28128 Parallax Inc, 28128 Datasheet - Page 24

• Manufacturer Part Number: 28128
• Description: KIT BASIC ANALOG/DIGI PARTS ONLY
• Manufacturer: Parallax Inc

Specifications of 28128

• Accessory Type: ADC, DAC
• Product: Microcontroller Accessories
• For Use With/related Products: BASIC Stamp® 2 and Board of Education
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Page 14 · Basic Analog and Digital
About the Comparator
Using PBASIC, we programmed the BASIC Stamp to function as a comparator. A
comparator is so named because it's a circuit that compares its input voltage to a
particular voltage, also called the threshold voltage. If the input voltage is higher than the
threshold voltage, the comparator sends a high signal at its output. If the input to the
comparator is below the threshold voltage, it sends a low signal.
In the case of our circuit and program, when the analog voltage at pin P7 is below 1.4
volts, the BASIC Stamp sends a low signal (0 volts) at pin P12. When the analog voltage
at pin P7 is above 1.4 volts a high signal (5 volts) is sent from pin P12. As you can see in
the Debug Terminal, the BASIC Stamp interprets analog input below 1.4 volts as low (0)
and input above 1.4 volts as high (1).
Operating a comparator near the threshold voltage is interesting because you can make a
small change in voltage at a BASIC Stamp input pin, say from 1.3 to 1.5 volts, and it
results in a fairly large change, from 0 to 5 volts at the output.