A large household hardware chain requires a cost e elective water tank meter to be developed for
the home improvement market. The system should display the amount of Litres in the tank on
a 8bit LCD screen. Remembering that 1m3 = 1000L. The water tank dimensions with which
this system will work are shown below. It is assumed the shape is a perfect cylinder.
Height = 5m
Diameter= 3m
To measure the volume of the tank an ultrasonic sensor is placed at the top of the tank which
measures the distance between the sensor and the water below it. From its measurement the
height of the water and therefore the volume of water in the tank can be deduced.
The following table describes the series of ultrasonic sensors which are available for use in the
design. Assume that the sensor is placed at the top of the tank. Also Assume that water in
the tank never goes passed the minimum sensor range.
ebrotal ultrasonic sensors
Model Tu89 Tu89b Tu89c Tu89d Tu64a Tu64b Tu90b Tu90c
Price $25 $22 $24 $35 $45 $40 $90 $60
Range 5cm!1.25m 15cm!3.55m 25cm!4.2m 35cm!6m 50cm!11m 40cm!7.6m
Output 0 to 5V
Temperature -20 to 60C -20 to 75C
Install Vertical Top of the tank
Pressure 2bar 2.5Bar
A Z8encore series, F0830 or 64k, micro controller must be used. It is up to the designer to choose
a suitable part. Datasheets for the Z8encore F0830 and 64k series micro-controllers are pro-
vided on LMS. Note that the great thing about the Z8encore series of processors is that they all
operate identically. The only di erence is that the smaller versions essentially only have fewer
pins and less peripherals, but are programmed in exactly the same way. It may be helpful to
look at the Pin Con guration section to determine your choice.
The LCD with which the water volume will be displayed is the same one used by the calculator
board used in the labs. Detail of which can be found on LMS.
2 Questions (Design)
1. What is the most cost elective ultra-sonic sensor suitable for the tank dimensions? [2]
Ultra-sonic Sensor:
2. What hardware resources do we need in the Z8 controller to achieve the functionality [2]
required for this design? In your answer list the internal resources needed (ports, on-board
peripherals etc.).
3. Mathematical implementation
(a) What is minimum di erence in water height that the system can accurately sense. In [2]
other words what is the resolution of the measured water height. Consider the chosen
sensor and accuracy of the ADC. Show working.
(b) Derive a mathematical function which uses the ADC value, which should be refereed [5]
to as `ADC’, to calculate the volume of the tank in litres. Show all working in the
space below including a plot showing ADC value vs height. Ensure that your formula
is given in its simplest form.
Please provide your answer to three decimal places for all variables.
Volume = L
(c) What problems may arise if the sensor returns a reading outside the maximum height [3]
of the tank? Why does this occur? What could you do in the code to stop these
errors from being displayed?
(d) If the embedded system was to use xed point arithmetic, using your mathematical [3]
function what is the accuracy of the system in Litres?
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