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Based on single-chip wireless video doorbell scheme
2012-09-14 16:39:34

 

1 overall design scheme

The system structure is mainly composed of 3 parts: the upper computer system, computer system and communication system. The three parts together to complete the main controller and controller information exchange, to achieve the purpose of building monitoring. The main controller and the controller through the wireless digital transmission module of SRWF data and the transmission of the command. The communication model of one to many communication mode, its overall block diagram as shown in figure 1.

The main controller of the main control chip for the AT89C51, through the keyboard to access the room number, after confirmation, SCM control open video capture chip and the buffer chip to work, and in the setting of the baud rate cases, through the serial communication, composed of a single chip microcomputer to data for digital transmission circuit, digital transmission circuit through the wireless channel data send. From the controller to the main control chip AT89C51 is used by digital transmitting circuit, receiving the master control information and data information, to receive a data classification, if the host to send over the address signal from the controller, read the ringing tone data storage circuit, which issued a ringing tone. Then begin to receive the video signal, and through the LCD display circuit for display, the user can through the button control circuit determines whether or not and master for further conversation.

2 hardware circuit design

2.1 the main controller circuit design

The main controller circuit is composed of a single chip computer AT89C51, keyboard scanning circuit, driver and digital display circuit, a watchdog circuit, a wireless data transmission circuit. Master controller system hardware circuit diagram as shown in figure 2.

Its working process as follows: first, through the keyboard scan circuit to scan the user key information, in order to obtain from the machine address, and key information through the 4 LED display, so that users know you want to access the slave address. The user can through the keyboard on the value-added, impairment, lose weight, confirm the modification of its input value. When the user presses a confirmation key when stored at this time, the host slave address, and open the video chip sampling the video signal, while the slave address by wireless digital transmission chip SRWF sent. The response signal received from the machine and the ready signal after the host, in the setting of the baud rate began to send data. Every 1 frame data from the machine to wait for the reply signal, at the same time for each frame of data sending check frame, in order to ensure the accuracy of data transmission.

2.1.1 keyboard scanning circuit

Keyboard scanning part adopts 4 x 4 keyboard, through the P1 port scan level, to the P1 port of the low 4 bits of a bit is zero, then reads the P1 high 4 level. P1 export low position zero to column is low, if the P1 port 4 monitoring to a zero, then through the ranks of the position can know the key part, in the key exists in the process of the jitter problem, solution methods for hardware coding keyboard and software coding, given the cost consideration and AT89C51 high performance considering the design using software coding mode to realize scanning, keyboard scanning circuit as shown in figure 2.

2.1.2 LED display circuit

LED display circuit using dynamic display display, by 74LS248 BCD decoding chip and 74LS138 decoder. The 74LS248 is designed to save I/O resource, in order to control the more peripheral chip. LED segment selected data by 74LS248 decoding over the section of code selection decision, a selected data generated by 74LS138 decoding. When the work first put the key value is converted to BCD code, send into the P0 port fourth, but the P0 port overall replication will destroy the choice of export data. So it is necessary for P0 export data correction, through or logical operations a selected data into the P0 port fourth bit and fifth bit, then the fixed data to the P0 port, at both a selected data and a selected data. To make the display data does not flash, needs to use the human eye visual persistence, each data showed between the time delay control within 10 ms, such that the display figure was not flash. LED display circuit as shown in figure 2.

2.1.3 video acquisition and data transmission circuit

The video capture circuit consists of CAMERA 0V 7620 chip and IDT7205 composition, using the combination method for video data is quite big, but the working of single chip microcomputer low frequency. If the direct collocation is two can not be normally received. Therefore, increasing the buffer chip IDT7205, which is controlled by the single chip computer of its work to achieve the data quantity and the single chip microcontroller match, only allows the receiver to enable IDT7205. If the monitoring to the video chip VSYN jump, P0.7 will be in the output port 1, thereby to control IDT7205 chip to obtain data from video. The SRWF module in use prior to the wireless channel, interface type, interface rate, interface parameters setting, in the


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