CN102457621B - Single-board type command amplification board - Google Patents
Single-board type command amplification board Download PDFInfo
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- CN102457621B CN102457621B CN201010510976.5A CN201010510976A CN102457621B CN 102457621 B CN102457621 B CN 102457621B CN 201010510976 A CN201010510976 A CN 201010510976A CN 102457621 B CN102457621 B CN 102457621B
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Abstract
The invention relates to a single-board type command amplification board. A peripheral microprocessor, an audio power amplifier, a signal tone generator, a busy tone and mute detection circuit, an off-hook and on-hook detection circuit, a constant current source feed circuit, a ringing detection circuit, a communication equipment user port, a telephone set port, a broadcasting speaker port and a power supply circuit are arranged on a printed circuit board. The single-board type command amplification board is also additionally provided with an audio power amplifier processor, an amplitude limiting circuit, an audio power amplifier protection and line protection circuit, a power-off switching circuit, a two/four-wire switching and called mode selecting circuit, a microphone interface circuit and a microphone interface and double audio detection circuit. The single-board type command amplification board has reasonable structure, and not only can be matched with communication equipment which meets the national standard, but also can be used for independently forming a novel conference terminal. The multifunctional selectivity and the stability and the reliability of the operation of the single-board type command amplification board are obviously improved.
Description
Technical field
The invention belongs to communication equipment technical field, relate in particular to a kind of feature board in communication equipment, specifically refer to a kind of single-board type command amplification board.
Background technology
In enterprise production process, schedule job instruction is issued to each production station by dispatch control person by communication equipment, and especially to the large and spacious production environment post of on-site noise, instruction is promptly and accurately issued to on-the-spot for guaranteeing that safety in production plays an important role.Generally adopt the form of post situ configuration broadcast & call for the solution in the large and spacious production environment post of on-site noise.The 6th phase of in December, 2008≤Tianjin University of Technology journal >=27th volume the 65th, 66,67 pages of Guo Cui beautiful etc. deliver≤design >=article of audio-enlarging telephone based on AT89C2051 in, the hands free telephone that the employing single-chip microcomputer of author designed is control core, its technical characterictic: audio-enlarging telephone is made up of ordinary telephone set circuit and single chip machine controlling circuit.Ordinary telephone set circuit is made up of polar protective circuit, switching circuit, dial-up circuit, speaking circuit, ringing circuit etc.; Single chip machine controlling circuit is made up of AT89C2051 single-chip microcomputer, picking/hanging machine detection circuit, busy tone detecting circuit, ring detecting circuit, power amplifier, house dog and output control circuit etc.Described in article, in process of production, can under 110dB high-noise environment, realize clear call, reduce phone and miss, enhance productivity.But by analyzing the power circuit of hands free telephone, three kinds of power supply: 5V, 12V of work, 30V, must provide 220V AC power at the scene, could obtain by rectifying and voltage-stabilizing.Therefore due to the demand of scene power supply, cause field apparatus safety and problem with grounding, simultaneously impact to some extent under rugged environment in the useful life of equipment, particularly essential integral replacing hands free telephone after equipment breaks down.
In addition, someone has applied for the patent of invention of " a kind of Dictating user board " (patent No.: CN201336682Y) by name.It is characterized in that: on Dictating user board, be provided with CPU, audio frequency amplifier, tone generator, busy indicating circuit, pluck, on-hook detection circuit, constant current feed circuit, ring detecting circuit, busy tone detecting circuit, without tone detection circuit, group, exhale circuit, antipole testing circuit together, between them, interconnect by circuit, on Dictating user board, be also provided with three interfaces, be connected with loud speaker with program controlled automatic exchanger user port, telephone set respectively.It is mainly the accessory belonging in program control automatic instructure telephone device, and due to production scene adverse circumstances, Dictating user board is normally worked, and really accomplishes that reliable, stable and multi-functional selectivity fails to embody.
Summary of the invention
Technical problem to be solved by this invention is: overcome the deficiencies in the prior art, and provide a kind of rational in infrastructure, the single-board type command amplification board that technology is perfect, it can be supporting with the communication equipment that meets national standard, can form separately again new conference terminal, the multi-functional selectivity that it possesses and the stability of operation, reliability be improved significantly.
