PROJECTS: TINY WANDERER ROBOT
AVOIDING A FALL
The Tiny Wanderer uses 2 DIY infrared proximity sensors
and a cheap 8-pin microcontroller chip to autonomously
navigate tabletops, obstacle courses, or black-line paths,
depending on the sensor placement and chip programming.
1. Before the robot starts
wandering, the code calibrates
each sensor against the table
surface by measuring the
phototransistor’s output with
the IR LEDs both off and on.
2. As the robot travels, the IR
LEDs blink on and off, and the
code compares the sensed difference in IR bounce-back with the
difference seen during calibration. If there’s no bounce-back —
danger, Tiny Wanderer, danger!
A The robot’s chassis is bolted
together from flat-cut pieces.
B The 2 servomotors each drive
a large wheel with a rubber tire.
C A swiveling caster centered
under the chassis rear provides a third
wheel, for balance.
D The PCB holds an ATtiny85
microcontroller chip, its programming
header, connection headers, a power
switch, and other supporting components. In this project, the ATtiny85 is
programmed in C, with its hexfile firmware generated by the GCC compiler.
H Next to each IR LED is an IR
phototransistor that becomes more
conductive when it sees more infrared.
When a reflective object is close to
the sensor board, the phototransistor
detects IR bounce-back from the LED.
On the PCB, the collectors of the
phototransistors are connected to
VCC through pull-up resistors and to
analog input pins of the microcontroller. This allows the microcontroller
to monitor the IR levels detected. With
this input, it controls the servomotors
according to programmed behavior —
for example, by backing the robot up
when the sensors detect that it’s
about to roll off the table.
3. Face the same 2 sensors
forward, and you can program
the Tiny Wanderer to avoid
obstacles in its path.
E A sensor tray in front of the
chassis holds the 2 sensor arms.
F On the end of each arm is a
I A small piece of unshrunk
heat-shrink tubing blinders the
phototransistor, shielding it from IR
that comes from the LED directly.
G Each sensor board has an
infrared (IR) LED that’s switched
on and off by the microcontroller.
4×AA battery pack supplies
power to the servos and microcontroller.
4. Move the sensors closer
together, facing down, and you
can program the Tiny Wanderer
to follow a black line.
90 Make: makezine.com/29