Building intercom system audio circuit design

Building intercom system audio circuit design:

Building intercom audio circuit structure in General can be divided into two types of uplink signals and downlink signal separately as two line transmission, then the same line up and down line signals transmitted simultaneously.

Uplink signals and downlink signal separately as two line transmission, have the circuit is simple, good effect of transmission, defect a is a transmission line, the second is the networking problems.

The same line and bottom line signals transmitted simultaneously, in order to make the uplink signal downlink signal interference, eliminating side tone circuit, circuit complexity, design is not good effects, or even cause whistling.

The advantage is the connection of simple, non-visual design in two-wire connection, regardless of a line, just like a telephone. Because a signal lines and ground, so the networking easier.

Independent straight talk by multiple lines are mostly using the former, even network uses the same cable transmission mode.

With the cable transmission side silencers good or bad is the key to the audio effect.

Familiar with all of the telephone to have an understanding of this part of the circuit, knowing that this section is not easy to do.

Let us first review the following telephone standards, in which we can look at which copying is different.

Telephone direct resistance less than 350 Euro (dialup), on line impedance 600 euro.

Central Office AC impedance is 600 euro. Wires length 0-5 km. Line resistance 0--2 kilohms (double).

Reference phone network, building intercom network use telephone line transmission, also want to designed 600 euro.

However, building intercom connection typically do not like the phone, or even can not remember line resistance (and 600 euro). While the phone is a point-to-point communication, building without design floor decoder, an audio bus may pass several households.

Telephone Central Office is in the ring, dialing, call, on line impedance is unchanged (600 euro), thus eliminating side tone circuit in different States can be a very good performance.

In designing the building intercom, you must take this into account. Otherwise there is mention of machine called machine, dialing, listen back to Bell calling machine, call call machine cannot take account of the phenomenon.

To this end, we request design call circuit in the machine hang on line impedance not affected, that is to call the circuit is the high-impedance state, instead of the telephone of 600 euro.

All the machines in the on-hook State also represents a high impedance, parallel to a value greater than greater than 600 euro,

How to reach high design call circuit hire State?

General telephone circuits in electronic switches, has three branches: 1 send transistor collector, 2 receive cut side tone resistance, resistance through 680 Euro 3 the power supply, telephone why input impedance 600 Europe? is the third part of the results of the impedance parallel, send transistor collector output impedance = high resistance, sound resistance received cut side = some 680 K and European input impedance 600 European resistance.

Know the phone input impedance is how to control it, you can design a high-impedance circuit of the call.

Just remove the 680-European resistance, turning on logging code above, remove 10K resistance is very good building intercom call circuit.

Said country, because normal call circuit not too long, you can set parameters, in to the audio line power design la circuit impedance is 600 euro, you can, to all send circuit, load impedance is 600 euro, not the number of users with access.

Balancing arc side tone circuit just fine.

We all know that the phone is online on the road direct from electrical work, cancel 680 euro resistance, how to get electricity online? should be able, to send voice, receiver tandem circuit (most phones are like this), the current first through the circuit and then sent to the receiver on the ground, in receiving circuits for power, sufficient 386 zoom used.

Recommendations designed to 40MA 5. 1V supply capability.