Exam (elaborations)
1.3.3-Input-devices
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Exam of 18 pages for the course IGCSE at IGCSE (1.3.3-Input-devices)
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QUESTION 1. 128 An alarm clock is controlled by a microprocessor. It uses the 24 hour clock. The hour is represented
by an 8-bit register, A, and the number of minutes is represented by another 8-bit register, B.
(a) Identify what time is represented by the following two 8-bit registers.
A B
128 64 32 16 8 4 2 1 128 64 32 16 8 4 2 1
0 0 0 1 0 0 1 0 : 0 0 1 1 0 1 0 1
Hours ............................................ Minutes .........................................
[2]
(b) An alarm has been set for 07:30. Two 8-bit registers, C and D, are used to represent the
hours and minutes of the alarm time.
Show how 07:30 would be represented by these two registers:
C D
:
Hours Minutes
[2]
(c) Describe how the microprocessor can determine when to sound the clock alarm.
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© UCLES 2015 0478/11/M/J/15
, 13
(d) The LCD (liquid crystal display) on the clock face is back-lit using blue LEDs (light emitting
diodes). The brightness of the clock face is determined by the level of light in the room. The
amount of light given out by the LEDs is controlled by a control circuit.
Describe how the sensor, microprocessor and LEDs are used to maintain the correct
brightness of the clock face.
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(e) Modern LCD monitors and televisions use LED back-lit technology.
Give two advantages of using this new technology compared to the older cold cathode
fluorescent lamp (CCFL) method.
1 ................................................................................................................................................
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2 ................................................................................................................................................
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[2]
© UCLES 2015 0478/11/M/J/15 [Turn over
, QUESTION 2. 10
7 (a) Street lighting is controlled automatically. A light sensor and a microprocessor are used to
decide when to switch each street light on or off.
Describe how the sensor, microprocessor and light interact to switch the street light on or off.
Include in your answer how the microprocessor stops the street lights being frequently
switched on and off due to brief changes in the light intensity.
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(b) Name three different sensors (other than light and pH) and describe an application for each
of these sensors.
A different application is needed for each sensor.
Sensor 1 ...................................................................................................................................
Application ................................................................................................................................
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Sensor 2 ...................................................................................................................................
Application ................................................................................................................................
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Sensor 3 ...................................................................................................................................
Application ................................................................................................................................
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[6]
© UCLES 2015 0478/12/M/J/15
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