The Switch Bounce

1
The Switch Bounce Phenomemon
ECET 1200
2
Switch Terminology
Types
Mechanisms
Construction
3
Switch Terminology
Types

• Fixed

Mechanisms

• Momentary

Construction
4
Switch Terminology
Types
Mechanisms
Construction
Single-pole Single-throw (SPST)
Poles are Pivots
Throws are the number of possible contacts the
arm can touch
5
Switch Terminology
Types
Single-pole Single-throw (SPST)
Mechanisms
Construction
Single-pole Double-throw (SPDT)
Double-pole Single-throw (DPST)
Double-pole Double-throw (DPDT)
6
Switch Interfacing
Will this work?
NO - Inputs float in open position Can pick up
noise Can damage CMOS
7
Switch Interfacing
Will this work?
VCC
NO - Inputs float during transition
8
Switch Interfacing
Will this work?
YES - open provides high input
VCC
closed provides low input
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Switch Bounce
VCC
Switch Bounce
10
Switch Bounce
VCC
11
Switch Bounce
Reset
VCC
Glitch caused by bounce
Typically 50-100 ms
12
Debouncing a Double Throw Switch
Set
VCC
Transition
Reset
VCC
13
Debouncing a Double Throw Switch
Set
VCC
Transition
Reset
VCC
14
Debouncing a Double Throw Switch
Set
VCC
Transition
Reset
VCC
15
Debouncing a Double Throw Switch
Set
VCC
Transition
Reset
VCC
16
The Switch Bounce Phenomemon
ECET 1200
17
Debouncing a Single Throw Switch
One-Shot
Schmitt Trigger
Pulse gt 100 ms
VCC
One-Shot
Retriggerable or Non-Retriggerable?
18
Debouncing a Single Throw Switch
One-Shot
Schmitt Trigger
VCC
Similar to POR
19
Clock Generators
555 Timer
Schmitt Trigger
Oscillator
20
Clock Generators
555 Timer
The most common low-frequency clock generator
Schmitt Trigger
Advantages
Oscillator

• easily obtainable

• easy setup

• adjustable duty cycle

Disadvantages

• limited frequency ( 100 kHz)

• less stable frequency

• less accurate frequency

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Clock Generators
555 Timer
Schmitt Trigger
Oscillator
22
Clock Generators
555 Timer
Advantages

• easily obtainable

Schmitt Trigger

• easy setup

Oscillator
Disadvantages

• limited frequency

• not for precision applications

• very dependent on technology

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Clock Generators
555 Timer
Prepackaged clock generator requires only power
and ground connections
Schmitt Trigger
Advantages
Oscillator

• easily setup

• very precise frequency

• very stable frequency

Disadvantages

• more expensive

• primarily available ³ 1 MHz

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The Switch Bounce Phenomemon
ECET 1200