Alarm Circuit for Snoring Prevention by 555 Timer

The circuit was designed
to produce a circuit that will alarm a sleeping person to prevent
snoring by using a vibrator instead of an audio alert so as not to
affect the whole household. It contains a trigger indicator, peak
display indicator, a level control and a variable trigger threshold. A
small motor enclosed in a film case with of 35 mm in size, will provide
the vibration and suitably positioned under the pillow or mattress.

  • Snore – the outcome sound of an obstruction in air passage during
    breathing while sleeping which causes the respiratory structures to
  • 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.


Circuit diagram

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 the ECM
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

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

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.

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