The technical solution used in the present invention is: on a printed circuit board, be provided with peripheral microprocessor, audio-frequency power amplifier, tone generator, busy tone and without tone detection circuit, picking/hanging machine detection circuit, constant-current source feed circuit, ring detecting circuit, communication device user port, telephone set port and broadcast speaker port, power supply circuits, the present invention is characterized in that: also have additional audio frequency power amplifier processor, amplitude limiter circuit, audio frequency power amplifier protection and circuit protection circuit, power failure change-over circuit, 2/4 conversion of line system and called mode selection circuit, microphone interface circuit, microphone interface and dual-audio testing circuit, tone generator output is connected to amplitude limiter circuit, amplitude limiter circuit output is connected to audio-frequency power amplifier, the input of tone generator is connected with peripheral microprocessor, constant-current source feed circuit is exported telephone set feed, and to telephone set dislodging machine testing, detection signal is connected to picking/hanging machine detection circuit, picking/hanging machine detection circuit output is connected to peripheral microprocessor, the output signal of communication device user port is connected to ring detecting circuit, ring detecting circuit output is also connected to peripheral microprocessor, the output signal of communication device user port is also connected to busy tone and without tone detection circuit, busy tone and be connected to equally peripheral microprocessor without the output of tone detection circuit, the input of dual-audio testing circuit connects communication device user port and telephone set port, and carry out dual-audio detection for communication device user port and telephone set, the output of dual-audio testing circuit connects peripheral microprocessor, the output of audio-frequency power amplifier is connected to audio frequency power amplifier protection and circuit protection circuit, audio frequency power amplifier protection and circuit protection circuit while and communication device user port, broadcast speaker port, telephone set port and power failure change-over circuit output connect, the output of constant-current source feed circuit connects power failure change-over circuit, meanwhile, audio frequency power amplifier processor output connects and controls the protection of audio-frequency power amplifier and audio frequency power amplifier and circuit protection circuit, audio frequency power amplifier processor is connected and is controlled by peripheral microprocessor output, 2/4 line system conversion and called model selection phone are by operator's toggle switch, its output is connected to peripheral microprocessor, power failure change-over circuit connects to be controlled constant-current source feed circuit connection telephone set feed or connects communication device user port connection telephone set feed, microphone is connected with microphone interface circuit, microphone interface circuit is connected with amplitude limiter circuit and audio-frequency power amplifier.
In technique scheme, described audio-frequency power amplifier adopts many zero potentials circuit.
Concrete grammar of the present invention is as follows:
1, the power supply of instruction amplification board adopts at machine room standard traffic Power supply, and peripheral microprocessor and peripheral circuit power supply provide by power circuit.
2, instruction amplification board is normally worked, and telephone set feed is provided by constant-current source on instruction amplification board.After instruction amplification board is due to fault power-off, by power failure change-over circuit, telephone set is transformed into communication device user port feed, guarantee the normal work of communication.
3, according to user's requirement, by 2/4 conversion of line system and called mode selection circuit, switching signal is delivered to peripheral microprocessor, determine mode of operation.
4,, under the called pattern of 4 line system, when user's called, can select first ringing telephone stations to be restarted broadcast or directly started two kinds of modes of broadcast.
5, in the time plucking on-hook signal generation, picking/hanging machine detection circuit is delivered to peripheral microprocessor by signal and is carried out respective handling.
6, when in the time having off hook signal to occur, the double-audio signal that peripheral microprocessor detects according to dual-audio testing circuit, judgement is that special function code or domestic consumer call out.
7, audio-frequency power amplifier starts and discharges by the control of Audio power amplifier processor.At audio-frequency power amplifier carry input terminal Finite Amplitude circuit, with protective circuit, improve the reliability of audio-frequency power amplifier work at audio-frequency power amplifier output.Audio-frequency power amplifier starts provides signal tone by signal tone circuit for generating, and voice are exported and delivered to Live Audio by audio-frequency power amplifier simultaneously.
8, in the time having busy tone or tone-off on circuit, busy tone and without tone detection circuit, signal is delivered to peripheral microprocessor and carry out respective handling.
9, all there iing over-voltage and over-current lightning-proof protection circuit with communication device user port interface with to on-the-spot telephone set port and Broadcast Port, guaranteeing instruction amplification board reliability.
10, provide microphone interface circuit, instruction amplification board is realized separately conference terminal machine function.
