Abstract: With the rapid development of the electronics industry and the widespread application of portable devices, low-power design has become the mainstream concept in embedded design. This paper, combined with a tobacco curing barn monitor, discusses the design of the monitoring system and the selection of a working circuit controller in three stages. Keywords: Low-power design, tobacco curing barn monitor, component selection, circuit design, software design. In recent years, with the continuous improvement of tobacco production levels in China, the tobacco curing and conditioning process has received increasing attention, becoming a key step in producing high-quality tobacco. However, the traditional method of long-term manual monitoring and data collection using dry and wet bulbs has generated more and more drawbacks and is incompatible with on-site curing barn facilities. Using electronic equipment to monitor the temperature and humidity of the curing barn, reducing manual intervention, has become an inevitable trend in the development of tobacco curing technology. A curing barn monitor can effectively solve the problem of high manpower consumption in tobacco curing. It can monitor the temperature and humidity of the curing barn based on the required temperature and humidity curve for tobacco curing, reducing manual intervention, and has become an inevitable trend in the development of tobacco curing technology. The tobacco curing barn monitoring instrument can effectively solve the problem of high manpower consumption in tobacco curing. It can monitor the temperature and humidity of the curing barn in real time according to the required temperature and humidity curve for tobacco curing, automatically triggering a voice alarm in abnormal situations, and possessing high data accuracy and system stability. Due to the requirements of the application environment, this instrument is positioned as a portable product; therefore, low power consumption and long lifespan become the primary indicators for product promotion. Low power consumption design was a consistent focus throughout the development of this monitoring instrument. This article mainly elaborates on the low power consumption design strategies used in the three stages of embedded system development—component selection, circuit design, and software design. 1. Component Selection Component selection must be considered at the beginning of product development. It is the prerequisite and foundation for achieving low power consumption in the entire product, and it also has the characteristics of being directly related to the product's functional and performance requirements, with strong specificity and targeting. First, the system scheme of the monitoring instrument was formulated. The monitoring instrument mainly consists of a microcontroller, display, voice alarm, real-time clock, external memory, serial port, temperature and humidity data acquisition circuit, keyboard, and power supply. Based on understanding the performance of a large number of similar chips, the selection of components for each part began. The first step is to select a microcontroller as the core control component, as this is a key device determining system performance. There are five main principles for selecting a microcontroller: ① Choose a CMOS device. Since TTL devices consume significantly more power than their corresponding CMOS devices, this is the most direct way to reduce system power consumption. ② It should be able to operate at low frequency and low voltage. The power consumption characteristic of a CMOS circuit is: P = PD + PA, where: P is the total power consumption; PD is the static power consumption, PD = VDD × IDD; PA is the dynamic power consumption, PA = VDD × ITC + V2DD × RfCL. It is evident that the power consumption of a CMOS circuit is mainly dynamic power consumption, which is proportional to the square of the operating frequency and operating voltage. Therefore, while meeting system performance requirements, the operating frequency and voltage should be reduced as much as possible. ③ It should have several switchable operating modes. Many existing microcontrollers have multiple operating modes to reduce power consumption, such as sleep, run, and standby. Using different modes for different operating requirements can reduce unnecessary energy consumption. ④ For specific system functional requirements, select a microcontroller that integrates the corresponding modules, such as LCD driver, A/D sampling, and audio amplifier. These modules should ideally not be implemented using software methods or external circuits, as this can lead to drawbacks such as high power consumption, large errors, and slow debugging. Of course, not every system needs to meet all these principles; performance and power consumption are inherently contradictory, and a choice must be made based on a balanced consideration of both. The microcontroller used in this monitor is the F447 MSP430 series microcontroller from TI. It is a 16-bit CMOS chip with six operating modes, capable of operating at low voltages from 1.8 to 3.6V, and is a microcontroller specifically designed for ultra-low power consumption. In active mode, its current consumption is 280μA; in low-power mode, it is 0.1–1.1μA. A more significant advantage is that it consists of multiple functional modules, each completely independent. Timers, I/O ports, A/D converters, watchdog timers, and LCD drivers can all run independently while the main CPU is in sleep mode and can be woken up by interrupts, thus enabling the system to truly operate at the lowest power consumption. Secondly, selecting peripheral components is also an indispensable step in low-power design. Similar to selecting a microcontroller, the selection of peripheral components should adhere to principles such as low power consumption and high integration. Another important factor is the availability of control pins that can switch between power-off and off states. The voice alarm circuit uses the ISD1420 from ISD Corporation (USA). Besides its excellent voice