Wireless Baby Monitor

Pradeep G. He is B.Sc. (Physics) and a regular contributor to international magazines. He is also a small-business owner in south India.

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This wireless baby monitor circuit using FM is designed to operate at a frequency of 100MHzefy tested. Its range of transmission is more than 100 metres with a 75cm wire antenna. The circuit is fully transistorised and so even a beginner can easily assemble it on a veroboard or the PCB whose pattern is given below for convenience.

Wireless Baby Monitor circuit

fig 1
Fig. 1: Circuit of the wireless baby monitor

Circuit diagram of the wireless baby monitor circuit is shown in Fig. 1. It is built around a condenser microphone (MIC1), transistors BC549 (T1 and T3) and BC557 (T2), along with a few other components.

parts listT1 and T2 provide high-gain audio to the VHF oscillator wired around T3. BC549 can oscillate well in VHF range. Frequency-modulated (FM) signals are transmitted through antenna ANT.1.

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By adjusting trimmer capacitor VC1, frequency can be set within 88MHz -108MHz band. Using a good FM radio (analogue type) receiver, transmitted signals can be heard. Do not use a mobile phone as receiver.

fig 2
Fig. 2: Inductor details

This unit with 9-volt battery can be kept near a baby’s bed. Any sound generated by the baby including a cry can be monitored wirelessly from another room. Readily available 1-micro Henry inductor can be used as L1. It can also be home brewed as shown in Fig. 2.

Construction and testing

fig 3
Fig. 3: PCB pattern of the wireless baby monitor

A single side PCB pattern of the wireless baby monitor circuit is shown in Fig. 3 and its component layout in Fig. 4. After assembling the circuit on a PCB, enclose it in a plastic case and keep it near the baby’s bed.

fig 4
Fig. 4: Component layout of the PCB

Download PCB and component layout PDFs: click here

The circuit works well off a 9V battery.


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13 COMMENTS

  1. Hello my name is Varun and I m making an Advanced Baby Bassinet and monitoring system.
    If i m not mistaken, the circuit shown above is to be kept near a baby. If so, then what will be used as a receiver ?
    If u have the circuit of that too please mail that photo or pdf to [email protected].
    Or u can mention about that in next months EFY issue as i have the subscription and i can read it from it.
    Please this info will be really helpful for my project.

    • In the above write up, its mentioned that you can use a normal FM radio receiver to receive the signals
      I copy the relevant para below:
      By adjusting trimmer capacitor VC1, frequency can be set within 88MHz -108MHz band. Using a good FM radio (analogue type) receiver, transmitted signals can be heard. Do not use a mobile phone as receiver.

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