Simple Door Phone Intercom Circuit Schematic (Duplex)

A door phone intercom system provides a two-way conversation that is cost free. It can be very useful in hospitals, hotels and as a free of cost communication to a friend’s house.

Earlier I had already published another two way communication intercom circuit but it had the disadvantage of switching (same speaker is used both as mic and speaker based on the switch positions).

The main component used here in this two way intercom circuit is an 1895 IC. It is a 1 watt audio amplifier. Here we are using two condenser mics and two speakers for communication. Calling tone is generated by using melody generator IC UM66.

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50 watt power MOSFET amplifier circuit diagram

This is a MOSFET transistor based power amplifier circuit that can be operated between +35V to -35V range. The input voltage is pre filtered and pre amplified before applying to the MOSFET switch. The pre audio amplifier is a differential amplifier section with PNP transistor.

What is differential amplifier? A difference amplifier is a type of power amp with two differential inputs which amplify the difference between two input signals. Here we are dealing with the circuit diagram and working of high voltage differential amplifier using IRF9530 and IRF530 MOSFET. You need a dual power supply circuit for this amplifier which I had posted earlier.

Recommended: MOSFET Working Animation

Don't forget to have a look at other amplifier circuits in the related posts section at the bottom.

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2W battery powered portable audio amplifier circuit using TPA2025D1

Here we are dealing with a simple portable audio amplifier circuit using TPA2025D1 IC chip. The TPA2025D1 is a high efficiency Class-D audio power amplifier (mini amp) with battery tracking AGC (Automatic Gain Control) technology and an integrated Class-G boost converter that enhances efficiency at low output power. It drives up to 1.9 W into an 8Ω speaker (1% Total Harmonic Distortion- THD+N). With 85% typical efficiency, the TPA2025D1 helps extend battery life when playing audio. The most important applications of TPA2025D1 IC are cell phones amplifiers, PDA, GPS, (microphone) headphone amplifier circuits and portable electronics and speakers. You can construct this portable voice amplifier (mini power amp) with a cost around $1.5 (USD).

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Simple home audio power amplifier circuit schematic

Here is a new audio power amplifier schematic built around TIP darlington pair transistors. You can use this circuit for home audio power amplifiers and car audio amplifiers. The TIP142 and TIP147 darlington pair transistors forms a push pull high power amplifier configuration while the two BC558 PNP transistor provides a mini audio pre amplifier circuit. The audio signal is applied to the pre amp through a capacitor, then it is coupled to the push pull power amp via TIP141 transistor. The values and ratings of different components of power amplifier design are also given in this article. Implementation cost of this mini audio amplifier circuit is too cheap, near $5. The circuit can deliver 150 W RMS to a 8 Ω (150 Watt power amplifier).
Also Read:

• Mini audio amplifier 
• Simple FM transmitter circuit

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Op amp 741 Non Inverting Amplifier Circuit with Simulated Waveform

Non-inverting amplifier is one of the most popular op amp circuits similar to op amp inverting amplifier circuit. It provides a gain to the input signal without any change in the polarity. If a sine wave is fed to the input of this op amp non inverting amplifier, the output will be an amplified sine wave with zero phase shift. Here the input is applied to the non inverting terminal of the op amp. The non inverting amplifier gain is given by the expression A=1+Rf/Ri where Rf is the feedback resistance and Ri is the input resistance. The input impedance of non inverting amplifier is extremely large, typically 100MΩ.

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Simple portable Audio power amplifier circuit using LM386 IC

Here i-St@r comes with the simplest mini audio amplifier circuit schematic using LM386 low voltage audio power amplifier IC. This circuit is applicable to power medium sized speakers from a music player that can only drive earphones (lm386 headphone). The LM386 is a low voltage power amplifier IC designed for use in low voltage consumer applications. It can be used under battery operation and has a wide supply voltage range: 4V–12V or 5V–18V enabling us to use the circuit as a portable amplifier. Our simple audio amplifier has many applications, the common lm386 projects are AM-FM radio amplifiers, portable tape player amplifiers, intercoms, TV sound systems, line drivers, ultrasonic drivers, small servo drivers, power converters and much more.

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555 timer IC audio amplifier circuit schematics

Here we are going to discuss about a simple timer IC 555 project. The 555 timer IC can be used as an audio amplifier with astable multivibrator configuration. It functions as to carry out pulse width modulation (PWM) of audio signal. Current(I) capacity of 555 timer amplifier is 200mA which is sufficient to drive a small speaker. This simple 555 IC based amplifier circuit is a good substitute for conventional low power amplifiers. The low frequency audio signal is applied to the control voltage pin (5th pin) of 555 for pulse width modulation (PWM) generation. For beginners who want to know 'what is PWM?', read simple PWM modulation concept.

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Simple condenser microphone mini audio amplifier circuit schematic

This is a very useful and simple circuit diagram for amplifying weak signal from a capacitive condenser microphone. You can use this circuit for sound sensing applications and some automatic robotic sensors. We have already posted an efficient audio amplifier circuit using 1895 IC, it is somewhat complicated and is suitable for very sensitive applications. But this condenser microphone DIY audio sound amplifier is very small and simple to implement because it uses only two BC547 transistors and some discrete components. You can construct this circuit with a minimum price of $2. This circuit is apt for cheap amplification purposes in electronics such as pre amplifier for FM transmitters.

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Condenser Microphone Amplifier Schematic using BEL 1895 IC

Here I will show you an audio amplifier circuit that can be used for walkie talkies, low power transmitters, and packet radio receivers. A condenser mic audio amplifier gives good quality audio of 0.5 watts at 3 volts.   Here we are going to make use of BEL 1895 (Bharat Electronics Limited 1895) audio amplifier IC which is also a noise free amplifier IC. We are also using a pre amplifier section here to boost the weak signal from condenser mic. The pre amplified signal is connected to BEL 1895 audio amplifier IC. The preset in the first transistor acts as  a gain controller, it can vary the gain of amplifier circuit. PCB layout is also given below.

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Summing amplifier/ Inverting adder circuit using op amp 741

Summing amplifier or an adder is used to sum two signal voltages. Voltage adder circuit is a simple circuit  that enables you to add several signals together. It has wide variety of applications in electronic circuits. For example, on a precision amplifier, you may need to add a small voltage to cancel the offset error of the op amp itself. An audio mixer is another good example of adding waveforms (sounds) together from different channels (vocals, instruments) before sending the combined signal to a recorder.

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