Abstract: This article introduced one kind take the monolithic integrated circuit AT89C51 primarily controller and double sound multi-frequency demoding circuit chip MT8880 as a core, realizes through the telephone channel to domestic electric appliances’ long-distance multi-channel intelligent control system. This system is practical, function nimble diverse, may to carry on by the remotely controlled object condition the inquiry as well as the control, may widely apply in the domestic electric appliances or other place each kind of control device.
Key word: AT89C51; MT8880; APR9600; PSTN; Remote control
Introduction
Along with living standard unceasing enhancement, the people hoped that has one kind of automation, the intellectualized degree high control system to be able to implement the remote control to all domestic electric appliances. This article introduced one kind based on PSTN (Public Switched Telephone Network, the public telephone network) realizes to domestic electric appliances’ remote control, may control many kinds of domestic electric appliances’ switches and each kind of hypothesis anytime and anywhere through the telephone, such as rises the air conditioning to decrease temperature ahead of time, the electric boiler preheating and so on, the application prospect is quite ahead of time widespread.
System composition and principle of work
For the simplified circuit, reduces the cost, to enhance the reliability, this system uses AT89C51 to take the master-control unit, it is one section with MCS51 is completely compatible, and internal bringing has the 4KB Flash memory and 256KB the RAM unit chip, therefore may not probably seperately expand EEPROM and static RAM may realize needs the function. Except that outside master-control unit, but also has the ringing examination and the simulation picks machine the electric circuit, the DTMF demoding circuit, the voice prompt electric circuit, to concentrate the controller, system structure diagram as shown in Figure 1.
When needs to control remotely the domestic electric appliances, dials the corresponding telephone number, the ringing examination electric circuit examination bell class signal, if some people answer the telephone or the ringing number of times are short in 6 times, does not have the influence to program-controlled telephone’s use, when the ringing number of times achieves 6 (number of times to be possible from now on through software willfully hypothesis), the monolithic integrated circuit starts the voice prompt electric circuit to send out the prompt sound, inquired whether to enter the electrical appliances control model, according to “0″ the key otherwise, on-hook withdrawal, according to “1″ the key is, will pick on-hook electric circuit to pick automatically machine enters the control state and will pick machine the signal input to the monolithic integrated circuit, after the monolithic integrated circuit will receive will pick machine the signal, start pronunciationPrompts the electric circuit to send out the prompt sound, prompts the operator to input the password perhaps the withdrawal (system support online revision password). The input password after the DTMF receive, transforms the binary number and with saves beforehand in monolithic integrated circuit’s password compares, if does not tally, then the voice prompt password is wrong, may once more resume load, if three password mistakes, then sends the prompt sound and the automatic on-hook; If the password match case voice prompt selectivity control channel (pressed key 1~8 separately expressed that 1~8th channel, control 8 groups electric appliances separately). After port select, presses down “1″ the key to indicate that opens this group electric appliance, and had the voice prompt “this group electric appliance already to open”, pressed down “0″ the key to indicate that shut off this group electric appliance, had the prompt sound “this group electric appliance already to close”, pressed down “*” the key to be possible on-hook withdrawal. If the overtime automatic on-hook (time may by software hypothesis).
Hardware circuit design
* the ringing examination and the simulation pick machine the electric circuit
Before analyzing this electric circuit, first introduces on the public telephone network line’s signal and the examination method. The public telephone network’s transmission line is two artificial lines, uses the direct-current ring circuit single mode, can simulate the telephone to provide the direct-current feed, the line signal, the voice data, the voice data, the double voice data and so on. Our country stipulated the standard is, usually time on-hook feed voltage generally for - 48V, to user ringing bell class voltage for 75±15V,25Hz the alternating voltage, the substation picks on-hook status is through the electric current make-and-break realizes to the direct-current ring circuit on, when user on-hook free time, directs current the ring circuit separation, the feed current is 0; Otherwise, after the user picks machine, directs current the ring circuit connection, the feed current above 20mA.
When has the line signal from TEL0, the TEL1 input, as shown in Figure 2, on telephone channel 75±15V,25Hz after the alternating voltage passes through bridge-type rectification Q1 and the filter, the line signal enters the electro-optical coupler 817 1, 2 pins, then from 4 foot output pulse signal, pulse input to 74LS123, the 74LS123 function is transforms the small pulse the big square-wave signal and sends in 89C51 monolithic integrated circuit’s T0 pin to carry on the counting, when counts achieves 6 times, the 89C51 T1 pin sends out the high level, causes the triode PNP8550 breakover, thus relay RELAY attracts gathers, completes the simulation to pick machine the movement. Because the voice signal and the double tonic train signaling voltage is lower than the line signal voltage far, therefore this electric circuit cannot have the misoperation.
