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Application scheme of data acquisition system based on IA4420 radio frequency chip and single-chip microcomputer

This article introduces the overall scheme, hardware circuit and software implementation process of a wireless data acquisition system based on IA4420. After reasonable configuration of various parameters, in actual use, all detection indicators meet the relevant technical requirements of national radio management, and have high practical value.

Author: Xu Qian, Wang Jie

This article introduces the overall scheme, hardware circuit and software implementation process of a wireless data acquisition system based on IA4420. After reasonable configuration of various parameters, in actual use, all detection indicators meet the relevant technical requirements of national radio management, and have high practical value.

1 Introduction to IA4420

The IA4420 radio frequency chip is a single-chip, low-power, multi-band FSK transceiver that can work in the four frequency bands of 315/433/868/915 MHz. It integrates all necessary radio frequency functions inside. Only 1 MCU, 1 crystal oscillator and bypass filter capacitor are needed to form a high-reliability transceiver system. It has the characteristics of simple design, low cost, and debugging-free production. Without the need for an external power amplifier, the communication distance can reach more than 200 m.

Figure 1 shows the internal structure of the IA4420. The chip integrates a high-frequency power amplifier (PA), a low-noise amplifier (LNA), an I/Q mixer, a baseband filter, an amplifier, and an I/Q demodulator. In order to facilitate radio frequency design, the IA4420 has a fully integrated phase-locked loop (PLL). The fast phase-locked time feature of the PLL can achieve fast frequency hopping, and its high resolution allows multi-frequency applications in various frequency bands. The programmable baseband bandwidth can be adjusted according to different frequency deviations, data transmission rates and crystal oscillator errors. This transceiver adopts ZZP technology with I/Q demodulation, so no external components (except crystal oscillator and decoupling capacitor) are required in typical applications. In addition, IA4420 integrates data filtering, clock recovery, data pattern recognition, FIFO and transmit data registers. These digital signal processing functions significantly reduce the burden on the controller. In low-power applications, the IA4420 supports low-power operation based on the internal wake-up timer, and the lowest standby current is 0. 3μA.

Application scheme of data acquisition system based on IA4420 radio frequency chip and single-chip microcomputer

2 System design

The structure of the wireless data acquisition system is shown in Figure 2. In the figure, data collection is completed by the corresponding sensor (such as a temperature sensor that monitors the ambient temperature). When the single-chip microcomputer receives the data collection instruction through the IA4420, it will send the data collected by the sensor through the IA4420, and the command end will also receive the data through the IA4420. The IA4420 on the collection side can be programmed with different machine identification codes, so that the command side can control multi-point data collection at the same time.

3 Main hardware design

The hardware core of the wireless data acquisition system is the one-chip computer and IA4420, its main hardware design is shown as in Fig. 3.

Application scheme of data acquisition system based on IA4420 radio frequency chip and single-chip microcomputer

The connection relationship between IA4420 and the one-chip computer is very simple. Pins 1 to 4 are standard SPI interfaces, through which the single-chip microcomputer completes the configuration of the internal registers of the IA4420, as well as sending and receiving FSK data. The fifth pin (nlRQ) of IA4420 is an interrupt request. When the sending register is ready to receive the next byte, or. When the FIFO receives a predetermined number of bits, or encounters a power-on reset, FIFO overflow, etc., the fifth pin will send a low level. Due to the automatic frequency control function (AFC), the IA4420 allows the use of low-precision (low-cost) crystal oscillators. In order to minimize the cost of the system, this chip can provide a clock signal (pin 8) to the microcontroller, thereby avoiding the use of two crystal oscillators.

4 Software design

IA4420 is a highly integrated chip that can flexibly configure various parameters through internal registers. The following describes its main configuration parameter commands (the commands are all 16 bits, and POR is the default value of this command).

4.1 Configuration setting commands

el enables the internal transmit register, e1 must be set to 1 when the data is transmitted through the transmit register mode; ef enables the internal FIFO register, and ef must be set to 1 when the FIFO mode is used to receive and read data. b1 and bO are used to select the working frequency band, as listed in Table 1.

Application scheme of data acquisition system based on IA4420 radio frequency chip and single-chip microcomputer

4.2 Power management commands

er is used to turn on the receiver; ebb is used to turn on the baseband circuit; et is used to turn on the transmitter; es is used to turn on the frequency synthesizer; ex is used to turn on the crystal oscillator; eb is used to turn on the low-voltage detector; ew is used to turn on wake-up Timer; dc is used to disable clock output.

In the transmitting state, et, es, and ex are set to 1; in the receiving state, er, ebb, es, and ex are set to 1.

4.3 Output and FIFO mode commands

f3~f0: used to set the FIF0 interrupt threshold. When the received data bits reach the threshold number, FIFO generates an interrupt.

Al sets the filling condition of FIF0: when al is 0, only after receiving the synchronization word 2DD4h, will it start to write the received data into the FIFO; when a1 is 1, it is always filled.

ff: Enable FIFO filling after receiving synchronous format. Clearing this bit will stop FIFO filling. If you need to restart the synchronization format recognition, you can set this bit to 0 first and then 1.

dr: Disable high-sensitivity reset mode. If this bit is cleared, then a 200 mV disturbance from the power supply will cause the system to reset.

4.4 Transmit configuration control commands

mp and m3~m0 are FSK modulation parameters, and the output FSK frequency can be expressed as:

fout=fo+(-1)SIGN・(M+1)・(15kHz)

Here, f0 is the center frequency of the channel (set by the frequency setting command); M is 4 binary bits m3~m0; SIGN=(mp)XOR (FSK data).

p2~pO are used to set the output power, as listed in Table 2.

Application scheme of data acquisition system based on IA4420 radio frequency chip and single-chip microcomputer

4.5 Frequency setting command

The 12-bit parameter F (f11~f0) is used to set the operating frequency, and its value range is 96~3 903. The output center frequency of the synthesizer is expressed as:

The 1A4420 sending and receiving process is shown in Figure 4 and Figure 5.

Application scheme of data acquisition system based on IA4420 radio frequency chip and single-chip microcomputer

In Figure 4, the transmitter is turned on after initializing the IA4420. When the IA4420 finishes transmitting a byte, it will pull down nIRQ and notify the MCU to write the subsequent bytes to be transmitted. In Figure 5, after the IA4420 parameter configuration is completed, turn on the FIFO receiving mode. After receiving the data, nIRQ will be pulled low to inform the MCU to read the data. After the data packet is received, the FIFO must be reset for subsequent data packet reception.

Concluding remarks

This article introduces the overall scheme, hardware circuit and software implementation process of a wireless data acquisition system based on IA4420. After reasonable configuration of various parameters, in actual use, all detection indicators meet the relevant technical requirements of national radio management, and have high practical value.

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