28128 Parallax Inc, 28128 Datasheet - Page 161

• 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

Using properties of logarithms, this simplifies to:
Rearranging again gives us an equality in terms of R and C and t:
If R is the unknown value, divide both sides by C. If C is the unknown value, divide both
sides by R. The resulting two equations are useful for determining an unknown R if C is
known, or visa versa.
Try a few different resistor and capacitor combinations from the Analog and Digital Parts
Kit. Remember that capacitor values can vary as much as 20% from their nominal
(named) value. This will in turn cause error in your measured values. However, if a
resistor with a very low tolerance, such as 1% is available, the measurements of
capacitance can be pretty accurate. Once the capacitor has been calibrated, then it's
possible to take accurate resistance measurements with the RC circuit as well
R
R
R
×
=
×
t
C
C
C
=
×
=
ln
ln
ln












t
V
V
V
V
V
V
t
P
P
P
dd
dd
dd
15
15
15












or
C
=
R
×
ln




t
V
V
P
dd
15



