Monitor and Look Out Circuit for Infant/Baby

Monitor and Look Out Circuit for Infant/Baby

Circuit Project Description

The circuit was designed for the sole purpose of making a way to watch over a baby while he is left alone in his room.

Terminology TL072 – a low noise JFET input operational amplifier with features such as common-mode input voltage range, high slew rate, operation without latch up, compensated internal frequency, high input impedance at the JFET input stage, low noise, low total harmonic distortion, protected from output short circuit, low input bias and offset currents, wide common-mode and differential voltage ranges, and low power consumptionBD139 – NPN power transistor used for driver stages in hi-fi amplifiers and television circuits because of its low voltage at 80 V maximum and high current at 1.5 A maximumElectret Microphone – a type of condenser of capacitor microphone that utilizes a permanently charged object to eliminate the use of a power supply Circuit Explanation

For mothers who are very busy on their household chores, this simple circuit is advisable for monitoring their newborns and older babies which are a few rooms away. It consists of a transmitter with the use of an electret microphone M1 that is placed near the child while the receiver consists of a speaker located near or carried by the mother or the person taking care of the baby. Other designs are coming as bi-directional with the use of transceivers while others are having music to be played to the baby, having two receivers, having a visible signal or a set of lights to indicate the noise level, having a vibrating alert, or having a movement sensor on the transmitter side. Any design can be used for as long as they serve the main purpose of the circuit which is to allow attendants to hear the baby when it wakes up or cries.

The gain of the circuit depends on the value of the resistor R1. This resistor can be replaced by a potentiometer or a trimmer to meet the required values. Within the region of relay RL1 is a small automatism circuit which has a constant and continuous intermittence on a transistor output. The intermittence speed is regulated by a potentiometer or fixed resistors. The supply of the circuit is provided by a 9V battery source. It can also take its power from the AC line while the battery acts as a standby power source. The life of the battery during the operation is large enough to handle the circuit since the current consumption is only minimal at about 30 mA for the 8R loudspeaker which has 0.4 W of power.

The transistors involved in this circuit do not require a heatsink since they do not consume more power. They are operating in class B mode where they are never conducting at the same time. Because of this, the transistors save energy and decreases heat dissipation.

Part List

C2-3-6=100nF/100V MKT
C11=100nF/100V MKT
LD1=Led 3mm RED
RL1=Small RELAY 12V DC
F1=Fuse 0,1A
P1=470kohms Trimmer or potesiometer
TR1=220Vac/9V 0,2A Transformer
M1=Electret condenset Microphone
S1=2X2 1A SW
BATT=9V Battery 


In the present technology, some baby monitors comes with digital LCD, wireless capability, with photo frame, live video camera, water resistant, adjustable brightness and alarm volume, and capability of desktop stand and wall mounting. The concept of this circuit can also be used on monitoring rooms remotely with included audio observation from kids, nannies, spouses or other family members at home. They can also be applied not only in homes but also in offices and businesses to provide security.


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