Building intercom system is installed in each cell of the community station in the direction of Centre Administrator Tel, building entrances of Talkback host, electronic locks, door closer and user home intercom extension through private networks, for visitors and residents to speak.
Tenants can remote control to open the door, the unit companionway visitors through Talkback host call household, consent before entering the building, thus limiting illegal entry. At the same time, if unforeseen events, the household may also adopt the system notifies the security personnel to receive timely support and treatment. Currently, market building intercom, but due to its expensive, cumbersome, and many other reasons, limit its broad application. This article describes a new type of phone extension and details the type of extension sections of the design, its simple structure, convenient operation, low cost, has broad prospects.1 extension sections of the design
1.1 power
The power of the design as shown in Figure 1, the power to give circuit sections provide stable and effective working voltage, R1 is a resistance to 5 Ω, rated power of 2 W of resistance, external input, a voltage of 15 V, the divider R1, A1 to polar capacitors and capacitor C1 battery charging, ordinary while entering LM7805 voltage tube, then A2 to polar capacitors and ordinary capacitor C2 charging.
Experiment proves that, as long as the capacitance value select suitable, it will be at A point 12 V voltage values in point b is 5 v voltage values are voice circuits, and microcontroller as the operating voltage.
1.2 master circuit
Figure 2 is an extension of the main control circuit design, model selection AT89S52 microcontroller as control chip, the specific operation by writing programs.
As figure, when a staircase visitors through Talkback host call household, it signals that a figure in the bottom-right corner of 485 and then pass through MAX485 chip-chip, microcontroller receives the signal AT89S52 will be under the control of the program, P24 pins have a high level, and then through resistance transistor T3 provides base current, T3 breakover, rings, sounds, call household. Residents heard Bell, you can choose 3 different operation modes: unlock, monitoring, call. "Unlock" i.e. to single-chip and control circuit issued an order to directly open danyuanmen, let visitors came in, this applies to emergency situations. "Monitor" that is, to open a video device and to be installed in front of the camera to issue commands to start, and then install the monitor in your home so that the residents will see cell door, that is to see who's visiting, this process of implementation is by driving P11 mouth output circuit, as shown in Figure 3. "Call" that is, start the audio track and visitors for a call, the process of implementation is by driving P10 mouth output circuit, as in Figure 4, Figure 5 shows.
These three kinds of action, regardless of which households, AT89S52 microcontroller, P15 P14 P13, three pins, no matter which pin is inserted into the drawing, the microcomputer is low level under programmatic control in P26 pin results in a low level, the busy indicator light, indicating the households extension is working.
1.3 video circuit
When households "monitor" actions of the driver video circuit, as shown in Figure 3, in A combined with the fact that the operating voltage of 15 V, Figure 2 in the "monitor" button is pressed, the P11 mouth will produce a high level, by providing resistance to T1, T1 base current conduction, T2 tube, and will have a base current, T2 breakover voltage in LM7812 tubes 1 port, 15 V voltage after a pipe pressure drop is still virtually around the 15V, after LM7812 voltage tube, 3 port will be able to get a more stable voltage values, to monitor provides stable operating voltage, monitor 3, 4-port used to receive transferred from the camera so that tenants can monitor see cell door.
1.4 audio circuits
When the user makes a "call", the driver audio circuit, as shown in Figure 4.
Similarly, P10 mouth to produce a high level of on-T2 and T3, B point plus 12 V voltage, C point will receive roughly 12 V voltage value for audio circuits provide operating voltage.The main part of the audio circuit shown in Figure 5, Figure 4 the VDD voltage after voltage processing and access to that line.
As figure, tenants of live tube MIC, microphone, voice of the electrical signal into line with become, after entering polar capacitors C31, its amplifier U6A magnification by adjusting the resistance value of R38 and R42. Signal U6A enlarged to its 1 port, and then the follower U6C output to D-side, and then converted to a sound signal, allows visitors to hear. If the guest to speak, their sound processing to electrical signals after you enter from D-side, after entering polar capacitors C34, its amplifier U6C magnification by adjusting the resistance value of R45 and R46. After the transmission signal amplification to E point, and then converted to a sound signal, after the speaker output, let tenants heard. This enables residents and visitors in dialogue.2 simulation testing
2.1 wave test
First, use Multisim software on line for input and output waveforms.
Vocal frequencies in 90 ~ 3 000 Hz range selection in this article as from 1 000 Hz frequency test, as shown in Figure 5, in MIC-input 1 000 Hz isString wave, the equivalent of households speak to visitors, adjust the resistance of R38 and R42 that magnification of U6A is 12, the D Terminal resulting output waveform as shown in Figure 6.
If visitors on household words, equivalent to a d-side input sine wave, adjust the resistance of R45 and R46 makes U6B magnification of 2, may order the E-get an output waveform, as shown in Figure 7.
Because of the noise capacitance C35, output waveform than input waveforms may delay, you can adjust the size of C35 capacitance value to control the time delay.
2.2 real test
The line sections made of circuit boards, assembled into complete machine and write program programming into AT89S52 microcontroller made in the lab, complete testing.
Test results show that this type of good sound quality, real-time performance.3 conclusion
The line has passed the test in the laboratory.
The results showed that the models are compact, sounds good with enlarged authenticity, no noise, real time, met the design of the day.
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