28128 Parallax Inc, 28128 Datasheet - Page 52

• 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

(1) ADC0831
(1) 100 k potentiometer
(10) Jumper wires, give or take a few
The Potentiometer, a Source of Variable Voltage
There is a reason why the voltage at the wiper terminal of a pot changes when you turn
the knob. The wiper terminal makes the single resistive element in the pot work like two
resistors in series. Figure 3-1 shows two resistors in series. When input voltage is applied
and output voltage is measured as shown in Figure 3-1, the circuit is referred to as a
voltage divider. R
terminals on the pot, and their values change as the pot is adjusted. Since the pot causes
the R
divider.
1
Vinput
and R
=Vdd
Resistor Values: When you know the value of the two resistors in Figure 3-1, you can
predict the output voltage using this equation.
Not surprisingly, it’s called the voltage divider equation, and this technique for scaling down
an input voltage is commonly referred to as using a voltage divider.
V
output
2
to vary, we can call our wiper terminal the output of a variable voltage
=
1
Vdd
Vss
V
and R
input
R
R
1
2
×
2
R
Voutput
1
are the resistances between the wiper and the other two
R
+
2
R
2
Figure 3-1
Voltage Divider Circuit
A Voltage Divider Circuit shows how the wiper
in a potentiometer makes the single resistive
element look like two resistors in series.
Voutput is the voltage measured at the wiper
terminal.