This door phone circuit allows the house owner to converse and acquire the required information (e.g. who he is and what is the purpose of his visit etc.) before opening the door to a visitor.
The phone incorporates an in-built musical doorbell. It allows a two-way conversation and can operate on mains or a 9volt battery. The complete phone cost works out to be unbelievably low. Also, this circuit is quite helpful at the time of coronavirus pandemic. This circuit is helpful in maintaining social distancing with strange and unknown peoples which may be carriers of the virus.
Door Phone Circuit Diagram:
Components For Simple Door Phone Circuit:
Semiconductors
IC1 IC1895
IC2 UM66
D1 4.7V, 250 mW
Resistors (all 1/4 watt, 5%)
R1 3.3k
R2, R5 390 ohms
R3 100k
R4 47 ohms
Capacitors
C1 0.22uF
C2 100uF
C3 10uF
C4 470pF
C5 220uF
C6 330uF
Miscellaneous
M1, M2 Condenser microphones
LS1, LS2 2 ohms, 1 watt Speaker
PCB
Cabinet
etc.
Working of Door Phone Circuit:
The circuit is based on1895 audio amplifier IC. Resistor R1 biases the two microphones.
The call tune is generated by the 64-tone ROM IC2, the output of which is fed to IC1 through C1. Capacitor C6 serves as the output coupling capacitor. D1 and R3 drop the voltage for IC2.
This circuit is divided into 3 parts- Input stage, Amplifier stage, and Output stage.
- In the first stage mics and the tone generator are present. The output of tone generator IC UM66 is connected parallel with the condenser mic for amplification.
- The second stage contains an amplifier that consists of the amplifier IC 1895 which amplifies the inputted signal. IC195 is a 1W power Ic.
- Two 8-ohm speakers connected in parallel In the output stage. They reduce the total impedance to 4 ohms, in order to match impedance between the speaker and the amplifier IC. So there is maximum power transfer.
Construction:
The complete circuit can be assembled on a PCB and can be fixed on the gate post in a cabinet, preferably of plastic. The speaker and mike should be fixed behind the panel frame near the push button. The mike M2 and speaker LS2 can be kept in a suitable cabinet. The door phone is ready to use.
Power Supply Circuit:
Components for Power Supply:
Semiconductors
BR1 CSB bridge rectifier
Capacitors
C1 1000uF (10V electrolytic)
Miscellaneous
X1 Primary 230 volts ac, secondary 9 volts @ 100mA
Alternate of Power Supply:
