# Physics 2025 : Analog Circuits / Digital Circuits Purpose of This Minilab Gain some basic experience in reading and building electronic circuits. Test.

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Physics 2025 : 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 2025 : Analog Circuits / Digital Circuits Analog Circuits – The Voltage Divider Suppose you have a fixed voltage power supply (V in ). To generate a voltage V out (between 0 and V in ): Build a voltage divider using two resistors (R 1 and R 2 ). V in V out Ground (0V) R1R1 R2R2

Physics 2025 : Analog Circuits / Digital Circuits The Voltage Divider – How it Works V in V out Ground (0V) R1R1 R2R2 The total resistance of the circuit is: R total = R 1 +R 2 (1) The current from V in to ground is: I Combining (2) and (3): Ohms law for R 2 :

Physics 2025 : Analog Circuits / Digital Circuits The Voltage Divider – How to Choose R 1 and R 2 V in V out Ground (0V) R1R1 R2R2 I Example task: V in = 5V ………..create V out = 2V Many Possible Solutions: R 1 = 3 R 2 = 2 R 1 = 30 R 2 = 20 R 1 = 300 R 2 = 200 R 1 = 3000 R 2 = 2000 etc.

Physics 2025 : Analog Circuits / Digital Circuits The Voltage Divider – Which Solution to Choose? Many Possible Solutions: R 1 = 3 R 2 = 2 R 1 = 30 R 2 = 20 R 1 = 300 R 2 = 200 …………………………. R 1 = 300 K R 2 = 200 K etc. Current I is very large (maybe too large for the power supply to handle) Current I is very small (Problem when attaching circuits with smaller resistances to V out ).

Physics 2025 : Analog Circuits / Digital Circuits Attaching a Simple Circuit to Voltage Divider V in V out R1R1 R2R2 R3R3 Choose R 1 and R 2 such that: R 1 <<R 3 R 2 <<R 3 Otherwise V out drops much lower and is no longer what you designed it to be. attached circuit

Physics 2025 : Analog Circuits / Digital Circuits Voltage Divider on the Bread Board To 5V (V in ) To Ground (0V) V out R1R1 R2R2

Physics 2025 : Analog Circuits / Digital Circuits Measuring V out of Voltage Divider For correct polarity make sure GND indicator goes into COM input on DMM. Black clip should be on ground.

Physics 2025 : Analog Circuits / Digital Circuits Inverting Amplifier Circuit – How it Works R4R4 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 has very high input resistance) Current through R 3 = Current through R 4 + - R3R3 V out V in V+ V- I I

Physics 2025 : Analog Circuits / Digital Circuits Inverting Amplifier Circuit – How it Works + - R3R3 R4R4 V out V in V+ V- I I Applying Ohms Law on R 3 : Applying Ohms Law on R 4 :

Physics 2025 : Analog Circuits / Digital Circuits Inverting Amplifier Circuit – How it Works + - R3R3 R4R4 V out V in V+ V- I I Example: R 4 = 10 k R 3 = 5 k Gain = - 2 This means: If V in = 2V then V out = – 4V Notice how EASY it is to design an amplifier with a specific gain simply by choosing the proper ratio of R 4 and R 3 !!!

Physics 2025 : Analog Circuits / Digital Circuits Inverting Amplifier Circuit – Amplifying a Signal (just to show you more applications…) + - R3R3 R4R4 V out V+ V- I I V in V out Sinusoidal input signal Sinusoidal output signal: Is inverted Has different amplitude

Physics 2025 : Analog Circuits / Digital Circuits The Inverting Amplifier Circuit YOU Will Build + - R3R3 R4R4 V out VAVA R1R1 R2R2 5V Voltage divider from Problem 11 Gain of amplifier circuit: Note: +12V and -12V connections for amplifier not shown in diagram.

