Physics 2225 Minilab 5: Analog Circuits / Digital Circuits Purpose of This Minilab • Gain some basic experience in reading and building electronic circuits. • Test voltage dividers under load. • Build basic amplifier circuits. • Learn how digital circuits and digital logic work.
Purpose of This Minilab. Gain some basic experience in reading and building electronic circuits. Test voltage dividers under load. Build basic amplifier circuits. Learn how digital circuits and digital logic work. Analog Circuits – The Voltage Divider. - PowerPoint PPT Presentation
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
Physics 2225 Minilab 5: Analog Circuits / Digital Circuits
Purpose of This Minilab
• Gain some basic experience in reading and building electronic circuits.
• Test voltage dividers under load.• Build basic amplifier circuits.• Learn how digital circuits and digital logic work.
Physics 2225 Minilab 5: Analog Circuits / Digital Circuits
Analog Circuits – The Voltage Divider
Suppose you have a fixed voltage power supply (Vin).
To generate a voltage Vout (between 0 and Vin): Build a “voltage divider” using two resistors (R1 and R2).
Vin
Vout
Ground (0V)
R1
R2
Physics 2225 Minilab 5: Analog Circuits / Digital Circuits
The Voltage Divider – How it Works
Vin
Vout
Ground (0V)
R1
R2
The total resistance of the circuit is: Rtotal = R1+R2 (1)
The current from Vin to ground is:
I
)2(0
21 RRVI in
)3(0 2IRVVout
21
2
RRRVV inout
Combining (2) and (3):
Ohm’s law for R2:
Physics 2225 Minilab 5: Analog Circuits / Digital Circuits
The Voltage Divider – How to Choose R1 and R2
Vin
Vout
Ground (0V)
R1
R2
I
21
2
RRRVV inout
Example task: Vin = 5V ………..create Vout = 2V
52
21
2 RRR
Many Possible Solutions:R1 = 3 W R2 = 2 WR1 = 30 W R2 = 20 WR1 = 300 W R2 = 200 WR1 = 3000 W R2 = 2000 W etc.
Physics 2225 Minilab 5: Analog Circuits / Digital Circuits
The Voltage Divider – Which Solution to Choose?
Many Possible Solutions:R1 = 3 W R2 = 2 WR1 = 30 W R2 = 20 WR1 = 300 W R2 = 200 W………………………….R1 = 300 K W R2 = 200 K W etc.
Current I is very large(maybe too large for thepower supply to handle)
Current I is very small(Problem when attachingcircuits with smaller resistances to Vout).
Physics 2225 Minilab 5: Analog Circuits / Digital Circuits
Attaching a Simple Circuit to Voltage Divider
Vin
Vout
R1
R2R3
Choose R1 and R2 such that: R1<<R3
R2<<R3
Otherwise Vout drops much lower and is no longer what you designed it to be.
attached circuit
Physics 2225 Minilab 5: Analog Circuits / Digital Circuits
Voltage Divider on the Bread Board
To 5V(Vin)
To Ground(0V)
VoutR1
R2
Physics 2225 Minilab 5: Analog Circuits / Digital Circuits
Measuring Vout of Voltage Divider
For correct polaritymake sure GNDindicator goes into“COM” input onDMM.
Black clipshould beon ground.
Physics 2225 Minilab 5: Analog Circuits / Digital Circuits
Inverting Amplifier Circuit – How it WorksR4 Negative
feedback loop
Virtual equality: Voltage at “-” input = Voltage at “+” input (V- = 0Volt because V+ = 0Volt)
Current flows around op-amp (and basically none into it, because op-amp hasvery high input resistance)
Current through R3 = Current through R4
+
-R3
Vout
Vin
V+
V-I I
Physics 2225 Minilab 5: Analog Circuits / Digital Circuits
Inverting Amplifier Circuit – How it Works
+
-R3
R4
Vout
Vin
V+
V-I I
Applying Ohm’s Law on R3 :333
0RV
RV
RVVI ininin
Applying Ohm’s Law on R4:444
0RV
RV
RVVI outoutout
43 RV
RV outin
3
4
RR
VV
in
out
Physics 2225 Minilab 5: Analog Circuits / Digital Circuits
Inverting Amplifier Circuit – How it Works
+
-R3
R4
Vout
Vin
V+
V-I I
""3
4 amplifiertheofGainRR
VV
in
out
Example: R4 = 10 kW R3 = 5 kW Gain = - 2 This means: If Vin = 2V then Vout = – 4V
Notice how EASY it is to design an amplifier with a specific gainsimply by choosing the proper ratio of R4 and R3 !!!
