FIGURE 6. Wheel encoder
mounted on the
RoboProp advanced robot
controller board, available from
my website at http://
• A Propeller with eight 32-
bit 25 MIPS processor cores,
running at 100 MHz.
• 64KB of EEPROM.
• 24 general-purpose I/Os
that can be used for servos or
• Eight 12-bit analog inputs
• Four of the I/Os can be
used for the optional on-board
L298 H-bridge to drive DC
• Four are used for the on-board micro SD card
socket if a µSD card is inserted (up to 32 GB).
Replacing the Board of Education with RoboProp is
• Disconnect all wiring going to the BOE.
bot chassis in such a way that I could pull out the holder
to change batteries without dismounting the controller
board. When fully charged, this gave 11.1VDC which is
dropped to 10.6V by the reverse voltage protection diode
Adding Wheel Encoders
I used the following wiring map:
• Red and black leads from the battery pack to the
screw terminal + and -, respectively.
Since I found it awkward to change the six Ni-MH
batteries from my previous power supply upgrade, I
decided to switch to non-AA batteries. After some
research, I settled on the 18650 Lithium-Ion batteries.
These cells look like somewhat overgrown AA cells, and
provide 3.7V at up to 4,000 mAh, depending on the cells
I took off the two three-cell AA holders and installed
a three-cell 18650 holder beneath the PCB on the metal
Unfortunately, the Boe-Bot does not have wheel
encoders as it ships, so it was not easy to get Robbie to
travel in a straight line.
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