28128 Parallax Inc, 28128 Datasheet - Page 14

• 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

The Potentiometer - A Source of Variable Voltage
The potentiometer (pot) has 3 pins on its underside that get plugged into the Board of
Education. On the topside, it has a knob you can twist to adjust it. In this experiment, we
will use variable resistance to get a variable voltage output. Figure 1-3 shows how the
pins on the underside of the pot from the parts kit correspond to the circuit symbol.
Current/Amp: Current happens when electrons travel from point A to point B. Direct current
is what happens when you give the surplus electrons in the negative terminal of a battery a
pathway to get to the positive terminal. The amp is the measurement of how many electrons
per second are traveling through the pathway.
Resistance/Ohm: Resistance is a property of a material in the pathway the electrons travel
through. The more difficult it is for the electrons to get from one end of the pathway to the
other, the higher the resistance. A resistor is just such a pathway, and its resistance is
measured in ohms ( ).
Ohm's Law: When a resistor is used to provide a pathway between the negative and
positive terminals of a battery, you have an electric circuit with voltage, resistance, and
current. Ohm's Law relates the three quantities as follows:
V = I x R
V is the voltage measured in volts, I is the current measured in amps, and R is the
resistance measured in ohms.
The Other Guys: Ever wonder where the words volt, amp, and ohm come from? They are
all named after some of the people who made significant discoveries about electricity. We
already know who the volt is named for; what about the other guys? The amp, also called
the ampere, is named after 18th century physicist André Marie Ampère. The ohm is named
after 19th century physicist Georg Simon Ohm.
Pot
Figure 1-3
Potentiometer Circuit
Symbol and Component