Physics 2225 Minilab 5: Analog Circuits / Digital Circuits
Inverting Amplifier Circuit – Amplifying a Signal(just to show you more applications…)
+
-R3
R4
Vout
V+
V-I I
Vin Vout
Sinusoidal input signal Sinusoidal output signal:• Is inverted• Has different amplitude
Physics 2225 Minilab 5: Analog Circuits / Digital Circuits
The Inverting Amplifier Circuit YOU Will Build
+
-R3
R4
Vout
VAR1
R2
5V
Voltage divider from Problem 11
Gain of amplifier circuit:
3
4
RR
VVGin
out
Note: +12V and-12V connectionsfor amplifier not shown in diagram.
Physics 2225 Minilab 5: Analog Circuits / Digital Circuits
Any decimal number can be converted to a binary number and storedelectronically (e.g., in a computer).
1’s and 0’s are often stored as High (5Volt) and Low (0 Volt) voltages.
For example, the number shown above (1001) could be represented by 4 “data lines” that have either high or low voltages.
5V 5V0V 0V
1 0 0 1
Physics 2225 Minilab 5: Analog Circuits / Digital Circuits
Digital Circuits – The Basic Idea
Digital CircuitInput #1
Input #2Output
Digital circuits have one or more “inputs” and one or more “outputs”.
• Inputs are wires or pins to which a given voltage is applied.• Outputs are wires or pins that provide a certain voltage. The value of the output voltage depends on the value of the voltages applied to the inputs.
Never apply a voltage to an output! The output already generates its own voltage. You can “read” that voltage (e.g., with a DMM).
Physics 2225 Minilab 5: Analog Circuits / Digital Circuits
Digital Circuits – The Basic Idea
Digital CircuitInput #1
Input #2Output
Why are they called “digital”? Because we apply only two specific voltages to the inputs and we can only receive one of these two voltages on the output, nothing else.
These two voltages are called “High” and “Low” voltage. They are also called “1” and “0” They can represent a binary number (“digit”).
Digital circuits are some of the basic building blocks in computers.
Physics 2225 Minilab 5: Analog Circuits / Digital Circuits
Digital Circuits – TTL
Digital CircuitInput #1
Input #2Output
“TTL” (Transistor-Transistor Logic) circuits are digital circuitsthat use the following “High” and “Low” voltages:
High = 5 Volts = “1”Low = 0 Volts = “0”
Physics 2225 Minilab 5: Analog Circuits / Digital Circuits
Digital Circuits – Example: The Inverter
InverterInput Output
Inverter has only one input and one output.
How the inverter behaves:If you apply a “high” voltage to the input You get “low” voltage at the output.If you apply a “low” voltage to the input You get “high” voltage at the output.
5V on input 0V on output0V on input 5V on output
“1” on input ”0” on output“0” on input “1” on output
…in other words …
…in other words …
Physics 2225 Minilab 5: Analog Circuits / Digital Circuits
Digital Circuits – The Inverter
Truth Table for Inverter
Input Output
0 11 0
The official symbol
This ring symbolizes“inverting”.
Physics 2225 Minilab 5: Analog Circuits / Digital Circuits
The “AND” Gate – Another Digital Circuit
A
BQ
Truth Table for AND Gate
Input A Input B Output Q = A•B
0 0 01 0 00 1 01 1 1
Physics 2225 Minilab 5: Analog Circuits / Digital Circuits
The “NAND” Gate – Another Digital Circuit
A
BQ
Truth Table for NAND Gate
Input A Input B Output Q = A•B
0 0 11 0 10 0 11 1 0
Just like “AND”gate but additionallyinverted”.
Indicates“invert”
Physics 2225 Minilab 5: Analog Circuits / Digital Circuits
What Good are Digital Circuits?
Digital circuits are basically automated decision makers.
Circuit that rings a bellwhen 5V is applied.
Very simple example: A burglar alarm that rings a bell when a door is open but only when the alarm is actually activated. You can use an “AND” gate.
Circuit that produces5V signal if door is open and 0V when closed.
Circuit that produces 5V when alarm is “ON”, 0V when it is “OFF”.
By combining digital circuits you can build very complicateddecision making machines.
Physics 2225 Minilab 5: Analog Circuits / Digital Circuits
4081 : The AND Gate IC (contains 4 gates)5 Volt
Input A
Input B Output Q
View from the top
A and B could, for example,be connected to SW1 and 2on the bread board.
Output Q could, for example,be connected to the logic indicator(green LED) on the bread board.
Physics 2225 Minilab 5: Analog Circuits / Digital Circuits
Remember: These power point presentationsare available on our website and on Canvas, so you can download them on the computer at your lab table.