Low Power Design for Microcontrollers: Extending Battery Life

In industrial and consumer electronics, an increasing number of devices require battery power. To enable devices to operate longer with limited battery capacity, we need to master low power design techniques for microcontrollers. This article will introduce several commonly used methods to reduce power consumption based on practical applications.

1. Understanding Power Consumption

Power consumption is simply the amount of electricity consumed by the microcontroller during operation. Just like household appliances, a desk lamp may only consume a few watts, while an electric water heater can consume over a thousand watts. The power consumption of a microcontroller mainly comes from:

• CPU computation consumption
• Peripheral operation consumption
• IO port output consumption
• Static consumption from various pull-up resistors

2. Using Sleep Modes

Modern microcontrollers have sleep functions, similar to how humans need to sleep when tired. Taking the STM32 as an example, it has several sleep levels:

• Sleep Mode: CPU stops working while peripherals continue to run
• Stop Mode: CPU and most peripherals stop, RAM is retained
• Standby Mode: Almost all modules stop, with the lowest power consumption

Implementation code example:

c复制

// Enter Sleep Mode
void Enter_Sleep_Mode(void)
{
    // Configure SLEEPDEEP bit
    SCB->SCR &= ~SCB_SCR_SLEEPDEEP_Msk;
    // WFI instruction to enter sleep
    __WFI();
}

// Enter Stop Mode
void Enter_Stop_Mode(void)
{
    // Configure SLEEPDEEP bit
    SCB->SCR |= SCB_SCR_SLEEPDEEP_Msk;
    // Stop mode configuration
    PWR->CR |= PWR_CR_PDDS;
    // WFI instruction to enter stop mode
    __WFI();
}

3. Optimizing Peripheral Usage

Just like we should turn off unused appliances, microcontroller peripherals that are not in use should also be turned off promptly. Common optimization methods include:

• Turn off when done: Disable ADC after sampling
• Turn on as needed: Enable serial port only during transmission
• Reduce clock speed: Use low-speed clock for non-critical tasks

4. Optimizing IO Ports

• Disable pull-ups for unused IO: Each pull-up resistor generates static current
• Set output ports to push-pull instead of open-drain: Reduce conduction loss
• Be aware of leakage: Some sensors may leak current even when not in operation, requiring a switch to completely cut power

5. Practical Application Case

Taking an environmental monitoring device as an example:

1. Measure temperature and humidity every 10 minutes
2. Send data wirelessly after collection
3. Enter deep sleep for the remaining time

Key code:

c复制

while(1)
{
    // 1. Wake up from stop mode
    Wake_Up_From_Stop();
    
    // 2. Initialize sensor
    Init_Sensor();
    
    // 3. Collect data
    Get_Sensor_Data();
    
    // 4. Send data
    Send_Wireless_Data();
    
    // 5. Disable peripherals
    Disable_All_Peripheral();
    
    // 6. Enter stop mode, wake up after 10 minutes
    Enter_Stop_Mode();
}

Considerations

1. Choosing a sleep mode requires balancing response speed and power consumption
2. After waking up, some peripherals need to be reconfigured
3. When using external interrupts, be aware of the effects of pull-up/pull-down resistors
4. During debugging, ensure normal functionality before gradually optimizing power consumption

Troubleshooting Common Issues

1. Unable to wake up after sleep: Check the configuration of the wake-up source
2. Power consumption cannot be reduced: Use a current meter to check power-consuming modules one by one
3. Data loss: Ensure data is saved promptly before entering sleep

Practical Suggestions

First, test basic functionality on a development board, using an oscilloscope or current meter to monitor current changes. After mastering the basic principles, you can try applying them in actual projects, gradually optimizing power consumption. It is recommended to prepare a digital multimeter to measure operating current under different states.

Additional Notes

For the design of battery-powered devices, in addition to the low power design of the microcontroller itself, attention should also be paid to:

• Selecting low-power peripheral components
• Power circuit conversion efficiency
• Battery charge detection and protection
• System stability and reliability

By adopting these low power design techniques, the operating time of battery-powered devices can be increased several times, even reaching years of operational time.