Most portable fitness devices, tablets, and medical equipment require a microcontroller to run through their various functions during operation. Usually you can accomplish this with your favorite controller, but as equipment computing power requirements are getting more intense, is it time to revisit your controller toolbox?
These portable devices typically provide invisible intelligence. This means they require little interaction and are easy to install, yet they provide information and value to the user. Portable fitness and medical equipment essentially need to be low power (or last forever), while processing multiple algorithms and tasks.
From this short description we can start to focus on the important microcontroller specifications. For these applications, I find that the combination of memory power, computing power, clock rate, and active power consumption maps out my challenge, along with considerations of memory size (SRAM).
So, what’s the big deal when it comes to power consumption? It is not just a matter of quickly looking for the power consumption line in the microcontroller’s datasheet. The microcontroller’s power consumption specifications meander through several levels, including memory power, clock rate, active power consumption, and sleep power.
Let’s start with the basics. As you begin your exploration into microcontroller device power, always translate the active device current from mA/MHz to mW/MHz by multiplying the former value by the power-supply voltage value. If vendor A is specifying current with a 3V supply and vendor B specifies with a 1.8V supply, it is very difficult to effectively compare the two parts without converting the consumption numbers from current to power.
In this application space, the portable devices have numerous performance profiles that require vastly different amounts of processing horsepower. The trick is to get the device to complete these computations in the minimum amount of time at the minimum power configuration possible, so you can return to a lower power mode as soon as possible. A simple way to think about this is that a sensor manager needs to wake up occasionally, read the sensor, store the data in SRAM, and go back to sleep (Figure 2).
This application minimizes the time it needs to read that sensor (when the microcontroller core and a serial peripheral are powered) so it can quickly get back to low-power sleep mode (where only the SRAM is being powered).
So stop letting power restrain your portable equipment from doing more. New generations of microcontrollers may replenish your power budget. Look for microcontrollers that minimize both the active-mode power consumption and the backup-mode power consumption, while maintaining all the SRAM you need to effectively implement your product.