Transcript Chapter 1

Pull-Up & Pull-Down Resistors
The How and Why
Instructor:
Richard T. Vannoy II
[email protected]
[email protected]
Pull-Up & Pull-Down Resistors
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2.
3.
4.
5.
Why are they used/needed?
What are they?
What’s the difference between
pull-up & pull-down?
How do they work?
What size resistor should I use?
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How NOT to connect!!

Switch closed = Good Ground

Switch open = FLOATING!!
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Pull-Up Resistor
Switch open = Good 5 volts
Switch closed = Good Ground
I = V / R
= 5V / 10K
= 0.005A
= 5mA
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Pull-Down Resistor
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What Value for R1??
R1 =
1/10th
of R2
R1
Same
as R2
R1
10
Times
R2
R1
10 KΩ
100
KΩ
1,000
KΩ
R2
100 KΩ
100
KΩ
100 KΩ
Switch 4.54 V
Open
Volts
2.5 V
0.45 V
Switch 0 V
Closed
Volts
0V
0V
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THREE GREAT LINKS
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
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http://www.seattlerobotics.org/encoder/mar97/basics.
html Very Basic Circuits; The Pull-up Resistor is an
excellent article with illustrations.
http://www.sparkfun.com/tutorials/218 SparkFun
article 'Pull-Up Resistors’ goes deeper and shows you
how to determine the size of pull-up resistor to use.
http://arduino.cc/en.Tutorial/DigitalPins Arduino article
'Digital Pins’ gives a good explanation why 'floating'
pins cause problems, and shows how to access the
built-in 20K pull-up resistors in the Arduino series of
boards.
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The
End
Any questions?
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