Pick  want: Using wireless transmitting and receiving module, combined with single-chip control, a wireless data transmission system of pressure sensor is designed. The actual debugging shows that the performance meets the design requirements, and the transmission distance reaches tens of meters.
introduction
In today's information age, sensors, which are functional devices for the perception, collection, conversion, transmission and processing of various information, have become indispensable and important technical tools in various application fields, especially automatic monitoring and automatic control systems. In some fields, due to the limited conditions, the use of ordinary wired cables to extract signals cannot meet the requirements or can not be achieved. In recent years, wireless communication technology has made great progress, especially the advancement of digital circuits and radio frequency circuit technology, making wireless communication more economical and reliable. This article uses a dedicated wireless transceiver module to design a wireless data acquisition program based on a pressure sensor.
System overall design
This system is composed of two parts: data collection and sending, data receiving and processing. The data acquisition and transmission part is mainly based on the single-chip microcomputer, and also includes sensors, signal conditioning circuits, digital-to-analog conversion circuits and data transmission modules. The data receiving process is to digitally display the received data. The overall block diagram of the system is shown in Figure 1 .
data collection
The system acquisition mainly uses AT89C51 microcontroller of Atmel Company as the control processing core, which completes the data acquisition and processing and the wireless transmission of control data. AT89C51 microcontroller is a low-power / low-voltage / high-performance 8 -bit microcontroller with a 4KB programmable/erasable/read-only memory on -chip ; its output pins and command system are compatible with MCS-51 . The signal processing circuit mainly uses the instrumentation amplifier AD623 to amplify the weak differential signal collected by the sensor. AD623 is a low-cost, high-performance instrumentation amplifier of the American ADI Company. The digital-to-analog conversion circuit uses ICL7135 to convert the collected analog data into digital data. It is a four-and-a-half-digit double integral A/D converter, which has the advantages of high accuracy, low price, and strong anti-interference ability.
After conditioning and digital-to-analog conversion, the data is sent to the single-chip microcomputer. The single-chip microcomputer processes the received data, and then sends the pressure data to the digital display circuit to display the data through the wireless transmitting module and the receiving module.
Figure 1Â System Block Diagram
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Picture 2 Transmitting circuit
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Figure 3Â Receiving circuit
Wireless data transceiver system
The transceiver system is composed of a transmitting unit ( Figure 2) and a receiving unit ( Figure 3) . The working principle is: the single-chip microcomputer outputs the 4 -bit parallel data to the encoder PT2262 , and the PT2262 encodes the 4 -bit parallel data, converts it into a serial signal and sends it to the transmitting module F05C , which is transmitted through the antenna; the receiving module will receive the signal It is demodulated and then sent to the decoder PT2272 for decoding to decode 4 -bit parallel data.
This system uses a dedicated transmitting module F05C and a receiving module J04E . This pair of modules is a low-speed digital transmission module designed for wireless transmission of this encoding circuit. The module is packaged in SMT resin and has a small size. It works at 315MHz and can send and receive continuously for a long time. The transmitter module F05C uses an acoustic meter resonator for frequency stabilization, with good frequency consistency, free of debugging, and is especially suitable for multi-transmit and one-receive wireless remote control and data transmission systems. It has a wide operating voltage range and low power consumption. 12V is the best operating voltage, and the emission current is about 5-8mA . Moreover, F05C contains isolation modulation circuit to eliminate the influence of input signal on radio frequency circuit, and the signal is directly coupled with stable performance. The coded signal can be directly connected to the data input terminal of F05C . The receiving module J04E adopts a unique super regenerative circuit structure, which contains amplifying and shaping, and the output data signal can be directly sent to the decoder. It is extremely convenient to use and is a super regenerative module with good cost performance. , J04E has extremely low power consumption, only consumes 0.2mA current at 3V , and can be in standby for a long time.
The codec PT2262/2272 is a low-power and low-cost universal codec circuit manufactured by CMOS technology. The sending end PT2262 outputs a 12 -bit code, the upper 8 bits are the address, and the lower 4 bits are the data. When sending, the 12 -bit codes are sent successively in the order of high bit first and low bit last. The logic state of the address code is " 0 ", " 1 ", "floating", and the logic state of the data code is " 0 ", " 1 " ". When the address received by the receiving end PT2272 is the same as the address set by itself, the received data will be decoded and output.
The A0~A7 pins of the PT2262 encoder are address pins, and each bit has three logic states: " 1 ", " 0 ", and "floating" Any combination can provide 6561 address codes; D0~D3 pins are data pins, and each bit has two states of " 0 " and " 1 " ; OSC1 and OSC2 are oscillator pins, which can be generated by an external oscillator Oscillation; TE pin is the send enable terminal, give it a low level, you can trigger the oscillator to oscillate, the address and the input data are encoded together, and the modulated serial digital signal is output through the DOUT pin, 8 -bit Address code and 4 -bit data code form a code word, A0 is the first bit . PT2272 PT2262 is paired with the decoder, wherein the address code A0 ~ A7 must be provided with the same PT2262 to latch the received data and outputs; to DIN a data input pin, VT is the effective output decoded valid acknowledgment output (often Low ) , the decoding is valid and becomes a high level. PT2262 transmits at least 4 groups of words each time it transmits . After the decoding chip PT2272 receives the signal, its address code is checked twice before the VT pin outputs a high level, and the data received at the same time is locked at D0~D3. Save and export.
Display circuit
In order to simplify the circuit and reduce the cost, this system adopts dynamic scanning drive. The driving of the nixie tube includes bit selection drive and segment selection drive. The segment selection drive uses the segment selection line to control the display of different characters, and the bit selection drive uses the bit selection line to control the brightness of a certain bit of the display. This system uses the low 4 bits of the P1 port to drive the 4 -bit BCD latch / decoder / driver MC14543 . The output of the MC14543 is connected to the seven-segment input of the LED to directly drive the digital tube. The bit selection drive is driven by inverter 74LS04 , so when the software bit scanning is realized by single-chip programming, the bit selection of the common cathode should be inverted assignment. Display process is: (1) the data into the MC14543, after decoding digital drive; (2) into the 74LS04 bit select signal, a reverse drive after a bright display, and delay. (3) Modify the data pointer to the next character to be displayed and repeat the above process.
Concluding remarks
This article introduces a wireless data acquisition and transmission scheme based on pressure sensors. Tests show that the transmission distance reaches tens of meters. It is suitable for inconvenient connection testing and remote display occasions.
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