Back in May 1995, Bob Pease wrote an article about the “hassler” circuit used by analog great Bob Widlar. The circuit sensed loud voices and would emit a near-ultrasonic squeal to dissuade further yelling or boisterous behavior. Widlar designed the circuit to quiet anyone yelling in his office. It also discouraged typing from a nearby secretary.
The actual circuit Widlar used is lost to history, but Pease postulated his own circuit. Several co-workers agreed that it was close in function to the Widlar circuit. The article is not online, but I found an old bootleg .pdf copy. The schematic was in the inimitable Pease hand-drawn style (Fig. 1). The heart of the circuit is a 22-kHz ultrasonic oscillator with a voltage-controlled frequency. When it senses loud audio at the input, the frequency slows down and drops into the range of hearing, making a nice annoying squealing sound.
1. Bob Pease designed this “hassler” circuit in 1995. It makes a squealing noise if someone talks too loudly.
As a consultant, I became a stickler for clear readable schematics, so I re-drew Pease’s circuit in my old Cadence OrCAD 9.2 (Fig. 2). I made sure the schematic flowed from left to right and top to bottom. Rather than wrapping it into a U-shape like Pease, I broke mine into two sections with an off-sheet port to connect the two halves. It fits on an A-sized sheet in portrait mode.