Physics 2025 : Analog Circuits / Digital Circuits Amplifier is an Integrated Circuit (IC): LF351 8 pins (connections) 4 on each side Notice the semicircular cutout (helps to identify pin number) pin chart for LF351 (view from top) (pins 1, 5, 8 are not used) -12V pin 1 All pin diagrams are shown in the lab manual. 1 2 3 4 8 7 6 5 - + +12V Out - +

Physics 2025 : Analog Circuits / Digital Circuits Connecting LF351 to Create Amplifier Circuit 1 2 3 4 8 7 6 5 R4R4 +12V -12V R3R3 R1R1 R2R2 5V V out

Physics 2025 : Analog Circuits / Digital Circuits Using the Breadboard for IC connection 5 holes in a column are electrically connected. But: Red and Green are NOT connected across the center break. The center break

Physics 2025 : Analog Circuits / Digital Circuits Inserting IC into Bread Board Insert IC into bread board across the center divide: 4 pins on each side. Push IC all the way down. indentation pin 1 Example: Use any of these 4 holes to connect to pin 4 pin 4

Physics 2025 : Analog Circuits / Digital Circuits Connecting +12V and –12V Power to the IC 1 2 3 4 8 76 5 - + +12V Out - + -12V

Physics 2025 : Analog Circuits / Digital Circuits Complete Amplifier Circuit Voltage divider R3R3 R4R4 Clips attached as shown measure V in of amplifier circuit.

Physics 2025 : Analog Circuits / Digital Circuits Measuring Vout of Amplifier Circuit The output voltage of the amplifier circuit is measured where R4 attaches to pin 6 of the LF351 IC.

Physics 2025 : Analog Circuits / Digital Circuits Taking out an IC Grab the IC with the yellow IC removal tool. Pull evenly and straight upwards. The IC removal tool helps to avoid bent or broken pins.

Physics 2025 : Analog Circuits / Digital Circuits Amplifying an AC Signal R4R4 V out p-p R3R3 A B Function Generator Output Oscilloscope Channel 1 V A p-p - + +12V -12V Oscilloscope Channel 2

Physics 2025 : Analog Circuits / Digital Circuits Amplifying an AC Signal R4R4 V out p-p R3R3 A B Function Generator Output Oscilloscope Channel 1 V A p-p - + +12V -12V Oscilloscope Channel 2

Physics 2025 : Analog Circuits / Digital Circuits Binary Numbers In digital electronics information is coded as binary numbers which contain only Ones and Zeroes. Example: 1001 (binary) = 1x2 3 +0x2 2 +0x2 1 +1x2 0 = 9 (decimal) Any decimal number can be converted to a binary number and stored electronically (e.g., in a computer). 1s and 0s 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 0V 1 0 0 1

Physics 2025 : Analog Circuits / Digital Circuits Digital Circuits – The Basic Idea Digital Circuit Input #1 Input #2 Output 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 2025 : Analog Circuits / Digital Circuits Digital Circuits – The Basic Idea Digital Circuit Input #1 Input #2 Output 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 2025 : Analog Circuits / Digital Circuits Digital Circuits – TTL Digital Circuit Input #1 Input #2 Output TTL (Transistor-Transistor Logic) circuits are digital circuits that use the following High and Low voltages: High = 5 Volts = 1 Low = 0 Volts = 0

Physics 2025 : Analog Circuits / Digital Circuits Digital Circuits – Example: The Inverter Inverter Input 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 output 0V on input 5V on output 1 on input 0 on output 0 on input 1 on output …in other words …

Physics 2025 : Analog Circuits / Digital Circuits Digital Circuits – The Inverter Truth Table for Inverter Input Output 0 1 1 0 The official symbol This ring symbolizes inverting.

Physics 2025 : Analog Circuits / Digital Circuits The AND Gate – Another Digital Circuit A B Q Truth Table for AND Gate Input A Input B Output Q = AB 0 0 0 1 0 0 0 1 0 1 1 1

Physics 2025 : Analog Circuits / Digital Circuits The NAND Gate – Another Digital Circuit A B Q Truth Table for NAND Gate Input A Input B Output Q = AB 0 0 1 1 0 1 0 0 1 1 1 0 Just like AND gate but additionally inverted. Indicates invert

Physics 2025 : Analog Circuits / Digital Circuits What Good are Digital Circuits? Digital circuits are basically automated decision makers. Circuit that rings a bell when 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 produces 5V 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 complicated decision making machines.

Physics 2025 : 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 2 on the bread board. Output Q could, for example, be connected to the logic indicator (green LED) on the bread board.

Physics 2025 : Analog Circuits / Digital Circuits Remember: These power point presentations are available on our website and on Canvas, so you can download them on the computer at your lab table.

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