Datasheet

Page 96· Applied Robotics with the SumoBot
Figure 3-8 Front Left and Right QTI Schematics
Each QTI has four components mounted on its PCB, a 220 Ω resistor, a 470 Ω resistor, a
0.01 µF capacitor, and a QRD1114 reflective object sensor. The way these parts are
connected to the QTI's 3-pin header make it so that you can turn its power on or off by
sending either a high or low signal to its W pin. The actual sensor measurements are
taken through its R pin. For example, to turn the left QTI sensor on, send a high signal to
P10. The left QTI is controlled and monitored through P9. The SumoBot's BASIC
Stamp must set P9 high, waits 1 ms, then uses the
RCTIME command to measure the time
it takes for the voltage to drop to 1.4 V. If this time is small, the QTI senses a white
surface. If this time is long, the QTI senses a black surface.
The QRD1114 contains two components. The device inside it that controls how long the
voltage takes to drop from around 5 V to 1.4 V is called an infrared transistor. The
schematic symbol for the IR transistor is shown in Figure 3-9. While an LED is like a 1
way current valve, a transistor is more like a variable current valve. It's analogous to a
faucet. The more you turn the handle, the more water comes out. With an infrared
transistor, the more infrared light that strikes the base (B) surface, the more current (I) the
transistor allows to pass through its collector (C) and emitter (E).
Figure 3-9
Infrared Transistor