This Two-Way intercom might save you time if you need to get up regularly to speak with someone in your office. To communicate, simply turn it on from both sides. It can also be useful if you have someone at home who is experiencing Corona. Figure 1 shows a block diagram of the intercom.
The intercom’s circuit diagram is depicted in Fig. 2. Two condenser microphones (MIC1 and MIC2), four 2N2222 transistors (T1 through T4), and two LM380N audio amplifiers make up the simple, low-cost intercom (IC1 and IC2).
A condenser microphone is similar to a capacitor (also known as a condenser) with two parallel plates near to each other. One of the plates functions as a diaphragm and is constructed of extremely light and thin material. When sound waves strike the diaphragm, it vibrates, changing the distance between the two plates and thus adjusting the capacitance. The ensuing capacitance variation generates an electrical signal, which is then amplified.
Because most intercoms don’t have a pre-amplifier circuit, the sound output is distorted. Pre-amplifiers are used in this circuit to boost the inputs for loud and clear sound from the loudspeakers.
There are two similar circuits, as shown in Fig. 2. R1 serves as a current-limiting resistor for MIC1 in the lower circuit. Sound’s electrical signal passes through coupling capacitor C1, which blocks all DC signals and only allows AC signals to pass. The amplifier portions produced by transistors T1 and T2 and IC LM380N increase this signal.
The signal is first amplified by an amplifier based on transistor T1 and then amplified again by a second amplifier based on transistor T2. T2’s output at the collector is routed to the LM380N (IC1) via pin 2, capacitor C5, and the pot VR1.
The sound is reproduced using an 8-ohm speaker (LS2) linked to the LM380N output through capacitor C7 and resistor R12. The upper and lower sections of the circuit each require a 9V regulated supply or a 9V battery.
The circuit’s upper part is identical and operates in the same way. Your voice can be heard via speaker LS2 when you talk in front of microphone MIC1. Your voice can also be heard from speaker LS1 when you talk in front of microphone MIC2. As a result, two-way communication is feasible.
Construction and testing
Using a PCB or a general-purpose board, assemble the circuit. Along the dotted line on the PCB, cut it into two sections (SET1 and SET2). Separate each PCB and place it in an appropriate box. SET1 should be in one room, while SET2 should be in another. Using a twin wire, connect LS2 in SET1 in the first room to SET2 in the second room, and LS1 from SET2 to SET1 in the first room.
Fix MIC1 to the front of the SET1 enclosure and LS2 to the back. Similarly, attach MIC2 to the front and LS1 to the back of the SET2 container. To begin communication on both sides, turn on S1 in SET1 and S2 in SET2.
When you talk into microphone MIC1 in SET1, you will be heard through loudspeaker LS2 in the second room. Similarly, you will hear him talk into microphone MIC2 over loudspeaker LS1.
If the microphone and loudspeaker are near to each other and facing each other, there will be acoustic feedback. As a result, when building and installing microphones and loudspeakers on the enclosures, ensure a safe distance between them.