different parts of the house. If any one of the sensors is activated, the alarm will be activated. The alarm must include a reset function. No timing function is required. (10) [55] TOTAL: 200 Copyright reserved

Downloaded from hlayiso.com Electrical Technology: Digital DBE/November 2018 NSC FORMULA SHEET SEMICONDUCTOR DEVICES VOUT  RF  Gain A V = = −   VIN  R IN   R  VOUT = VIN ×  − F   R IN   R  VOUT = VIN × 1 + F   R IN  SWITCHING CIRCUITS VOUT = − ( V1 + V2 + V3 + ....VN )  R   R   R  VOUT = VIN 1×  − F  + VIN 2 ×  − F  + ... .VINN ×  − F   R1   R2   RN  Copyright reserved

Downloaded from hlayiso.com Electrical Technology: Digital DBE/November 2018 NSC EXAMINATION NUMBER: CENTRE NUMBER: ANSWER SHEET 2.3.2 Input +V CC -V CC t VOUT +V 0V t1 t2 t FIGURE 2.3.2 (2) Copyright reserved

Downloaded from hlayiso.com Electrical Technology: Digital DBE/November 2018 NSC EXAMINATION NUMBER: CENTRE NUMBER: ANSWER SHEET 2.4.1 A B +VS Trigger pulse 0V t ⅔ VS Capacitor charging 0V t +VS Output 0V t FIGURE 2.4.1 (4) Copyright reserved

Downloaded from hlayiso.com Electrical Technology: Digital DBE/November 2018 NSC EXAMINATION NUMBER: CENTRE NUMBER: ANSWER SHEET 2.5.2 +1 V Upper trigger level Lower -1 V trigger level +V Output -V FIGURE 2.5.2 (3) Copyright reserved

Downloaded from hlayiso.com Electrical Technology: Digital DBE/November 2018 NSC EXAMINATION NUMBER: CENTRE NUMBER: ANSWER SHEET 2.6.3 VIN VREF 0V +VSAT -VSAT FIGURE 2.6.3 (3) Copyright reserved

Downloaded from hlayiso.com Electrical Technology: Digital DBE/November 2018 NSC EXAMINATION NUMBER: CENTRE NUMBER: ANSWER SHEET 2.7.4 100 mV t 150 mV t 50 mV t VOUT = V ______ out t 90° 180° 270° 360° FIGURE 2.7.4 (2) Copyright reserved

Downloaded from hlayiso.com Electrical Technology: Digital DBE/November 2018 NSC EXAMINATION NUMBER: CENTRE NUMBER: ANSWER SHEET 2.8 VIN 0V t VOUT 0V t 90° 180° 270° 360° FIGURE 2.8.1 (3) VIN 0V t VOUT 0V 90° 180° 270° 360° t FIGURE 2.8.2 (3) Copyright reserved

Downloaded from hlayiso.com Electrical Technology: Digital DBE/November 2018 NSC EXAMINATION NUMBER: CENTRE NUMBER: ANSWER SHEET 2.9.1 VIN 0V t 0V t -V FIGURE 2.9.1 (3) Copyright reserved

Downloaded from hlayiso.com Electrical Technology: Digital DBE/November 2018 NSC EXAMINATION NUMBER: CENTRE NUMBER: ANSWER SHEET 3.1.3 +V 0V Input 1 -V +V 0V Input 2 -V +V 0V output 90° 180° 270° 360° -V FIGURE 3.1.3 (2) Copyright reserved

Downloaded from hlayiso.com Electrical Technology: Digital DBE/November 2018 NSC EXAMINATION NUMBER: CENTRE NUMBER: ANSWER SHEET 4.3 INPUTS OUTPUTS 0 1 2 3 4 5 6 7 8 9 A3 A2 A1 A0 1 1 1 1 1 1 1 1 1 1 1 0 1 1 1 1 1 1 1 1 1 1 0 1 1 1 1 1 1 1 1 1 1 0 1 1 1 1 1 1 1 1 1 1 0 1 1 1 1 1 1 1 1 1 1 0 1 1 1 1 1 1 1 1 1 1 0 1 1 1 1 1 1 1 1 1 1 0 1 1 1 1 1 1 1 1 1 1 0 1 1 1 1 1 1 1 1 1 1 0 TABLE 4.3 (10) Copyright reserved

Downloaded from hlayiso.com Electrical Technology: Digital DBE/November 2018 NSC EXAMINATION NUMBER: CENTRE NUMBER: ANSWER SHEET 4.5.2 INPUTS OUTPUTS CLOCK J K Q � 𝐐 0 0 0 1 1 0 1 1 TABLE 4.5.2 (4) Copyright reserved