cameroon gce intermediate level 2025 electronic systems 2
cameroon gce intermediate level 2025 electronic systems 2
THEME: ELECTRONIC CONTROL OF A PISTOL
The device uses electronics to eject a bullet. Generally, when the trigger of the pistol is activated, a pulse is generated to trigger a monostable multivibrator and to activate a buzzer. The output of the monostable serves as the control input of the first astable multivibrator. The output of the first astable serves as the control input of the second astable multivibrator. The output of the second astable multivibrator is used to drive a circuit made up of two transistors. The collector of the two transistor circuit is found an infrared diode. This diode emits infrared rays that is receives by a receiver circuit. The signal receives by the receiver is processed and is counted when the bullet hits the required target. A loudspeaker produces sound when the required target is hit. The user observed that the device no longer operates as required. He then seeks your expertise to eliminate the problem. This equipment whose circuit diagram is represented in figure 1 on page 7 contains amongst other electronic functions those of power supply, timing circuit, counting, interfacing and display circuits. In your capacity as a qualified electronic technician, you have been charged to carry out repairs on this equipment. Extract of some technical documents, represented on page 6, have equally been placed at your disposal to facilitate your task. Carefully exploit these documents and answer the questions in the following two sections.1
1. Power supply2
Figure 2 shows the circuit diagram of the power supply used in this system.3
1.14 Draw the block diagram of the linear regulated power supply. (3 marks)
1.2 Name three types of linear regulated power supply. (3 marks)
1.3 Calculate the transformation ratio of the transformer. (2 marks)
1.4 What is the role of the transformer in this linear regulated power supply? (1 mark)
1.5 Calculate the peak inverse voltage across the diode labelled D1. (1 mark)
1.6 Calculate the maximum voltage at the input to the integrated regulated power supply. (1 mark)
1.7 Deduce from the following the voltage rating of the capacitor labelled C1: 10V, 16V and 25V. (1 mark)
1.8 Sketch the waveform obtained at the input of the integrated regulator. (2 marks)
1.9 If the diode D2 is open, sketch the waveform obtained at the input of the integrated regulated power supply. (2 marks)
1.10 Give the role of each of the following capacitors:
- C1 (1 mark)
- C2 (1 mark)
- C3 (1 mark)1.11 If the forward current of the LED is 30mA and the threshold voltage across the LED is 2V, calculate the resistance of the resistor R1 and standardize its value from the E12 series. (3 marks)
1.12 It was observed that the supply from ENEO is on but the red LED is OFF. Use flow chart to troubleshoot and repair the system. (3 marks)
2. The emitter circuit
It is made up of the bullet generation impulse circuit, the time base circuits, and the sound generation circuit.
2.1 Bullet impulse generation
The impulse is generated when the trigger is activated.
2.1.1 Identify the circuit block made up of NAND I and II of IC1, C4 and R3. (1 mark)
2.1.2 What is the role of C3 to this circuit block? (1 mark)
2.1.3 What is the logic state at pin 6 of IC1 at steady state? (1 mark)
2.1.4 If C4 = 1μF and R4 = 100KΩ, calculate the pulse width of the signal produced at pin 4 of IC1. (3 marks)
2.1.5 When the output of the bullet impulse generation circuit is high, the buzzer starts producing sound.
2.1.5.1 Give the name of the circuit implemented with IC3. (1 mark)
2.1.5.2 If R11 = 10KΩ and C11 = 15nF, calculate the period of the signal produced at pin 3 of IC3. (1 mark)
2.1.5.3 Deduce the frequency of the signal produced at pin 3. (1 mark)
2.2 Time base circuits
The output of the bullet impulse generation circuit serves as the control input to the first time base made up of NAND I and II of IC2, R5, R6, C6 and D1.
2.2.1 What is the role of the diode D1? (1 mark)
2.2.2 If R5 = 470KΩ, R6 = 47KΩ and C6 = 22nF, calculate the period of the signal obtained at pin 4 of IC2. (2 marks)
2.2.3 Deduce the frequency of the signal obtained at pin 4 of IC2. (1 mark)
2.2.4 The output of the first time base serves as the control input to the second time base which is made up of NAND III and IV of IC2, R7 and C8.
2.2.4.1 Copy and complete the wave form below. (6 marks)
