- Snore – the outcome sound of an obstruction in air passage during breathing while sleeping which causes the respiratory structures to vibrate
- Light Emitting Diode (LED) – a semiconductor diode that is commonly a source of light when electric current pass through it
- 555 Timer – an 8-pin electronic device used in several mixtures of applications involving multivibration and timing operating modes
- Operational Amplifier (Op-Amp) – a differential amplifier having a large voltage gain, very high input impedance and low output impedance
- Electret Microphone – a type of condenser of capacitor microphone that utilizes a permanently charged object to eliminate the use of a power supply
The operation of the alarm is depends on several adjustments of the components. The variable resistor VR2 will designate the preset period of triggering the alarm while variable resistor VR1 controls the volume of the snore. The threshold control will set the triggering of the alarm since a snore is a continuous sound lasting for several seconds. It has a set delay so it will not activate with short noises such as car horns, doors slamming, and others. As the circuit gets activated, the vibrations will work gently to wake the snorer or force him to change his sleep posture.
To illustrate the scenario in general, the circuit may be divided into four partitions, according to the sequence of operation, using a low pass filter, precision rectifier, delay-on circuit, and timer and motor drive. An electrets condenser microphone functions as the input transducer to the amplifier and low pass filter around the op-amp circuit of IC1 to filter out high frequency noises by reducing the amplitude of frequencies higher than the frequency response limit of the system. It will only allow the passage of low frequencies. The precision rectifier made by op-amp IC2 converts the amplified sound to DC which will be filtered again. This should go on for a few seconds so the delay circuit will be activated. Op-amp IC3 comprises the delay circuit and will function as a level shifter by comparing the reference input set by the threshold control VR2 to the charge on capacitor C8. The timer and motor drive will be triggered upon reaching the threshold. The potentiometer R15 can be made to adjust the delay of the motor to start running.
To illustrate the operation of the circuit in detail, it starts as the sound is received by theECM microphone followed by amplification from the op-amp IC1, reducing high frequency gain and acting as an active low pass filter. It is possible to utilize a dynamic microphone with the elimination of resistor R1. The gain at low frequencies is inversely proportional as frequencies rise above 1 kHz and the level is controlled by VR1. The conversion of audio signal happens in op-amp IC2 as it functions as a precision rectifier to boost the signal levels by having a gain ratio of R7/R6. The feedback loop contains the diode 1N4148 that is accountable for producing a positive rectified signal from the conversion of audio signal. The non-inverting inputs of op-amps IC1 and IC2 is biased by C2, R4 and R5 to half the supply voltage. The visual indication of peak levels will be supplied by LED1 by showing a flash instead of continuous illumination. These peak signals are fed by R8 and C5 to the LED1. The flashing of LED1 by each snore is modified by VR1.
The delay is crucial to the circuit so that the alarm will not be triggered with any form of background noise. It will only be triggered after the snoring is started. The need for an input delay is important so the alarm will not set off in the middle of the night with a car door opening or a car horn. The alarm employs high frequency roll-off so as not to get affected by other sound with fundamental frequencies or harmonics. C8 and R12 provide the input delay. Capacitor C8 has a value of 33 uF as an electrolyte capacitor. It will start to charge slowly when using the half wave rectified signal from IC2. Without any signal, C8 will not charge and will discharge via R11 and R12. The combination of R9, R10 and D2 provides further rectification of the input signal and causing 1N4148 diode D2 to conduct with a little forward bias. This will also cause C8 to pre-charge even without a signal.
Since op-amp IC3 functions as a variable level detector, it also provides the delay while the threshold is controlled by VR2 for the capacitor C8 to have a voltage charge equal to the pin 3 of the op-amp. With this event, LED2 will indicate the triggering of the circuit which will cause the normally high IC3 to change to low output. The charging of the capacitor can be computed only when a fixed DC current is used but will not be possible on this circuit since the intermittent snore provides the charging current.
The delay circuit output is normally high on during the triggering stage and will change shortly when the prolonged snore is being identified. The change will trigger IC4 555 timer because of the correct polarity as the IC functions in monostable mode. A delay of 24.2 seconds can be obtained from the values of C9 and R15. Loads of up to 200 mA can be driven by the 555 timer output while transistors Q1 and Q2 can source up to 3 A. The power dissipated on the load and will not require heatsinks when both transistors are ON.
During the construction of the circuit some key points should be considered. A motor with high power and high torque should not be used. Similarly, the motor must not exceed 1 A of current from the power supply. However, a 9 V or 12 V electric motor is preferred. A resistor can be added in series with the motor if it is producing excessive vibration. Using a multimeter while the motor is running can measure the value of the DC current. If the motor would draw a current less than 200 mA, as supplied by the 555 timer, then it won’t be necessity for R16, Q1 and Q2.
Short flashes are produced by LED1 to indicate the peak detection of the sound. This detection can be adjusted by VR1 which will charge capacitor C8 slowly. The threshold to allow the circuit to trigger after a few seconds is adjusted by VR2. This triggering is indicated by LED2. The capacitor C8 will start to decompose during the interval between snores. Because of this, the circuit will not give false alarm with any surge of short noise.
Snoring can be caused by a lot of factors and reasons the can be out of our control such as allergies, asthma, a cold, sinus infections, being male, being middle aged or beyond, or hereditary. It can also be within our control such as sleeping posture, alcohol or medications, a history of smoking, and being out of shape or overweight. The blockage in irregular flow of air may be due to obstruction in the nasal passageway, fat gathering in and around the throat, mispositioned jaw due to tension in the muscle, and throat weakness which causes the throat to close during sleep.
Despite of this snore alarm circuit, there are still natural ways of preventing or reducing the snoring like losing weight, clearing the nasal passages, avoiding certain foods, medications and alcohol before bed, elevating the head of the bed, and sleeping on your side. A circuit similar to this can also detect if an infant sleeps on his back.