The method by which electrical signals convey information has been described.

Systems components have been selected and interfaced to enable a chosen system to perform a desired operation.

1. a) Draw an amplitude modulated waveform and describe which part of it contains the information to be conveyed.

b) List 2 advantages and 2 disadvantages in the amplitude modulated system.

2. a) Draw a frequency modulated waveform and describe which part of it contains the information to be conveyed.

b) List 2 advantages and 2 disadvantages of a frequency modulated system.

3. a) Draw a digital signal waveform and describe where the information is contained.

 b) List 2 advantages and 2 disadvantages of a digital system.

4. A domestic gas central heating system consists of the boiler, a programmer, a pump and a boiler thermostat.

 a) Draw a single block diagram to represent the system.

b) Draw a block diagram to represent the system. Include only one radiator for simplicity.

5 A strain gauge gives an output of 25 mV for a strain input of 1.8 mm/m. The transducer output is fed into a voltage amplifier with a gain of 80 and then into a moving coil voltmeter with a deflection of 20 °/V.

 a) Draw the block diagram of the system.

 b) What are the overall units of sensitivity?

c) Calculate the overall sensitivity.

d) What will be the deflection of the pointer on the voltmeter for a change in strain of 0.75 mm/m.

6. A closed loop speed control system for a dc motor is illustrated below. The electrical energy input to the motor is controlled by a low power electrical signal (Vi).

An error-actuated pre-amplifier feeds a drive amplifier, which in turn drives a dc motor. The motor speed is sensed by a speed transducer (tachogenerator) which sends a voltage signal to an error detector.

 a) Describe the purpose and operation of the Error Detector.

b) Calculate the input voltage that is required in order to maintain a motor speed of 1500 rpm for a given value of load.

c) Calculate the instantaneous change in error voltage if the load increases, causing the speed to fall instantaneously to 1200 rpm.

7. a) Describe and give diagrams of the load waveform, as to how the load energy is controlled by the control input variable in the circuit below.

 b) What might this type of energy control be used for?
 
The processing program, contained in the micro-controller, continually reads data from each of the sensors and stores this data in its memory, for later access. It also displays any data on 7-segment LED displays, on request.

8. For the system shown above:

a) Select and specify a suitable sensor or transducer for input number 1, you should provide a data sheet as an appendix.

b) Select and specify a suitable sensor or transducer for input number 2, you should provide a data sheet as an appendix.

c) Select and specify a suitable sensor or transducer for input number 3, you should provide a data sheet as an appendix.

9. a) Describe the function served by the multiplexer and demultiplexer.

b) Describe the function served by the hand shaking lines between the ADC and the micro-controller.

c) State the type, or types, of input signal conditioning required at each of the sensor outputs.

10. a) State the type, or types, of output signal conditioning required at each of the 7-segment display inputs.

b) Given that the ADC is 8-bit, and has an input analogue range of 0 to 3 volts, calculate the required gain of each sensor output amplifier used so as to maximise the accuracy of the ADC.

c) Calculate the 8-bit code at the ADC output that corresponds to an analogue input of 2.55 volts.

d) Determine the 8-bit code connected to a 7-segment LED display when it displays the value 5. Assuming the most significant bit is unused.