Hello everyone, I am “Da Yi Zong”. Today we are going to talk about low power design techniques, which are key to ensuring the continuous operation of embedded systems. Whether it is a microcontroller (MCU) or a PLC, properly utilizing low power modes can greatly extend the battery life of devices.

What is a low power mode?

First, we need to understand one thing: in most cases, devices do not need to operate at full load continuously. For example, in an access control system, it only needs to briefly activate detection when someone approaches; the rest of the time it can sleep to save power. This is where low power modes come into play.

Low power modes are usually divided into several levels; the lower the power consumption, the longer the wake-up time. Taking microcontrollers as an example, there are generally the following modes:

• Idle Mode: The CPU stops working, but most peripherals continue to operate.
• Sleep Mode: The CPU and most peripherals stop, with only a few modules running.
• Deep Sleep: Only the minimal system is running, with power consumption nearly at 0.

After switching to a low power mode, the device will automatically wake up and resume operation as soon as an appropriate interrupt occurs. This way, it spends most of the time in a low power state, saving energy without affecting normal functionality.

How do MCUs and PLCs achieve low power?

Low Power for MCUs

For microcontrollers, most chips come with various built-in low power modes. We just need to follow the chip manual and use specific instructions to easily enter these modes.

For example, in the STM32 microcontroller, by setting the SLEEPONEXIT bit to 1, when the CPU executes the WFI (Wait for Interrupt) instruction, it will enter sleep mode. Similarly, by setting the PDDS bit to 1, when the CPU executes the WFE (Wait for Event) instruction, it will enter a deeper low power mode.

In addition to the CPU itself, we also need to reasonably control the operating modes of various peripherals. For instance, turning off the ADC when idle to reduce unnecessary sensor sampling; using the RTC (Real-Time Clock) module’s interrupt function to avoid frequent queries for the system time, etc.

When programming for microcontrollers, it is also important to pay attention to code quality to avoid infinite loops that waste system resources.

Low Power for PLCs

Compared to microcontrollers, most industrial PLCs do not support sleep modes, but we can still optimize from both hardware and software perspectives.

On the hardware side, try to purchase low power PLC models, such as compact types. Programming can be used to turn off unnecessary functions, such as analog input/output, high-speed counters, and other modules.

On the software side, we should avoid useless instruction loops, such as reducing unnecessary conditional checks and data transfers. Reasonably scheduling task scan times can allow longer scan cycles for low-priority tasks. Utilizing watchdog functions to switch to low power mode during idle states can also help.

Additionally, good circuit design, such as selecting low power components and optimizing wiring, can also aid in extending PLC battery life.

Experience and Considerations

Although low power design seems simple, there are several common issues to be aware of:

1. Peripheral Wake-up Issues. Some low power modes disable certain peripherals; if the program requires regular read/write operations on these peripherals, it may cause abnormal wake-ups. We need to carefully assess system requirements to avoid this situation.
2. RAM Data Retention. When entering deeper low power modes, the internal RAM of the chip may be reset due to power loss, leading to temporary data loss. Depending on the needs, we may need to back up RAM content before entering low power mode.
3. Power Management. In low power modes, the power management circuit also needs to be adjusted accordingly, such as reducing power frequency or switching to backup batteries.
4. Reliability Issues. Frequent switching between low power states may lead to unexpected crashes or excessively long wake-up delays. We need to continuously monitor updates from chip suppliers to optimize firmware and drivers.
5. Power Consumption Testing. Finally, professional power consumption testing should be conducted to evaluate optimization effects and identify potential power consumption black holes.

Although low power technology involves many details to handle, mastering the key points can greatly benefit battery life extension. I hope that through today’s sharing, everyone has gained a preliminary understanding of low power design. You can try to optimize your current projects and experience the actual effects. See you next time!