Pick   want: A wireless data transmission system for pressure sensors is designed by using a wireless transmitting and receiving module combined with single-chip control. The actual debugging shows that the performance meets the design requirements and the transmission distance reaches several tens of meters.
introduction
In today's information age, sensors, which are the functional devices for sensing, collecting, transforming, transmitting and processing various information, have become an indispensable important technical tool in various application fields, especially in automatic monitoring and automatic control systems. In some areas, due to limited conditions, the use of ordinary cable to extract signals is not enough or can not be achieved. In recent years, wireless communication technology has made great progress, especially the advancement of digital circuit and RF circuit technology, making wireless communication more economical and reliable. In this paper, a wireless data acquisition scheme based on pressure sensor is designed by using a dedicated wireless transceiver module.
Overall system design
The system consists of two parts: data acquisition and transmission, and data reception and processing. The data acquisition and transmission part mainly takes the single chip as the core, and also includes the sensor, the signal conditioning circuit, the digital-to-analog conversion circuit and the data transmission module. The data receiving process is to digitally display the received data. The overall system block diagram is shown in Figure 1 .
data collection
The system is mainly collected by Atmel 's AT89C51 single-chip microcomputer as the control processing core, which completes the data acquisition and processing and the wireless transmission of control data. The 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 the MCS-51. . The signal processing circuit mainly uses the instrumentation amplifier AD623 to amplify the weak differential signal collected by the sensor. The AD623 is a low-cost, high-performance instrumentation amplifier of Analog Devices , USA . The digital-to-analog conversion circuit uses the ICL7135 to convert the acquired analog data into digital data. It is a four-and-a-half double-integral A/D converter with high precision, low price and strong anti-interference ability.
The data is sent to the single-chip microcomputer through conditioning and digital-to-analog conversion, and the single-chip computer 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 1 Â System Block Diagram
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Figure 2 Transmitting circuit
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Figure 3 Â Receiving circuit
Wireless data transceiver system
The transceiver system consists of two parts: the transmitting unit ( Fig. 2) and the receiving unit ( Fig. 3) . The working principle is as follows: the single-chip microcomputer outputs 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 , and transmits it through the antenna; the receiving module receives the received signal. Demodulation is performed, and then sent to the decoder PT2272 for decoding, and 4 -bit parallel data is decoded .
The system uses a dedicated transmitting module F05C and a receiving module J04E , which is a low-speed data transmission module designed for wireless transmission of such an encoding circuit. The module is packaged in SMT resin and is small in size. It operates at 315MHz and can be continuously transmitted and received for a long time. The transmitting module F05C uses the sound table resonator to stabilize the frequency, has good frequency consistency and is free of debugging. It is especially suitable for multiple wireless remote control and data transmission systems. It has a wide operating voltage range and low power consumption, 12V is the best working voltage, and the emission current is about 5-8mA . Moreover, the F05C contains an isolation modulation circuit to eliminate the influence of the input signal on the RF circuit . The signal is directly coupled , and the performance stable coded signal can be directly connected to the data input terminal of the F05C . The receiving module J04E adopts a unique super-regeneration circuit structure, which includes amplification and shaping, and the output data signal can be directly sent to the decoder, which is extremely convenient to use, and is a super-regeneration module with good cost performance. , J04E has very low power consumption, current consumption 0.2mA when only 3V, long-term standby state.
The codec PT2262/2272 is a low-power low-cost general-purpose codec circuit manufactured by CMOS technology. The transmitter PT2262 outputs a 12 -bit code, with the upper 8 bits being the address and the lower 4 bits being the data. When transmitting, the 12 -bit code is sent successively in the high order and the low order in the following order , wherein the logical state of the address code is “ 0 â€, “ 1 â€, “floatingâ€, and the logical state of the data code is “ 0 â€, “ 1 †". When the address received by the receiving end PT2272 is the same as the address set by itself, the received data is decoded and output.
The A0~A7 pins of the PT2262 encoder are address pins. Each bit has three logic states: “ 1 â€, “ 0 â€, “floating†Any combination can provide 6561 address codes; D0~D3 pins are data pins, each bit has two states of “ 0 †and “ 1 †; OSC1 and OSC2 are oscillator pins, and an external oscillating resistor can be generated. Oscillation; TE pin is the transmit enable, giving it a low level, it can trigger the oscillator to generate oscillation, the address is encoded together with the input data, and the modulated serial digital signal is output via the DOUT pin, 8 bits. The address code and the 4 -bit data code form a code word, and A0 is the first place. PT2272 is a decoder paired with PT2262 , in which address code A0~A7 must be the same as PT2262 to latch and output the received data; DIN is the data input pin, VT is the valid output decoding valid confirmation output ( usually Low ) , the decoding effectively becomes high. PT2262 emits at least 4 groups of codes each time it is transmitted . After the decoder chip PT2272 receives the signal, the address code is compared and verified by the two times. The VT pin outputs a high level, and the received data D0~D3 locks at the same time. Save and output.
Display circuit
In order to simplify the circuit and reduce the cost, the system uses a dynamic scan driver. The driving of the digital tube includes the bit selection drive and the segment selection drive. The segment selection drive uses the segment selection line control to display different characters, and the bit selection drive uses the bit selection line to control the brightness of a certain position of the display. This system adopts the P1 port low 4 -bit drive 4 -bit BCD latch / decode / driver MC14543 . The output of MC14543 is connected to the seven-segment input of LED to directly drive the digital tube. The bit selection drive is driven by the inverter 74LS04 . Therefore, when the software bit scan is realized by the one-chip computer programming, the digital tube position selection of the common cathode should be inversely assigned. The display process is as follows: (1) The data is sent to the MC14543 , and the digital tube is driven by the decoding; (2) The bit selection signal is sent to the 74LS04 , and a certain bit of the display is turned on after the reverse direction, and the delay is performed. (3) Modify the data pointer to the next character to be displayed and repeat the above process.
Conclusion
This paper introduces a wireless data acquisition and transmission scheme based on pressure sensor. The test shows that the transmission distance reaches several tens of meters, which is suitable for inconvenient connection testing and remote display occasions.
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