Click para ampliarParty Line Intercom
A large number of intercom stations can be tied together. All units are connected in parallel, and the entire system is buzzed by only one signaling circuit. Each unit is powered individually from 1.5-V cells for redundancy. For greater signal volume, 3-V sources can be used for the supplies without changing any other parts of the system. The carbon microphone of a standard telephone handset at each station feeds into a common-base amplifier, and a tandem high-gain common-emitter stage drives the intercom line. All phone earpieces are in parallel across the line. The signaling circuit, also connected across the line, is a simple oscillator that gives all the earpieces.
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Click para ampliarOne Way, Voice Activated Intercom
An omnidirectional electret microphone can be used to pick up the sound and convert it into an electric signal. The output of the microphone is fed along two paths. In the first path, the signal is send to the inverting input at pin 6. In the second path, the microphone signal is fed to the non-inverting input of U2, where it is amplified and output to the speaker, SPKR1.
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Click para ampliarIntercom 2
This intercom uses a single audio IC as a two-way amplifier, and the speakers as microphones. A single 6-V supply provides adequate audio volume.
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Click para ampliarIntercom
The circuit consists of separate amplifiers--one for each station--rather than a single amplifier and a time sharing arrangement. U1 and U2 are low-voltage audio amplifiers, each of which operates as separate entities with switches at either station controlling which will transmit or receive. With capacitors C7 and C8 included in the circuit, the amplifiers have a gain of 200. Omitting those two components drops the gain to about 20. Other gain levels are available with the addition of a series-connected R/C combination connected between pin 1 and pin 8--for example, a 1000 ohm resistor and 10 uF capacitor for a gain of about 150.
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Click para ampliarHands Off Intercom
Amplifier A increases the microphone's output to a usable level. The output signal is fed to op amp B, which inverts the signal 180 degrees. A balance-control potentiometer connects across the outputs of amplifiers A and B. If an audio tone is fed into the microphone and the balance potentiometer's wiper is all the way over to the A output position, the tone will be heard at high level. As the wiper is rotated toward the B output, the audio level will decrease until it just about disappears near the center of the potentiometer's range. As you continue to rotate the wiper, the signal will begin to increase once again. With the balance control set for a minimal output, the intercom's tendency to self-oscillate from acoustical feedback between the microphone and speaker is kept to a minimum. The microphone's amplified signal at A's output is fed to the other intercom through the audio in/out cable. Since both intercom units are alike, the
audio information coming from one unit feeds the other at the input of op amp B. The incoming audio is amplified slightly by op amp B and the output signal is sufficiently increased by the power amp to drive the speaker.
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audio information coming from one unit feeds the other at the input of op amp B. The incoming audio is amplified slightly by op amp B and the output signal is sufficiently increased by the power amp to drive the speaker.
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