130-28176 Parallax Inc, 130-28176 Datasheet - Page 62

• Manufacturer Part Number: 130-28176
• Description: KIT PARTS PROCESS CONTROL
• Manufacturer: Parallax Inc

Specifications of 130-28176

• Accessory Type: Education Kit
• Product: Microcontroller Accessories
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• For Use With/related Products: Board of Education Full Kit
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant, Contains lead / RoHS non-compliant

In the CdS (Cadmium Sulfide) photoresistor, light photons excite electrons and allow
them to flow more freely. This in turn changes the resistance. As light level increases,
resistance decreases. In our case, as we shade the photoresistor, its resistance increases.
A greater voltage is dropped on the bottom half of the voltage divider (from the wiper to
Vss). When the voltage drop to ground increases above the threshold voltage, the BASIC
Stamp senses P8 as a logical HIGH.
√
Cast a shadow over the the photoresistor. What happens to voltage? When does
your light energize?
Figure 3-4
Photoresistor Added
to Potentiometer
Portion of the Circuit