Notifications
Clear all
Topic starter
2026-05-08 8:21 am
Introduction
With the development of chip technology and radio frequency (RF) technology, wireless data transmission has become the cornerstone of the modern digital society, which plays an indispensable role from personal mobile communication to industrial Internet of Things. The rapid progress of wireless technology benefits from the coordinated evolution of semiconductor chip technology and RF technology. Chip technology acts as the "brain" for data processing and control, while RF technology serves as the "nerve ending" for information transmission and reception. The in-depth integration of the two keeps evolving toward higher performance, lower power consumption, smaller size and lower cost.
This system is designed to solve the wiring difficulties in engineering construction. It adopts a wireless star networking architecture to collect environmental information within a range of 200 meters. The overall design idea is as follows: wireless sensor nodes collect various data including temperature, humidity, voltage, current, pressure, flow, light intensity, motion state and gas concentration. All collected data is transmitted to the receiver via the wireless network. After receiving the sensor data through the wireless channel, the receiver converts it into serial data and sends it to the background PC for data analysis, processing and visual display.
Low-Power Wireless Node Design
The design of a stable and reliable wireless sensor node belongs to systematic engineering, which requires comprehensive consideration of hardware, software, communication, power supply and other aspects. It integrates four core functions: sensing, processing, communication and power supply. Since low power consumption is a key requirement of this system, the low-power MCU STM32L010F4P6 (purchased from Digikey) is adopted. The nRF24L01p is selected as the radio frequency chip, and the AHT25 temperature and humidity sensor manufactured by Aosong is applied for environmental monitoring.
The low-power MCU STM32L010F4P6 is built around a Cortex-M0+ 32-bit RISC core with a maximum main frequency of 32 MHz. It features ultra-low power consumption and abundant peripheral interfaces.
In run mode, the current consumption is as low as 100 µA/MHz. The low-power run mode consumes approximately 7 µA while maintaining RAM and peripheral functions, enabling fast CPU wake-up. The low-power sleep mode consumes about 4 µA. The stop mode has a typical current of 1.0 µA with RAM content retained, and the typical wake-up time is only 9 µs. The standby mode achieves a typical ultra-low power consumption of 0.3 µA without RAM retention, and the program restarts from reset after wake-up. The VBAT mode consumes around 0.15 µA, which supplies power for the real-time clock and backup registers.
Its on-chip communication peripherals include one I2C, one USART, one SPI and one 12-bit ADC. The timer system consists of one 16-bit advanced control timer, one 16-bit general-purpose timer and one low-power timer. An independent watchdog and a window watchdog are integrated to improve system operational reliability. The internal resource configuration of the MCU is shown in the following figure.
The RF chip adopts nRF24L01p. It is a classic, low-cost and high-performance 2.4 GHz wireless transceiver chip, which is widely applied in the fields of Internet of Things, unmanned aerial vehicles, remote control toys and other scenarios. It features low cost, high integration, ultra-low power consumption and high transmission speed, while it also has some inherent limitations that need attention.
The chip operates in the 2.4 ~ 2.525 GHz ISM frequency band with Gaussian Frequency Shift Keying (GFSK) modulation, providing excellent anti-interference capability. The over-the-air data rate is configurable: 2 Mbps for the highest speed and lowest latency; 1 Mbps is set as the default rate; and 250 kbps is the lowest rate with the longest communication distance, highest receiving sensitivity and strongest anti-interference performance.
The receiving sensitivity reaches -94 dBm at 250 kbps, and approximately -82 dBm at 2 Mbps. The transmit power is programmable with four levels: 0 dBm, -6 dBm, -12 dBm and -18 dBm.
It supports powerful MultiCeiver technology and the Enhanced ShockBurst protocol. Equipped with 6 independent data channels, a single chip can monitor up to 6 different receiving addresses simultaneously, which is highly suitable for one-to-many topology (such as one remote controller for multiple receivers) and many-to-one topology (such as multiple sensor nodes transmitting data to one central receiver).
It supports automatic packet processing, including automatic preamble generation and CRC checksum calculation. Built-in automatic acknowledgment ensures reliable data transmission without intervention from the MCU. Automatic retransmission is also available: if no acknowledgment is received, the chip will retransmit the packet automatically, with configurable retransmission times and delay intervals. This greatly reduces the interrupt burden and software complexity of the main MCU.
The chip achieves excellent low-power performance: the transmit current is about 11 mA @ 0 dBm, the receive current is around 12.5 mA, the standby mode consumes approximately 26 µA, and the power-down mode is less than 1 µA with nearly all modules shut down. It adopts a standard SPI interface for simple connection with the MCU, and comes in a QFN-20 package to save PCB layout space. The minimum system circuit of nRF24L01p is shown in the following figure.
The AHT25 temperature and humidity sensor module produced by Aosong integrates a newly designed dedicated ASIC chip. It features factory calibration, low power consumption, high precision and excellent long-term stability. The module adopts a fully calibrated digital I2C interface with a slave address of 0x38, offering fast response, strong anti-interference capability and high cost performance. It is compatible with 3.3~5.5V main control interfaces and widely used in consumer electronics, automotive electronics, industrial monitoring, meteorological collection and other fields.
The module operates at 3.3～5.5V DC with an operating current lower than 1mA. Its working temperature ranges from -40℃ to +80℃ with a temperature accuracy of ±0.5℃. The humidity measurement range is 0～100%RH with an accuracy of ±3%RH at 25℃. The temperature resolution is 0.01℃ and the humidity resolution is 0.024%RH. The PCB dimension of the module is 22mm×33mm.
Two important performance indicators in node design are power consumption and wireless transmission distance. As the node is designed to be battery-powered, power consumption becomes a critical evaluation metric. To reduce power consumption and extend service life, the ultra-low-power characteristics of STM32L010F4P6, nRF24L01p and AHT25 are fully utilized. The STM32L010F4P6 remains in a low-power sleep state by default, and the following code instruction is used to enter sleep mode in the program.
WDTCONbits.SWDTEN = 1;
Sleep();//进入休眠。
Of course, before the MCU enters sleep mode, both the nRF24L01p and AHT25 must be set to standby mode to reduce peripheral power consumption. The following instructions are used to control them into standby or power-down mode.
SPI_RW_Reg(WRITE_REG + CONFIG ,0x0c);S
SPI_RW_Reg(WRITE_REG + CONFIG ,0x00);//进入掉电。
Another key indicator is the wireless communication distance. Two main factors affect the transmission distance: one is the transmit power at a low data rate on the transmitting side, and the other is the receiving sensitivity on the receiving side (which will be discussed in the receiver section). Although antenna impedance and size also affect the distance, they are not discussed in this paper.
To achieve the maximum transmission distance, the transmit power of the node is set to the maximum level. As mentioned earlier, the maximum output power is 0 dBm, and the communication rate is configured to 250 kbps. The configuration code is shown below.
SPI_RW_Reg(WRITE_REG + EN_AA, 0x00); // 禁止通道自动应答 SPI_RW_Reg(WRITE_REG + SETUP_RETR, 0x03); // 自动重发3次 SPI_RW_Reg(WRITE_REG + RF_SETUP, 0x24); // 数据传输率250Kbps，发射功率0dBm SPI_RW_Reg(WRITE_REG + SETUP_AW, 0x03); SPI_RW_Reg(WRITE_REG + FEATURE, 0x04); SPI_RW_Reg(WRITE_REG + DYNPD, 0x01);
To be continued...............
Yassin | Building Compact, High-Current Connections for Drones & Robots