Signal Processing - May 2017 - 74

Single-Chip
Microcomputer

JTAG
Test/Debug Port

Battery
Voltage Sense
User
Circuitry Push Buttons

Digitizing
Backlight
Backlit
Barometric
Battery Power
Temp-Humidity Control
16 × 2
Pressure
Supply
Sensor
Circuitry LCD Display Sensor
(a)

(b)

Figure 2. The creating prototypes activity at the 2012 Engineering Summer Camp: (a) the lab session and (b) the final device, a portable battery-powered
temperature, humidity, and barometric pressure-monitoring system. JTAG: Joint Test Action Group.

diode (LED) and a phototransistor. The
LED emits a light toward a surface,
and the phototransistor enables measurement of this light reflected from the
surface. The line is specified with a
black color on a white/light colored surface. When an optical sensor is above
the white surface, a large amount of
light is reflected back to the phototransistor. If, on the other hand, the optical
sensor is directly above the black line,
very little light is reflected back to the
phototransistor. Thus, by using a sensor array on the bottom of the robot,
students determine the position of the
robot with respect to the line by measuring the outputs of all the sensors. The
drive system for our robot consists of
two small dc motors. The shafts of
the motors are coupled to rubber
wheels attached to axles connected to
the main body of the robot. The torque
generated by the motors is transferred to
the wheels to give motion to the robot.
■ Students use an Atmel ATmega8 microcontroller. A control algorithm is
implemented that controls the speed
and direction of the robot. The microcontroller has six analog-to-digital converter channels that are
connected to the outputs of the six
sensors. This allows the microcontroller to determine the position of
74

■

the robot with respect to the line and
control the speed and the direction
of the robot accordingly. Pulsewidth
modulation (PWM) varies the speed
of the dc motors and allows for
varying speed of the motor by
changing the width of successive
pulses sent to the motor. These pulses are fed to the motor through a
simple drive circuit consisting of a
logic-level metal-oxide-semiconductor field-effect transistor and a
diode. The higher the width of the
pulses, the faster the motor rotation
and robot speed and vice versa. The
direction of the robot is controlled
by a differential mechanism whereby the speed of one of the motors is
increased or decreased with respect
to the other to turn the robot in a
particular direction.
The complexity of the path and the
speed with which the robot can follow
it depends upon the control algorithm
implemented in the microcontroller.
Students explore three types of algorithms; in other words, bang-bang
control, proportional control, and proportional-derivative-integral control.
Based on the observed results of the
line following, they tune the control
parameters of these algorithms to
achieve better performance.
IEEE Signal Processing Magazine

May 2017

Creating prototypes
This topic is essentially "Microcomputers 101." Students learn and utilize fundamental microcomputer system design
techniques, resulting in the construction
of a fully working design prototype. The
design is a simple ambient temperature
monitoring system. This two-day activity
has a lecture/laboratory format. A full
design overview is provided, and by the
end of the second day, each student has
constructed, fully tested, and optimized
the system prototype.
■ Each day students spend approximately two hours in lecture, and the
remaining time in the Embedded
Systems Design Laboratory. The lectures present important theoretical
descriptions of the hardware and software utilized for the implementation
of the system. The lab periods are
spent constructing, testing, troubleshooting, and verifying proper system operation of their prototype
[Figure 2(a) shows a lab session of
the activity].
■ Theoretical concepts during the initial
day include discussions about system
block diagram (high level), the system schematic, and fundamental
operations, as well as basic breadboarding concepts. The lab session is
used to give an overview of the

Table of Contents for the Digital Edition of Signal Processing - May 2017