The present invention compared with prior art, has following features:
Identical point: 1, all adopt microprocessor as control centre unit.
2, in peripheral circuit, the detection of signal is possessed to tone generator, picking/hanging machine detection circuit, constant current feed circuit, ring detecting circuit, busy tone equally and without tone detection circuit.
3, the Peripheral Interface of printed board is connected with communication device user port, telephone set and broadcast.
Distinctive points: 1,, as a kind of instruction amplification board of communications device functions expansion, its supply power mode should be supporting with existing communication equipment, therefore adopts communication standard Power supply.Offer peripheral circuit power supply by power supply circuits on instruction amplification board, in instruction amplification board, peripheral circuit and audio-frequency power amplifier are normally worked in 24-60V supply district energy assurance system.
And instruction amplification board operational environment, at communication device room, has improved stability and the reliability of instruction amplification board.
2, increased audio-frequency power amplifier processor, the work of special disposal audio-frequency power amplifier and protection, increase instruction amplification board reliability.
3, audio-frequency power amplifier adopts many zero circuits, can effectively reduce noise and inhibition is uttered long and high-pitched sounds, and guarantees the stable of circuit; Output adopts constant-pressure type output, eliminates load and does not mate and produce the hidden danger that burns out audio-frequency power amplifier; Level pressure output bias is controlled at≤and 1%.
4, possess as instruction amplification board the interface being connected with communication device user port, telephone set and broadcast, except considering the reliability and stability of the product self designing, also must consider and when miscellaneous equipment interface and signal are transferred to broadcast and telephone terminal by circuit the interference problem (as line short, open circuit, overvoltage, overcurrent, lightning protection etc.) on circuit.And in the time going wrong, audio power amplifying circuit and output port are protected, could really accomplish the reliable and stable of instruction amplification board.In instruction amplification board circuit, audio frequency power amplifier protection and circuit protection circuit are increased; In audio power amplifying circuit, increase anti-microwave interference circuit, to improve the antijamming capability of instruction amplification board simultaneously.
5, the basic function that instruction amplification board is realized is that voice signal is outputed to noisy scene by audio power amplifying circuit, increases amplitude limiter circuit, reduces signal distortion, suppresses to utter long and high-pitched sounds, protection audio power amplifying circuit.
6, in order to promote instruction amplification board function, increase dual-audio testing circuit, double-audio signal on identification circuit, realizes telephone user and starts the broadcast in this post, or by curing alarm voice in remote activation signal tone circuit for generating, alarm voice broadcast service is arrived on-the-spot.
7,2/4 conversion of line system and called mode selection circuit, is the expansion to instruction amplification board function, and in the situation that not increasing hardware circuit, practical function maximizes.2/4 line change-over circuit processed is to consider under different mode, the selection of transmitting voice signal mode.Called mode selection circuit is according to user's field demand, to being first to ringing telephone stations or directly start audio power amplifying circuit signal tone and voice are delivered to the model selection of broadcast with broadcasting user.
8, microphone interface circuit is at instruction amplification board during separately as conference terminal machine, and in the time participating in a conference, user's speech is delivered in meeting group by microphone, realizes conference terminal function.
9, power failure change-over circuit is to guarantee after instruction amplification board is due to fault power-off, directly telephone set is linked into the user port of communication equipment, although lose instruction enlarging function, guarantees the basic communication functions of call site machine.
In sum: the instruction amplification board as a kind of communications device functions expansion is guaranteeing that the stability of a system and reliability are simultaneously; as machine room standard traffic Power supply, special Audio power amplifier processor, increase audio frequency power amplifier protection and circuit protection circuit, amplitude limiter circuit, power failure change-over circuit; also take into full account the maximization that function realizes; as increase dual-audio testing circuit, 2/4 line system conversion and called mode selection circuit, microphone interface circuit, for the Function Extension of user communication device provides a best choice.
Beneficial effect of the present invention: 1. instruction amplification board is concentrated machine room power supply, has improved the stability of product.2. on-the-spot post terminal forms simply, is made up of telephone and broadcast, easy to maintenance.3. perfect input and output are protected, and have guaranteed the reliability of instruction amplification board.4. expanded communications device functions, increased instruction amplification board and realize point-to-point broadcast call functions.5. possesses specific function code.6. realize telephone remote control.7. it can work alone, and forms novel conference terminal equipment.8. for providing several functions to select in the actual use procedure of user.
