User Manual

m3pi power nets.
The expansion board’s power comes from the three power rails of the 3pi robot base: VBAT, VBST,
and VCC. VBAT is the battery voltage, which is supplied by the 3pi base’s four AAA cells. VBAT will
change over time as the batteries discharge, and the nominal voltage depends on whether you are
using alkaline or NiMH cells. VBST is the output of a 9.25 V boost regulator supplied by the battery
voltage; this voltage remains constant even as the batteries discharge. VCC is the output of a 5 V
linear voltage regulator supplied by the boosted voltage. All square pads on the expansion PCB are
ground.
The mbed is powered from VBST, the Wixel is powered from VBAT, and the USB A connector gets its
5 V from VCC. The XBee receives its power from the mbed’s 3.3 V VOUT, which means an XBee will
only receive power when an mbed is socketed. If you want to use an XBee without an mbed, you will
need to provide your own 3.3 V power supply for it.
If you want to add your own sensors or custom electronics, you can access these power rails using
the set of 3pi pins near the center of the board (see Section 4.i for more information).
Pololu m3pi User’s Guide © 2001–2017 Pololu Corporation
4. The Expansion Board in Detail Page 30 of 39