* DTMF demoding circuit
When the user inputs after telephone’s keyboard the password or presses down the control push-button, these information select the double audio frequency method through the telephone line to send out. DTMF demoding circuit’s leading role are the receive from TEL0, the TEL1 input double sound multi-frequency signal and transform it the binary code, then loses to the monolithic integrated circuit carries on the data processing, then realizes the control function, as shown in Figure 3.
What this electric circuit uses is the MT8880 double sound multi-frequency decoding chip, can realize the double sound multi-frequency signal (DTMF) transmission and the receive. When transmits the DTMF signal, the signal delivers the transmission data register from D0~D3 after the data bus buffer, controls the programmable ranks counter, synthesizes the DTMF signal after the D/A transformation, in the audio frequency arises suddenly opens the door the control and under the logical control function, (the TONE end) sends out from 8 feet. When receives the DTMF signal, after the simulation picks machine, from TEL0, TEL1 enter the double sound multi-frequency signal to enter MT8880 after the coupling insulating transformer coupling the input foot IN-, DTMF signal after to transport put, the dial tone filter, the high frequency group and the low frequency group separate the bandpass filter to deliver the digital algorithm and the code converter carry on the confirmation, translates into the corresponding 4 binary code, stores the receive data register, when the need outputs to the data bus, sends in 89C51 the P1 mouth. The gain which and input foot IN- and the gain select carries between GS to meet feedback resistance R3 which may adjust transports puts, CP is the interrupt request or the telephone signal sound examination out-port, it and the 89C51 INT0 pin are connected.
* voice prompt electric circuit
In order to enable the operator to understand promptly is controlled domestic electric appliances’ information, enables the product to achieve interactive with the intellectualization, this system has used speech chip APR9600 which the available monolithic integrated circuit controls, the monolithic circuit may record and send out 32~60s, when serial control above separable 256 sections, when concurrent control most greatly separable 8 sections. Has many kinds of hand control ways, the partition management to be convenient, when multistage control the electric circuit is simple, the sampling speed and records the playback time adjustable, each single bond to have starts characteristics and so on halt cycle many kinds of functions. When carries on the sound recording using APR9600, the exterior tonic train signaling enters through the microphone input and the line input way, in the transmitter amplifier brings the automatic gain control through the chip, if the signal scope then directly enters the line input end about 100mV, tonic train signaling after internal filter, sampling circuit processing simulates the quantity way to store special-purpose dodges quickly in the memory. When playback in the chip reads the logic circuit from to dodge saves takes out the signal, passes through a low pass filter to deliver in the power amplifier, then impels the exterior loudspeaker playback directly.
The APR9600 recording and sending out control has many kinds of patterns, has provided enormous convenient for the average consumer use, but generally speaking may divide into the serial control and the concurrent control two kind of patterns, by chip MSEL1, MSEL2 and the M8 foot’s establishment realizes.
In this system, APR9600 is established in advance 8 section of concurrent control patterns, namely MSEL1, MSEL2, /M8 are 1 (meet by the hypothesis positive electricity source). Sets at the RE end is the recording condition, presses down /M1 namely to start to record the first section, loosens the key is the stop. Presses down M2 namely to start to record the second section, loosens the key is the stop, so circulates gets down until to record. The corresponding pronunciation section’s broadcast from software triggering, APR9600 SP , feeds back the SP- termination to the telephone line to the receiver, from the user may hear the voice control chip the prompt sound to carry on the corresponding operation.
* 8 group electric appliance controls
May see by the system structure diagram, the Chinese red army soldier electric appliance controls through at89C51 P2 mouth. Control circuit’s execution component uses the relay. When monolithic confidential realizes to the electric appliance the control, sends out the control signal by the P2 mouth and enlarges after the triode actuates 8 relays, thus has controlled 8 group electric appliance’s make-and-breaks.
Software design
For guarantee system’s reliability service, must have the good software to coordinate, moreover must have the friendly man-machine conversation function, in view of the fact that the above requests, this system software part mainly by the master routine, the interrupt subroutine, the time delay subroutine, the prompt sound has the subroutine and so on several big modules to be composed. Program flow diagram as shown in Figure 4.
Concluding remark
Realizes based on PSTN to domestic electric appliances’ remote control and the conventional remote control way, like the radio telecontrol, the wired remote control, infrared and the ultrasonic wave remote control and so on compares, demonstrated certain superiority, cannot carry on the special wiring, does not take the radio frequency resources, has avoided the electromagnetic pollution. At the same time, as a result of the telephone channel regional networkings, may use the existing telephone network fully, therefore the remote control distance may step the provinces and cities, even surmounts the country.
