You're looking for a guide on electronic projects for beginners by AK Maini, specifically the 21st project in a PDF format. I'll provide you with some general information and possible resources.
Practical Troubleshooting: Testing guidelines and suggestions for alternative components if specific parts are hard to find. User Feedback & Critical Perspectives electronic projects for beginners by akmaini pdf 21
Unlike many modern "plug-and-play" project books, Maini includes "Lead/Pin identification" and testing guidelines You're looking for a guide on electronic projects
Water Tank Overflow / Rain Alarm: Uses the conductivity of water to trigger a buzzer—a classic "first project". electronic projects for beginners by akmaini pdf 21