28176 Parallax Inc, 28176 Datasheet - Page 59

• Manufacturer Part Number: 28176
• Description: KIT PARTS PROCESS CONTROL W/TEXT
• Manufacturer: Parallax Inc

Specifications of 28176

• Accessory Type: Process Control
• Product: Microcontroller Accessories
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• For Use With/related Products: BASIC Stamp® 2 and Board of Education
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant, Contains lead / RoHS non-compliant

PROGRAM DISCUSSION
LED
The potentiometer may simply be thought of as a variable voltage divider, such as in
Figure 3-3. Keep in mind that each of these potentiometer voltages, V(a), V(b), V(c), and
V(d), occurs as the knob on the potentiometer is turned to certain positions. Also keep in
mind that each of the voltages can be applied to P8 in Figure 3-1.
The voltage output is a function of the voltage drop to ground across the lower portion of
the potentiometer illustrated by R2 in Figure 3-3. Kirchoff's Voltage Law states that the
“algebraic sum of the voltages in a series circuit must equal the supply voltage.” The
voltage dropped across R1 and R2 must equal the supply voltage, Vdd, of 5 V. Using
Ohm's Law, the circuit may be analyzed:
The total resistance must equal the value of the potentiometer, 10 kΩ.
current flow through the resistor is:
The wiper only changes where it is tapping and splitting the total resistance. The voltage
across R
Figure 3-3 10 kΩ Voltage Divider (Do Not Build)
1
in Figure 3-1 is used to indicate the state of P8: LED On = HIGH.
Current = Voltage / Resistance or I = V/R
I = V/R = 5 V/10 kΩ = 0.5 mA
2
for Figure 3-3b can be found by:
As such, the