Accompanying drawing explanation:
Fig. 1 is structured flowchart of the present invention
Fig. 2 is power failure conversion and control schematic diagram
In figure: 1, peripheral microprocessor, 2, Audio power amplifier processor, 3, audio power amplifier circuit, 4, amplitude limiter circuit, 5, microphone interface circuit, 6, signal tone circuit for generating, 7, picking/hanging machine detection circuit, 8, constant-current source feed circuit.9, ring detecting circuit, 10, busy tone and without tone detection circuit, 11, dual-audio testing circuit; 12,2/4 conversion of line system and called mode selection circuit; 13, power failure change-over circuit, 14, audio frequency power amplifier protection and circuit protection circuit, 15, instruction amplification board; 16, communication device user port; 17, broadcast, 18, telephone set, 19, microphone; 20, power supply circuits, 21, data/address bus.
Embodiment:
Referring to Fig. 1, on a printed circuit board, be provided with peripheral microprocessor 1, audio-frequency power amplifier 3, tone generator 6, busy tone and without tone detection circuit 10, picking/hanging machine detection circuit 7, constant-current source feed circuit 8, ring detecting circuit 9, communication device user port one 6, telephone set port one 8 and broadcast speaker port 17, power supply circuits 20, the present invention is characterized in that: also have additional audio frequency power amplifier processor 2, amplitude limiter circuit 4, audio frequency power amplifier protection and circuit protection circuit 14, power failure change-over circuit 13,2/4 conversion of line system and called mode selection circuit 12, microphone interface circuit 5, microphone interface and dual-audio testing circuit 11, tone generator output is connected to amplitude limiter circuit 4, amplitude limiter circuit output is connected to audio-frequency power amplifier, the input of tone generator is connected with peripheral microprocessor, constant-current source feed circuit is exported telephone set feed, and to telephone set dislodging machine testing, detection signal is connected to picking/hanging machine detection circuit, picking/hanging machine detection circuit output is connected to peripheral microprocessor, the output signal of communication device user port is connected to ring detecting circuit, ring detecting circuit output is also connected to peripheral microprocessor, the output signal of communication device user port is also connected to busy tone and without tone detection circuit, busy tone and be connected to equally peripheral microprocessor without the output of tone detection circuit, the input of dual-audio testing circuit connects communication device user port and telephone set port, and carry out dual-audio detection for communication device user port and telephone set, the output of dual-audio testing circuit connects peripheral microprocessor, the output of audio-frequency power amplifier is connected to audio frequency power amplifier protection and circuit protection circuit, audio frequency power amplifier protection and circuit protection circuit while and communication device user port, broadcast speaker port, telephone set port and power failure change-over circuit output connect, the output of constant-current source feed circuit connects power failure change-over circuit, meanwhile, audio frequency power amplifier processor output connects and controls the protection of audio-frequency power amplifier and audio frequency power amplifier and circuit protection circuit, audio frequency power amplifier processor is connected and is controlled by peripheral microprocessor output, 2/4 line system conversion and called model selection phone are by operator's toggle switch, its output is connected to peripheral microprocessor, power failure change-over circuit connects to be controlled constant-current source feed circuit connection telephone set feed or connects the feed of communication device user port to telephone set, microphone is connected with microphone interface circuit, microphone interface circuit is connected with amplitude limiter circuit and audio-frequency power amplifier.
When called: instruction amplification board 15 is connected with communication device user port one 6, by power supply circuits 20, ring detecting circuit 9 detects the ringing signal of user port, delivering to peripheral microprocessor 1 processes, according to the model selection of 2/4 line system conversion and called mode selection circuit 12, result is delivered to Audio power amplifier processor 2, start audio power amplifying circuit 3, enabling signal sound circuit for generating 6 simultaneously, signal tone and voice are by amplitude limiter circuit 4, audio frequency power amplifier protection and circuit protection circuit 14, power failure change-over circuit 13 is transmitted and is delivered to Live Audio 17 by circuit, realize caller voice and deliver to Live Audio after amplifying.
