The Pelican Crossing is a signalised crossing used on public highways and incorporates audio equipment to generate audio tones to assist visually impaired pedestrians to cross safely. At single carriageway crossing sites, a ‘single bleep’ audio signal is generated whereas at a ‘staggered crossing facility’ a ‘bleep and sweep’ audio signal is generated. Both types of audio signal are generated when the green man, safe to cross, is displayed.
In addition to the audio signal, when the pedestrian ‘push to cross’ button is pressed, digital electronic equipment generates the correct traffic lights sequence.
The normal traffic lights sequence will be displayed using appropriate coloured LEDs.
The fundamental frequency of the ‘single bleep’ tone can be between 2.0 kHz and 3.5 kHz, pulsed at 240 ± 10 pulses per minute with a mark space ratio of 1.5:1 ± 10%.
The audio signal will be fed into an external audio amplifier. Figure 1 shows the block diagram for the Pelican Crossing system
You are required to design, simulate and build the digital electronic circuits that make up the complete system except for the audio amplifier which will be provided to test the system.
The assignment is to be written up as a technical report that should include; your design procedure, circuit diagrams, simulation results, results, a discussion of the results and a conclusion. The report is to be written using a suitable text editor such as Microsoft Word and submitted on-line using Turnitin on Blackboard. The technical report is to be written in the third person, ie do not use ‘I’, ‘we’, ‘you’ etc. There will be marks for presentation of the report.
Guidelines for the structure of the report:
- Abstract: Summary of the work undertaken.
- Objectives: List a number of objectives or stages required to complete the work.
- List of equipment and components used: All the components and equipment used for practical work should be listed. Record make, model and serial number of equipment used.
- Circuit diagram: Neat and clear schematic diagrams with correct technical symbols, labels and component values.
- Principle of operation: A brief explanation of circuit operations with any necessary equations and expressions.
- Calculations: Clear step by step calculations if required.
- Measurements/results: All measurements such as logic levels/timing diagrams, waveforms etc should be recorded.
- Simulation results: The clear and readable printouts of schematic and simulation results with very brief introduction. Avoid screen dumps.
- Discussion: Brief discussion of the results. Provide any comparisons between; theoretical and practical results with theory.
- Conclusion: Brief conclusion of the work undertaken in the assignment.
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