Transcript Op-amps

Op-Amps
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Purpose
Comparator
Amplifier
• An Op-Amp can be used to either compare two voltages and
see which one is greater, or amplify a given voltage
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Comparator
• An Op-amp can act as a comparator to compare 2 voltages
• It indicates which is bigger by outputting a voltage (0V or 5V)
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Comparator
• The “-” input will act as the baseline
• If the “+” input becomes greater than the “-”, +Vss will come
out the output
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Comparator Lab
• The B input is set at 0.129V
Voltage divider equation
𝑅2
𝑉𝑜𝑢𝑡 = 𝑉𝑖𝑛
𝑅1 + 𝑅2
𝑉𝑜𝑢𝑡
220Ω
= 6𝑉
220Ω + 10,000Ω
𝑉𝑜𝑢𝑡 = 0.129𝑉
• Adjusting the 500Ω
potentiometer raises and
lowers the voltage at A
• When it’s larger an B, an
LED at C will turn on
R1
R2
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•
Each Op-Amp chip contains
Wiring
multiple individual Op-Amps
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Wiring
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Wiring
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Wiring
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Wiring
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LAB
Complete the Op-Amp lab in the book
• Lab: Operational Amplifier (Op-Amp) Comparator
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Amplifier
• In the amplifier setup of the circuit, the Op-Amp amplifies the
Vin and sends it out of Vout
• The setup requires 2 resistors along with the Op-Amp
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Amplifier – How it works
• There are two rules:
• Rule # 1: The voltage at “+”
WILL equal the voltage at “-”
• Rule # 2: No current can enter
an Op-Amp
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Amplifier – How it works
• Suppose 0.0034V is sensed by Vin
• Too little to be sensed by Arduino
• By Rule # 1, VA = VB = 0.0034
A
C
• Voltage drop across R1 = 0.0034V
• By V=IR, I1 = 0.0000034 Amps
• Since no current can enter or exit
the Op-Amp, it all must come
from R2 , I2 = 0.0000034 Amps
• By V=IR, V2 = 3.4 V
B
R2 =1,000,000Ω
I2= 0.0000034 A
R1= 1,000Ω
V1= 0.0034V
I1= 0.0000034 A
D ground
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Amplifier – How it works
• We were able to amplify 0.0034V
to 3.4V
A
C
• That is readable by an Arduino
• We multiplied our input value by
approximately 1000
B
• This is called the “Gain”
• 𝐺𝑎𝑖𝑛 = 1 +
𝑅2
𝑅1
R2 =1,000,000Ω
R1= 1,000Ω
D ground
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LAB
Complete the Op-Amp lab in the book
Lab: Operational Amplifier (Op-Amp) –
Amplifier
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