122-28176 Parallax Inc, 122-28176 Datasheet - Page 95

• Manufacturer Part Number: 122-28176
• Description: GUIDE STUDENT PROCESS CONTROL
• Manufacturer: Parallax Inc

Specifications of 122-28176

• Accessory Type: Manual
• Product: Microcontroller Accessories
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• For Use With/related Products: Propeller Education (PE) Kit
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant, Contains lead / RoHS non-compliant

The IR LED emitter and phototransistor are combined in a single package. The pair are
angled for maximum reflection from a surface at a distance of 0.15 inches (3.8 mm) or
about 1/6 of an inch. This non-contact switch responds to an object passing in front of its
window within the range of detection.
From the study of transistors in Chapter 3, a correct configuration is required for this
switch to be sensed as a digital input.
The IR LED is rated at a maximum current of 40 mA. Given that the IR LED drops
around 1.5 V, this leaves 3.5 V for calculating the size of the resistor needed to limit
current to the IR LED.
A 100 Ω current-limiting resistor will be used. Since the base current (dependent on IR
radiation) and gain are not quantifiable, determining collector current requires some
experimentation.
Parts Required
(1) Resistor – 100 Ω
(2) Resistors – 220 Ω
(1) Resistor – 10 kΩ
(1) Resistor – 100 kΩ
(1) Resistor – 1 MΩ
(1) Opto-Reflective Switch – QRB1114
(1) ADC0831
(1) LED – Red
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The uncommitted collector will require a pull-up.
The collector resistor must be sized such that the output has transitions between
light and dark conditions above and below the BASIC Stamp threshold voltage.
The emitter is connected to ground.
Sufficient base current exists. In this case it would be due to IR LED emissions
reflecting off an object.
R = V/I = (Vdd − V
LED
)/I
LED
= (5.0 V−1.5 V)/40 mA = 87.5 Ω.