Call site machine 18 off-hooks, protect and circuit protection circuit 14, power failure change-over circuit 13, constant-current source feed circuit 8, picking/hanging machine detection circuit 7 by audio frequency power amplifier, deliver to peripheral microprocessor 1 and process, telephone set 18 and calling subscriber's call.Calling subscriber's on-hook is by busy tone and deliver to peripheral microprocessor 1 without tone detection circuit 10 and process, and discharges audio power amplifying circuit 3 by Audio power amplifier processor 2.Constantly detect audio frequency power amplifier protection and circuit protection circuit 14 at communication process sound intermediate frequency power amplification processor 2, play reduction noise, suppress to utter long and high-pitched sounds, guarantee to transmit clear voice in circuit, protect audio power amplifying circuit 3 normally to work simultaneously.
When caller: telephone set 18 off-hooks, by audio frequency power amplifier protect and circuit protection circuit 14, power failure change-over circuit 13, constant-current source feed circuit 8, dual-audio testing circuit 11 detection lines on double-audio signal, deliver to peripheral microprocessor 1 and process, internal user number is called out other internal user in this way; Special code starts audio power amplifying circuit 3, signal tone circuit for generating 6 by Audio power amplifier processor 2 in this way; complete self-starting function, signal tone and voice are transmitted and are delivered to Live Audio 17 by circuit by amplitude limiter circuit 4, audio frequency power amplifier protection and circuit protection circuit 14, power failure change-over circuit 13.Constantly detect audio frequency power amplifier and protective circuit 14 at communication process sound intermediate frequency power amplification processor 2, play reduction noise, suppress to utter long and high-pitched sounds, adjust amplifying circuit parameter, guarantee to transmit clear voice in circuit, protect audio power amplifying circuit 3 normally to work simultaneously.
In caller or called communication process, dual-audio testing circuit 11 can detection line on double-audio signal, deliver to peripheral microprocessor 1 and process, special code can also start the voice signal that is pre-stored in signal tone circuit for generating 6 in this way, realizes remote control function.
While doing conference terminal: instruction amplification board 15 is connected with communication device user port one 6, microphone 19 is connected with microphone interface circuit 5; microphone voice are by microphone interface circuit 5, amplitude limiter circuit 4, audio power amplifying circuit 3, audio frequency power amplifier protection and circuit protection circuit 14; deliver to respectively broadcast 17 and conference users, realize conference speech function and listen to conferencing function.Constantly detect audio frequency power amplifier protection and circuit protection circuit 14 at communication process sound intermediate frequency power amplification processor 2, play reduction noise, suppress to utter long and high-pitched sounds, guarantee to transmit clear voice in circuit, protect audio power amplifying circuit 3 normally to work simultaneously.
In the time that power supply circuits 20 break down; telephone set 18 is protected with circuit protection circuit 14, power failure change-over circuit 13 and is directly connected with communication device user port one 6 by audio frequency power amplifier; guarantee that instruction amplification board 15 is due to after fault power-off, the normal work of call site machine 18 communication.
Referring to Fig. 2, illustrate for power failure change-over circuit 13 circuit:
Under instruction amplification board 15 normal operation, by power failure change-over circuit 13, audio frequency power amplifier protective circuit and circuit protection circuit 14, constant-current source current feed circuit 8 is powered to telephone set 18; When 15 power supplies of instruction amplification board have not had, power failure change-over circuit 13 is directly received communication device user port one 6 by telephone set 18 by audio frequency power amplifier protective circuit and circuit protection circuit 14, and the communication of assurance call site is normally worked.
