Step 2: Final Assembly
•Start by screwing the Pi-oT 2 Baseboard into
the bottom tray with the 3 provided self-
tapping screws shown in Figure 2.
•Finally, the enclosure lid is ready to be
installed with the 4 long machine screws,
once the Module is programmed and
configured, shown in Figure 3.
Step 3: Battery Choice and UPS Configuration
The Pi-oT 2 features an optional UPS powered by 2 LiFePO4
18650 batteries. The preferred cell for this product is the Lithium
Werks APR18650M1B. The UPS charges the cells to 3.4 Volts at
a maximum charge rate of 1 amp. The UPS will prioritize the
system load over battery charging if the maximum current draw is
reached.
CAUTION: To maximize efficiency, no reverse current protection
is present on the UPS. Use care when installing the LiFePO4
cells.
The UPS communicates to the Raspberry Pi via 2 GPIO
channels:
In the event of power failure, GPIO pin 25 (BCM) will be pulled
Low to signal the UPS is supplying power from the LiFePO4 cells.
The UPS is controlled by GPIO pin 24 (BCM), where logic Low
disables the UPS. This signal is held High when Vin is present,
thus allowing the Module to power on when Vin is initially
supplied.
The configuration of these two signals allows for the following
logic to control the Module-
1. The Raspberry Pi and UPS power on when Vin is first
supplied.
2. The GPIO pin 24 is held high via a python script or
similar.
3. GPIO pin 25 is used as an input to monitor for power
failure.
4. Once GPIO pin 25 is pulled low, the Raspberry Pi can set
a time to wait for power to resume before safely shutting
down.
CAUTION: The UPS will stop delivering power once a
dangerously low voltage level in the cells is detected.
This safety measure should not be used as a backstop
and only as an emergency condition. Please calculate a
reasonable time to run off battery power based on your
individual use case, and battery choice.
5. Once the Raspberry Pi shuts down, the GPIO pin 24 will
go Low, thus removing all power to the system.
6. If power is returned to Vin, the UPS will power on and the
process repeats.
