Approaching the challenge of battery life

The challenge

Modern smart devices and wireless networks are now offering services that were once considered the preserve of science fiction. However, these advancements in technology can bring their challenges. One of the key concerns is balancing performance and battery usage – it is very easy to be in a position where, despite having the technology, products often suffer from not having enough power.

Users often want lots of features, simple interfaces, small devices, as well as a responsive communications network. The increasing reliance on wireless networks to monitor and control remotely poses some interesting challenges. Wireless sensor network devices typically require a 10–20-year single-cell battery life, whilst also delivering high performance in terms of complexity, protocol and radio range. These demanding expectations often conflict with what is possible, so this article will take a look at what can be done to meet them.

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The resources to meet the challenge

There are many factors involved in designing wireless systems and they all need to be considered when trying to maximise battery life. Some key ones include:

Complexity

It is tempting to design products with plenty of features, but this often leads to complexity in use and a challenge to keep power consumption low. It is always a good idea to work out what the minimum requirements are, see whether they can be met in terms of battery life, and then add more features if there is some margin left.

Utilising the latest components for the appropriate solution

Modern silicon processes and architectures mean that many parts of a wireless system can now offer good, low-power operations and extremely low-power sleep modes. However, this often comes at the cost of sacrificing some features, such as the ability to keep a scheduling clock running accurately to time. These then enable battery energy to be managed very effectively. Microcontrollers, for example, can also provide low voltage operation designed for single-cell batteries, with operating currents in the region of 1mA – 20mA and sleep currents less than a microamp.

For long-battery life applications that need to run on an average current of a few microamps, the key is to sleep deeply for most of the time and wake up occasionally to do what is necessary and do it fast. This includes communications, where, perhaps counterintuitively, the highest data rate possible is usually the best for long battery life.

Battery Technology

Developments in battery technology are driven by advances in interest areas, such as handheld devices and electric vehicles. Despite the increases in battery energy density over the last 40 years, battery technology has developed much less rapidly than other technology areas. Battery technology is still a restriction on many system designs, so other efficiency measures are essential in getting long battery life.

Key approaches to maximising battery life

Here are several design approaches that designers utilise to ensure battery life is extended, without the cost, weight and size of higher capacity batteries:

• Use a duty cycle – save energy whilst maintaining perceived performance levels
• Micro-scheduling – going into sleep mode when otherwise waiting for a response
• Use an interrupt-driven software architecture – polling can waste energy.
• Sleep-mode current – use the deepest levels of sleep mode possible
• Low-power support circuits – try to make these even lower power than the microcontroller sleep current
• Battery choice – some battery chemistries are very well suited to long-life applications, with good capacity, temperature range and low self-discharge

To conclude, if you want to make the most of your product’s battery life, choose low-power devices, use extremely low-power sleep modes and carefully use sleep scheduling.

Wherever you are in the product development cycle, or if you have any further questions as to how wireless communications can help your business, contact us today.