70009 Parallax Inc, 70009 Datasheet - Page 58

• Manufacturer Part Number: 70009
• Description: BOOK UNDERSTANDING SIGNALS
• Manufacturer: Parallax Inc
• Type: Signal Analysisr

Specifications of 70009

• Style: Book
• Title: Understanding Signals
• Contents: Guide to Generate, View and Measure Wave Forms
• Product: Microcontroller Accessories
• Lead Free Status / RoHS Status: Not applicable / Not applicable
• Other names: 70009PAR

Let’s calculate the time constant for a 220 Ω resistor and a 1µF capacitor.
The time constant is the time it will take for the charge curve of the capacitor to reach
63% of the applied voltage or to fall to 37% of the applied voltage. This may seem odd
until you consider the following images.
Consider the following example: If you applied 5 V to this RC network, it would take 2
ms for the charge curve to reach 63%, or 3.15 V. It will take approximately 5 times the
time constant (10 ms) for the capacitor to charge to 5 V. Provided you allow the capacitor
Where R is in Ωs
Where C is in Farads (1µF would be .000001 F, .1µF would be .0000001 F).
Time Constant is in seconds
Time
Time
Constant
Constant
=
0.00022
=
220
Figure 4-1:
RC network charge curve.
Note that the capacitor charges quickly at
first, then it progressively takes longer and
longer to completely charge.
Figure 4-2:
RC network discharge curve.
Likewise, the capacitor discharges quickly
at first, then it progressively takes longer
and longer to completely discharge.
seconds
x
0.000001
or
.22
ms