Tips for accurate estimation of battery life

The second factor that should be kept in mind is the peak current draw from the embedded system. Any battery is rated for a certain number of milliamp hours (mAh) of operation, but when the battery is partially discharged, it is possible that peak current can cause the battery voltage to dip into or below its brown out value. The result will be a dead embedded system long before the battery has truly discharged all of its energy.

Tip no. 6: Compiler vendor tools
Once the battery life analysis has reached the bench testing phase, there are some very exciting compiler-related tools that can be used to verify system assumptions. These tools have the capability to monitor how much energy the system is using at frequencies of 200kHz! What is even better is that they allow the current draw of the system and the code that is being executed to be correlated! An example can be seen in figure 4.

Figure 4: IAR Workbench and I-Scope System Profile. (Click on image to enlarge)

Using such a tool, a developer can then review the profile, determine which tasks or functions are drawing the largest amount of energy from the battery, and focus any low-power optimisations in these areas. There are even tool options that will record how much execution time is spent in which functions, so that the developer can determine which functions and/or tasks are CPU hogs!

Tip no. 7: Get a second opinion
It never hurts—especially when a development cycle or product launch is in jeopardy or critical to the survival of a company—to get a second set of eyes in on the analysis. Whether the person is a coworker or a third party, having another engineer review the estimate and supporting data will result in information and ideas that may not have been considered by the original developer. This greatly helps to ensure that nothing "falls through the cracks" and that—when the product launch day draws near—the members of the design team are confident that the system will not run out of juice before its time. The result is not only a happy boss, but happy users who aren't frustrated by having to recharge their devices partway through the day.

About the author
Jacob Beningo is an embedded systems consultant and lecturer who specialises in the design of resource-constrained and low-energy devices. He works with companies to decrease costs and time to market while maintaining a quality and robust product. He is an avid tweeter, a tip-and-trick guru, a home brew connoisseur, and a fan of pineapple!

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