Claims (2)
1. a single-board type command amplification board is provided with peripheral microprocessor, audio-frequency power amplifier, tone generator, busy tone and without tone detection circuit, picking/hanging machine detection circuit, constant-current source feed circuit, ring detecting circuit, communication device user port, telephone set port and broadcast speaker port, power supply circuits on a printed circuit board, it is characterized in that: also have additional audio frequency power amplifier processor, amplitude limiter circuit, audio frequency power amplifier protection and circuit protection circuit, power failure change-over circuit, 2/4 conversion of line system and called mode selection circuit, microphone interface circuit, microphone interface and dual-audio testing circuit, tone generator output is connected to amplitude limiter circuit, amplitude limiter circuit output is connected to audio-frequency power amplifier, the input of tone generator is connected with peripheral microprocessor, constant-current source feed circuit is exported telephone set feed, and to telephone set dislodging machine testing, detection signal is connected to picking/hanging machine detection circuit, picking/hanging machine detection circuit output is connected to peripheral microprocessor, the output signal of communication device user port is connected to ring detecting circuit, ring detecting circuit output is also connected to peripheral microprocessor, the output signal of communication device user port is also connected to busy tone and without tone detection circuit, busy tone and be connected to equally peripheral microprocessor without the output of tone detection circuit, the input of dual-audio testing circuit connects communication device user port and telephone set port, and carry out dual-audio detection for communication device user port and telephone set, the output of dual-audio testing circuit connects peripheral microprocessor, the output of audio-frequency power amplifier is connected to audio frequency power amplifier protection and circuit protection circuit, audio frequency power amplifier protection and circuit protection circuit while and communication device user port, broadcast speaker port, telephone set port and power failure change-over circuit output connect, the output of constant-current source feed circuit connects power failure change-over circuit, meanwhile, audio frequency power amplifier processor output connects and controls the protection of audio-frequency power amplifier and audio frequency power amplifier and circuit protection circuit, audio frequency power amplifier processor is connected and is controlled by peripheral microprocessor output, 2/4 line system conversion and called model selection phone are by operator's toggle switch, its output is connected to peripheral microprocessor, power failure change-over circuit control constant-current source feed circuit connects telephone set feed or connects communication device user port connection telephone set feed, microphone is connected with microphone interface circuit, microphone interface circuit is connected with amplitude limiter circuit and audio-frequency power amplifier.
2. single-board type command amplification board according to claim 1, is characterized in that: described audio-frequency power amplifier adopts many zero potentials circuit.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201010510976.5A CN102457621B (en) | 2010-10-19 | 2010-10-19 | Single-board type command amplification board |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201010510976.5A CN102457621B (en) | 2010-10-19 | 2010-10-19 | Single-board type command amplification board |
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| Publication Number | Publication Date |
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| CN102457621A CN102457621A (en) | 2012-05-16 |
| CN102457621B true CN102457621B (en) | 2014-07-09 |
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN201010510976.5A Expired - Fee Related CN102457621B (en) | 2010-10-19 | 2010-10-19 | Single-board type command amplification board |
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Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2018165918A1 (en) * | 2017-03-15 | 2018-09-20 | 深圳市台电实业有限公司 | Double-backup conference unit and double-backup conference system |
| CN108566495B (en) * | 2018-05-31 | 2023-10-10 | 杭州小犇科技有限公司 | User circuit supporting full calling function |
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|---|---|---|---|---|
| CN2282310Y (en) * | 1995-05-17 | 1998-05-20 | 宋光明 | Program control automatic instructure telephone device |
| CN2342539Y (en) * | 1998-04-09 | 1999-10-06 | 湖南广播设备厂 | Loudspeaker with short circuit and overload protection function |
| CN201336682Y (en) * | 2008-12-25 | 2009-10-28 | 湖南德海通信设备制造有限公司 | Dictating user board |
| CN201830334U (en) * | 2010-10-19 | 2011-05-11 | 长沙常有通信设备有限公司 | Single-plate type instruction amplification plate |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US7590251B2 (en) * | 2003-03-21 | 2009-09-15 | D2Audio Corporation | Clip detection in PWM amplifier |
-
2010
- 2010-10-19 CN CN201010510976.5A patent/CN102457621B/en not_active Expired - Fee Related
Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN2282310Y (en) * | 1995-05-17 | 1998-05-20 | 宋光明 | Program control automatic instructure telephone device |
| CN2342539Y (en) * | 1998-04-09 | 1999-10-06 | 湖南广播设备厂 | Loudspeaker with short circuit and overload protection function |
| CN201336682Y (en) * | 2008-12-25 | 2009-10-28 | 湖南德海通信设备制造有限公司 | Dictating user board |
| CN201830334U (en) * | 2010-10-19 | 2011-05-11 | 长沙常有通信设备有限公司 | Single-plate type instruction amplification plate |
Non-Patent Citations (2)
| Title |
|---|
| 基于AT89C2051的扩音电话机的设计;郭翠娟等;《天津工业大学》;20081231;第27卷(第6期);第65-67页 * |
| 郭翠娟等.基于AT89C2051的扩音电话机的设计.《天津工业大学》.2008,第27卷(第6期),第65-67页. |
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