DIY Electronics for Signal Detection in the Presence of Noise

For a classroom SONAR demo, a Do It Yourself (DIY) Probability Density Function (PDF) circuit is used to distinguish between two PDF distributions; one which is noise, the other a signal embedded within the noise. The output of the microphone is input into an analog energy detector. The energy distribution acquired by squaring the input and averaging over a time window (via a 1kHz LPF) is then (a) binned by a voltage window comparator, (b) chopped (multiplied) by a fast (112 microsecond) clock, and (c) coupled to a digital counter (6 digit display). Comparing the distributions (counts per bin) leads to a detection index (DI) whose value establishes the criteria for resolving the two PDFs. A Receiver Operating Characteristic (ROC) curve is generated for corresponding data probabilities: (a) false alarms (b) signal detection.