The idea behind this snore alarm, is just to rouse the snorer, not the entire household. To wake the sleeper, vibration is used, not an audible alert. The vibration is provided by a small motor housed in a small 35mm film case, which can be placed under the sleepers mattress or pillow. This circuit has a level control and peak display indicator, a variable trigger threshold and trigger indication.
Sound is received by the microphone and amplified with IC1. An electret mic insert (ecm) was used in my prototype, but a dynamic mic insert of impedance 200 to 1k may also be used. If a dynamic mic is used, omit R1. IC1 functions as an active filter and reduces high frequency gain. At low frequencies gain is 47 times, starting to fall off above 1kHz. VR1 is the level control for this stage. Op-amp IC2 is a precision rectifier. It has a stage gain of R7/R6 to boost signal levels, the 1N4148 diode in the feedback loop now converts the audio signal into a positive half wave rectified signal. R4, R5 and C2 bias the non-inverting inputs of op-amps IC1 and IC2 to half the supply voltage. Peak signal levels pass through C5 and R8 to LED 1 which provides visual indication of peak levels. LED1 will not illuminate continuously but flash in response to peak sound. VR1 is adjusted so that LED1 flickers with each snore.
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