Parallax 28108 User manual
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QTI Line Follower AppKit for the Small Robot (#28108)
Line Following with QTIs
The QTI sensor is a close-proximity infrared emitter and
receiver pair mounted on a tiny PCB. It can be used as
an analog sensor to differentiate between different
levels of infrared reflectivity. It can also be used as a
purely digital device that returns a 1 when it detects a
black line or a 0 if it detects a white background. An
array of four QTI sensors used as digital devices makes
an effective and flexible line-follower for your small
robot.
The QTI positions are adjustable for different sizes and
types of lines. This activity demonstrates how the QTIs
can be used for digital line following on a simple 3/4-
inch wide electrical tape course with a white
background. See the “Downloads and Documentation”
section of the #28108 product page for QTI Line
Follower source code in PBASIC, C, and Arduino.
For this activity, you will need to supply your
own:
Built and tested Boe-Bot, ActivityBot or Arduino
Shield-Bot robot
#2 Philips-head screwdriver
Black ¾-inch electrical tape
White poster board
Kit Contents
Part #
Description
Qty
800-00120
3-wire Extension cable, 12"
4
800-00016
3-inch jumper wires (bag of 10)
2
150-01030
Resistor - 10 kΩ
4
555-27401
QTI sensor
4
451-00303
3-pin male-male header
4
710-00007
7/8-inch screw, pan head, 4-40
4
700-00060
Standoff, round, 1-inch, 4-40
4
713-00007
Spacer, round, 1/2 inch
4
700-00002
3/8-inch screw, pan head, 4-40
4
700-00015
Washer, nylon, #4
4
Copyright © Parallax Inc. QTI LIne Follower AppKit (#28108) v3.0 2/25/2015 Page 1 of 4
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Mounting the QTIs
1. Match the components in your kit to the Kit Contents listed above to make sure all pieces are
present. If anything is missing, contact Parallax Tech Support.
2. Referring to Figure 1, insert the 7/8-inch screws through the top of the small robot chassis, at
the three slots near the front. Two screws will go through the center slot, and one screw each in
the right and left slots.
3. On the underside of the chassis, slip a 1/2-inch unthreaded spacer on each screw, followed by a
1-inch threaded standoff.
4. Attach a QTI sensor to the other end of each threaded standoff, using a 3/8-inch screw. The
sensors should be facing downwards, and the 3-pin headers on each sensor should be pointing
towards the back of the chassis.
5. If necessary, slightly loosen the 7/8-inch screws and adjust the position of the QTI sensors so
that they are closely positioned edge to edge.
6. Tighten all connections securely.
.
Figure 1 – Mechanical Assembly
Building the Sensing Circuits
Each QTI B pin is tied to Vss (Ground/GND) and each W pin is connected to Vdd (5V). R pin connects to
an I/O pin:
•Far right to P4
•Mid right to P5
•Mid left to P6
•Mid right to P7
√Use the schematic (Figure 2) and the wiring diagrams (Figure 3) on the next page to build the
circuits for the three-pin headers. Be sure to use the correct breadboard setup for your specific
robot (Boe-Bot, ActivityBot, or Arduino Shield-Bot). Although there are many ways this circuit can
be built, these setups are simple and thrifty with breadboard real-estate. If you are using a Boe-
Bot with a HomeWork Board (instead of a Board of Education), it won’t interfere with the servo
connections.
Copyright © Parallax Inc. QTI LIne Follower AppKit (#28108) v3.0 2/25/2015 Page 2 of 4
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Figure 2 – Schematic
Use the Figure 4 to connect the servo extension cables to the male-male headers that are plugged into
the breadboard. The other end of each cable is plugged into a QTI. Be careful when you make these
connections, and pay close attention to the wire colors listed in the figure. Notice that the far left and mid
left cables have white wires that plug onto header pins in the same breadboard row. The same applies to
the mid right and far right QTI cables. Instead of common white wires, the mid left and mid right QTI
cables share a pair of black wires.
Boe-Bot
ActivityBot
Shield-Bot
Figure 3 – Wiring Diagrams
Copyright © Parallax Inc. QTI LIne Follower AppKit (#28108) v3.0 2/25/2015 Page 3 of 4
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Use Figure 4 for Boe-Bot, ActivityBot, or Shield-Bot robots. If you set
up your robot’s breadboard according to Figure 2, the servo extension cables
will always be connected in the configuration shown below, regardless of
which robot you are using.
Figure 4 – Servo Extension Cable Connections
What are the 10 kΩresistors for? A 10 kΩ resistor can be added across
each QTI W and R terminal to make the sensor supply an analog output
voltage. This can be useful for systems with analog to digital (A/D) inputs.
IMPORTANT: DO NOT try to use 10 kΩresistors with Parallax line-following
example code; the code will not work.
Revision History
3.0 – PBASIC code removed (archived on #28108 product page); name and images updated to reflect
kit’s compatibility with ActivityBot and Arduino Shield-Bot robots.
2.1 – New information boxes explain the purpose of the (4) 10 kΩresistors included in the QTI Line
Follower AppKit.
Copyright © Parallax Inc. QTI LIne Follower AppKit (#28108) v3.0 2/25/2015 Page 4 of 4
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