27404 Parallax Inc, 27404 Datasheet - Page 112

• Manufacturer Part Number: 27404
• Description: COMPETITION RING FOR SUMOBOT
• Manufacturer: Parallax Inc

Specifications of 27404

• Accessory Type: Hobby and Education
• Product: Microcontroller Accessories
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• For Use With/related Products: SumoBot®
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant, Contains lead / RoHS non-compliant

With some creative programming, you can actually check as many QTIs as you want, and
it will only a fraction of the time that it takes to check just one QTI with the
command when it's detecting black. This activity will show you how.
The Pulse-Decay Trick
Figure 3-14 is a repeat of Figure 3-10, a schematic for what's happening inside the QTIs
after Vdd has been applied to its on/off input, P10.
Below is a routine that calibrates only the left QTI. After turning the device on by setting
P10 high, P9 is also set high, which pushes the value of V
pause, the
amount of time it takes gets stored in the
equal to 1/4 the value of the
The program could next use the
threshold time. If the decay time is greater than the threshold time, the program can
assume the QTI is detecting black. If the decay time is less than the threshold time, the
program can assume the QTI is detecting white.
HIGH 10
HIGH 9
PAUSE 1
RCTIME 9, 1, time
threshold = time / 4
RCTIME
command measures the time it takes for V
time
variable.
RCTIME
time
command and compare the decay time to the
variable. The
0
Figure 3-14
Simplified Version of
the QTI circuit
toward 5 V. After a 1 ms
threshold
0
to decay to 1.4 V. The
variable is set
RCTIME