quality, it features low quiescent current (typical 0.5μA, maximum 2μA) and automatically enters a sustain state immediately after recording and playback (requiring only 0.5μA). Another crucial reason is its integration of a preamplifier, automatic gain control, anti-interference filter, and output amplifier, requiring only a few external circuits during development. This reduces factors that increase power consumption, increases reliability, and improves efficiency. The temperature and humidity sensor used is the STH11 from Sensirion (Switzerland). This sensor integrates two measurements (temperature and humidity), has a wide range, high accuracy, can be submerged in water or heated, and exhibits high sensitivity. Notably, it performs demand-based measurements, requiring only 0.3μA for sustaining when not demanded, making it ideal for low-power design. The real-time clock chosen is the SD2000 series, which operates at a low voltage (3.5V), has a low typical current (1μA), and a built-in disposable battery, allowing for 5 years of use in the event of a power outage. It also incorporates an EEPROM, solving the data storage problem in the monitor. Furthermore, the EEPROM in the SD2000 can be turned on or off via pin settings, achieving power saving. The power supply uses the RT9167 from Richtek, Taiwan, a low-power voltage regulator chip with an operating current of 80μA and a shutdown selection pin. 2. Circuit Design With the selection of suitable components, the circuit design plays a crucial role in maximizing component performance and achieving low power consumption. In summary, the monitor design employed four low-power design strategies. The first is the power supply design. The power supply design reduces system power consumption by shutting down devices or circuits that are in idle or unnecessarily waiting states. Since there are both 3V and 5V voltage options, the monitor is designed with a dual-power module: the voice chip uses a 5V power supply, and other chips use a 3.3V power supply. Considering the transient nature of voice alarms, the voice chip for one RT9176 chip was also disabled, placing it in a zero-power state. Other devices, such as the microcontroller, sensors, and clock, are designed for continuous power supply due to their continuous operation. Additionally, a voltage sampling monitoring signal is implemented to monitor power supply in real time, generating system alarms and data backups based on voltage conditions, enhancing system reliability and usability. Next, the handling of unused pins on various circuit chips is addressed. Third, the handling of chips with chip select pins is crucial. For example, the chip select pin of a real-time clock EEPROM is connected to an I/O pin of the microcontroller, combining the chip select with the read/write signal, ensuring the device is selected only during read/write operations. Finally, the selection of resistors is critical. For input pins requiring pull-up resistors, such as I2C bus data lines, the pull-up resistors are chosen to be as large as possible while still meeting the driving capability, minimizing power consumption on the pull-up resistors. The same approach is taken for other resistors present in the circuit, such as voltage divider resistors in the keyboard. 3. Software Design Low-power software design builds upon low-power hardware design, aiming to minimize system power consumption during operation. Four principles were emphasized in the monitor's design. First, the microcontroller's low-power modes were utilized effectively. Since data acquisition and processing require minimal time, the microcontroller was kept in the deepest possible low-power mode within operational requirements during idle periods. It was woken up every minute by the alarm pin of the real-time clock to perform temperature and humidity measurements, clock readings, LCD refreshes, and data backups. Keyboard input also served as a wake-up interrupt source to handle abnormal situations such as shutdown and parameter settings. Second, as analyzed in the hardware low-power analysis, the lowest possible operating frequency was chosen. The monitor's clock frequency can be reduced to 100kHz, significantly reducing system activity and current consumption. Third, looping, polling, and dynamic scanning methods were avoided during A/D conversion, scanning, and delays, preventing unnecessary power consumption. Hardware resources such as timer interrupts, external interrupts, and module interrupts were utilized effectively. Fourth, the output ports should be pulled high in idle state as much as possible, especially for I/O ports with pull-up resistors, to reduce energy loss through the resistors. 4. Low-Power Design Results The above describes the low-power resources used in the design of this monitor from both hardware and software perspectives. It has reference value for the development of other power-sensitive embedded systems. It can be seen that the selection of resistors is crucial, as it reduces the system current in the mA range; the system frequency and microcontroller operating mode settings are secondary, as they can optimize the system in the hundreds of μA range. Additionally, the power supply strategy for peripheral chips also plays a very important role, but its effect cannot be analyzed solely from the minimum and maximum current. Its function is to prevent the system from performing unnecessary operations in idle states, reducing dynamic power consumption. After optimizing these strategies, the monitor's system current consumption was reduced to 0.58mA for most of the time, about 25% of the original power consumption. Using a single 6Ah battery, it can operate continuously for 10 months, fully meeting application requirements. In practical design experience, I've learned that low-power design requires both top-level analysis to identify major power consumption sources and bottom-level analysis to monitor current consumption at every circuit node and operational stage. Only in this way can we achieve a comprehensive assessment and minimize power consumption.