Section C — Design and application (30 marks) 10. (10 marks) Design a compact, battery-powered LED flasher (approx 1 Hz) based on a circuit concept from “302 Circuits”. Requirements: runs from a single 3.7 V Li-ion cell, drives a white LED (forward voltage 3.0 V) at 20 mA with suitable current-limited pulsed drive, uses minimal parts, includes a schematic and component list with values, and explains how you ensure safe battery discharge and LED current limiting. (Include a short PCB/component placement note.) 11. (8 marks) Modify a published tone-generator circuit (astable op-amp or NE555) to produce an adjustable square-to-sine-like audio output from 400 Hz to 4 kHz with amplitude suitable for feeding into a small power amp (line-level). Provide a block diagram, component choices, and explain how tone and waveform shaping are achieved. 12. (6 marks) Propose an EMI mitigation plan for a switching power-supply circuit found in the collection: list five practical measures (e.g., snubbers, layout changes, filtering) and briefly explain the purpose of each. 13. (6 marks) Select one project-type from the book (e.g., FM transmitter, logic trainer, measurement accessory). Describe enhancements to improve reliability and usability: three hardware changes and two documentation/user-interface improvements.