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FIGURE 2. Arduino Uno development
platform board.
500 mA resettable fuse to guard
against possible damage caused by a
wayward Arduino to the USB ports
on your PC. When plugged into a
USB port, the Arduino takes its power
from it.
• DC power jack ( 2.1 mm, center
positive) for use with an external
power source. Recommended voltage
range is 7-12 volts.
• Low dropout regulators for 5V and
3.3V. The five volt regulator provides
up to 800 mA of current; the 3. 3 volt
regulator provides 50 mA.
Connection pins are provided for
both the 5V and 3.3V regulated
outputs. You can use these pins to
power low current components such
as infrared sensors.
• Indicator LEDs for power, serial transmit, and receive pins,
and digital pin 13 (labeled L).
• Six analog input/output (I/O) pins and 14 digital I/O pins.
The analog pins connect to an internal 10-bit analog-to-digital converter, letting you read voltages from sensors
and other devices. All I/O pins can be used as digital
outputs.
• Power pins to provide external access to the unregulated
and regulated power supplies. For the Beginner Bot, we
only use regulated power.
As with nearly all microcontrollers, you program them
by writing software on your PC, then upload the software
to the Arduino development board. Arduino is no different,
except that it refers to its programs as sketches. Sketches
are written in a programming language very similar to C,
but with some simplifications to aide newcomers. The
Arduino comes with its own integrated development
environment (IDE) software, available as a single download
from the main www.arduino.cc website.
When you upload a compiled sketch to the Arduino, it
is stored in 32K bytes of Flash memory inside the
ATmega328 chip. Programs are stored permanently until
you replace them with another sketch. The Arduino
supports 1K bytes of electrically erasable non-volatile
EEPROM (data survives after power-down) and 2K bytes of
RAM. Data in RAM is volatile; it’s lost when power is
removed from the Arduino.
1. Remove the second deck (from Part 2) from the Beginner
Bot and drill two holes to mount the Arduino. The Uno
board has four mounting holes; pick the ones near the
upper right and bottom left of the board. Center the
board on the deck, leaving a little more space along the
front. Mark the position for the two holes, and carefully
drill using a 1/8” drill bit.
2. Use a pair of 4-40 jackscrews, nuts, and 4-40 x 1/4”
machine screws to mount the Arduino. Jackscrews are
like miniature standoffs, with male threads on one end
and female on the other. If the jackscrews and other
hardware are metal, add plastic washers to prevent a
possible short circuit. The washers may not be needed,
but they’re good insurance.
3. Once the Arduino board has been mounted, you can
attach the prototyping shield (see Part 3 for details)
on top, with the mini (170 tie-point) solderless
breadboard in the middle. You can securely attach the
mini breadboard with self-adhesive foam tape or
Velcro™. For my prototype, I soldered in some extra
header pins front and back to keep the board in
position.
Mounting the Arduino
Part 2 of this series showed how to mount a small
expansion deck to the Beginner Bot so you can easily add
control electronics. The deck has enough space for the
Arduino development board, with room to spare. Check out
Part 3 of the Beginner Bot series for the full construction
details, but here’s a summary.
Use the Right Motors!
The Beginner Bot uses a pair of Tamiya gearboxes that
have been modified according to instructions provided in
Part 2 of this series. Specifically, the motors used in the
gearboxes have been replaced with versions that provide
for operation at six to 12 volts, and with higher efficiency.
These motors are available from Pololu (item #1117),
among other sources. Cost is under $2 each.
Be sure to not use the stock motors that come with
the Tamiya gearboxes. These are rated for only three volts
and can consume copious amounts of current. This
current exceeds the rating of the L298 H-bridge used to
control the motors.
SERVO 11.2011 57
