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Switches
A
A simple on/off switch
B
A
+
5V
-
IF switch is closed
THEN light is on
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B
C
+
5V
-
IF switches A
AND B AND C
are closed THEN
light is on
A
B
+
5V
-
C
EE 1210 - Logic System Design
IF switches A OR
B OR C are
closed THEN
light is on
SwitchLogic-1
A Few Words About Resistors
For our purposes, we can use a very simple model of resistors:
A
Good
Connection
(A wire)
B
A
A
No
Connection
(Open)
B
Poor
Connection
(Resistor)
B
Consider these combinations:
+5V
None
0V
Good wins
over None
0V
C
B
+5V
None
0V
0V
Good
0V
Poor wins
over None
Seattle Pacific University
0V
Poor
Poor
A
+5V
+5V
+5V
+5V
Good
+5V
Good wins
over Poor
EE 1210 - Logic System Design
Don’t do this!
SwitchLogic-2
Controlling Switches
Control
A simple on/off switch with control
A
B
Threshold
If Control is > 2.5V, switch is closed
otherwise, switch is open.
Note: Assume switches are always closed with higher
voltage, open with lower voltage.
Seattle Pacific University
EE 1210 - Logic System Design
SwitchLogic-3
A circuit using switches
5V
5V
Vout=0
Vout
Vin
Vin=5
GND = 0V
Vin
0V
5V
Vout=5
Vin=0
GND = 0V
switch Vout
open
5V
closed 0V
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5V
Inverter
GND = 0V
Vin
EE 1210 - Logic System Design
Vout
SwitchLogic-4
Using Outputs as Inputs
VCC=5V
Vmid
Vout
Vin
0V
5V
Vin
Vmid
Vin
Vin
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Vmid
5V
0V
Vout
0V
5V
Vout
Vout
Buffer
EE 1210 - Logic System Design
SwitchLogic-5
Some more Switch Logic
VCC
Vout
VA
VB
VA
0V
0V
5V
5V
VB
0V
5V
0V
5V
Vout
5V
5V
5V
0V
A
B
C
NAND gate
Vout is 0V only if VA
AND VB are both 5V
A
B
C
A
B
C
AND gate
Seattle Pacific University
EE 1210 - Logic System Design
SwitchLogic-6
Even more Switch Logic
VCC
L = 0V, H = 5V
A
L
L
H
H
C
A
B
B
L
H
L
H
A
B
C
H
L
L
L
C
NOR gate
C is L if A OR B is H
A
B
C
A
B
C
OR gate
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EE 1210 - Logic System Design
SwitchLogic-7