Hardware Systems & Design

| January 30, 2016

Hardware Systems & Design
Project description
ELEE1062 Hardware Systems & Design: Microcontroller Project
Introduction:
Microcontroller based hardware systems can be used to process real world information from various sensors and to produce an output to show the result. Sensors can
respond to various physical parameters such as mass, temperature, velocity etc. or the occurrence of a particular event. An example is an ultrasonic rangefinder, which
is a device that sends out ultrasonic pulses and detects when the pulses reflect back from a physical object. The timing of the reflected pulse can be used to
determine distance.
For this project, you will use an ultrasonic rangefinder and the DE0 development board running a NIOS II processor to construct a distance measuring device and present
the result on a seven segment LED display.
Project:
Part 1: Develop and implement C code for the NIOS processor, running on the Altera DE0 development board, that uses an SRF05 ultrasonic rangefinder to create a
distance measurement device. Use a single seven segment display on the DE0 board to display the distance result, in centimetres, up to a limit of 9 centimetres.
Part 2: Make use of the other seven segment displays of the DE0 board to display the result in millimetres, up to the maximum range of the sensor.
Part 3: Make use of the pushbuttons and/or switches to store the greatest and least distance values. Include a reset mechanism.
Deliverables:
1. Formal report including: a) Title page b) Contents page c) Introduction d) Design methodology, including a full account of the development process e) Testing and
results f) Discussion g) Conclusion h) C code (with comments) in the appendix
The report must be submitted electronically via an upload link that will be available in Moodle. Length: 2000 words (+/- 10%).
2. Hardware demonstration
You will be given a time slot to demonstrate and explain your hardware system.
Your grade will be composed of:
a) Technical quality of your work as documented in the report and seen in the demonstration. This includes the technical quality of the development and testing as well
as the final result. (60%) b) Structure and presentation of the report (40%).
SRF05 – Ultra-Sonic Ranger
Technical Specification
Introduction
The SRF05 is an evolutionary step from the SRF04, and has been designed to increase flexibility, increase range, and to reduce costs still further. As such, the SRF05
is fully compatible with the SRF04. Range is increased from 3 meters to 4 meters. A new operating mode (tying the mode pin to ground) allows the SRF05 to use a single
pin for both trigger and echo, thereby saving valuable pins on your controller. When the mode pin is left unconnected, the SRF05 operates with separate trigger and
echo pins, like the SRF04. The SRF05 includes a small delay before the echo pulse to give slower controllers such as the Basic Stamp and Picaxe time to execute their
pulse in commands.
Mode 1 – SRF04 compatible – Separate Trigger and Echo
This mode uses separate trigger and echo pins, and is the simplest mode to use. All code examples for the SRF04 will work for the SRF05 in this mode. To use this mode,
just leave the mode pin unconnected – the SRF05 has an internal pull up resistor on this pin.
Mode 2 – Single pin for both Trigger and Echo
This mode uses a single pin for both Trigger and Echo signals, and is designed to save valuable pins on embedded controllers. To use this mode, connect the mode pin to
the 0v Ground pin. The echo signal will appear on the same pin as the trigger signal. The SRF05 will not raise the echo line until 700uS after the end of the trigger
signal. You have that long to turn the trigger pin around and make it an input and to have your pulse measuring code ready. The PULSIN command found on many popular
controllers does this automatically.
To use mode 2 with the Basic Stamp BS2, you simply use PULSOUT and PULSIN on the same pin, like this:
SRF05 PIN 15 ‘ use any pin for both trigger and echo
Range VAR Word ‘ define the 16 bit range variable
SRF05 = 0 ‘ start with pin low
PULSOUT SRF05, 5 ‘ issue 10uS trigger pulse (5 x 2uS)
PULSIN SRF05, 1, Range ‘ measure echo time
Range = Range/29 ‘ convert to cm (divide by 74 for inches)
Calculating the Distance
The SRF05 Timing diagrams are shown above for each mode. You only need to supply a short 10uS pulse to the trigger input to start the ranging. The SRF05 will send out
an 8 cycle burst of ultrasound at 40khz and raise its echo line high (or trigger line in mode 2). It then listens for an echo, and as soon as it detects one it lowers
the echo line again. The echo line is therefore a pulse whose width is proportional to the distance to the object. By timing the pulse it is possible to calculate the
range in inches/centimeters or anything else. If nothing is detected then the SRF05 will lower its echo line anyway after about 30mS.
The SRF04 provides an echo pulse proportional to distance. If the width of the pulse is measured in uS, then dividing by 58 will give you the distance in cm, or
dividing by 148 will give the distance in inches. uS/58=cm or uS/148=inches.
The SRF05 can be triggered as fast as every 50mS, or 20 times each second. You should wait 50ms before the next trigger, even if the SRF05 detects a close object and
the echo pulse is shorter. This is to ensure the ultrasonic “beep” has faded away and will not cause a false echo on the next ranging.
The other set of 5 pins
The 5 pins marked “programming pins” are used once only during manufacture to program the Flash memory on the PIC16F630 chip. The PIC16F630’s programming pins are also
used for other functions on the SRF05, so make sure you don’t connect anything to these pins, or you will disrupt the modules operation.
Changing beam pattern and beam width
You can’t! This is a question which crops up regularly, however there is no easy way to reduce or change the beam width that I’m aware of. The beam pattern of the
SRF05 is conical with the width of the beam being a function of the surface area of the transducers and is fixed. The beam pattern of the transducers used on the
SRF05, taken from the manufacturers data sheet, is shown below.
There is more information in the sonar faq.
Dimensions

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