A Raspberry Pi Zero (W) can require upwards of 100mA – depending on what it is doing. This may not sound like much at first, but given a standard industrial LiPo cell rated at 2,200mAh, that computer won't even last a day. This makes it all the more important to use the battery's energy sparingly. HATs (Hardware Attached on Top) by PiJuice, which have been around for some time, have the circuitry to help you do this. In this article, we take a look at the PiJuice Zero [1], a pHAT that is optimized for the Raspberry Pi Zero (Figure 1).

Use Cases

But first, let's take a brief look at potential application scenarios for a power management HAT: A Raspberry Pi that is connected to a power outlet but needs to run continuously requires UPS protection (UPS being an uninterruptible power supply). If worst comes to worst, the back-up battery can step in at lightning speed and bridge the gap until the power grid is available again.

A second use case is in normal battery-based operation, for example when the Pi is running far away from civilization. The HAT must supply the board with a stable voltage, even if the battery voltage gradually drops. Ideally, the HAT also measures the charge status and reports it to the Pi. A monitoring program can then shut down the computer in good time, which in turn protects the battery from deep discharge. In both examples, there is also a requirement for sophisticated charging management. Instead of replacing the battery, in the second case a solar panel typically recharges the battery, while the UPS uses the power grid for this task.

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