Purpose of This Minilab

1. 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.

2. 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 R1 Vout R2 Ground (0V)

3. Vin R1 Vout R2 Ground (0V) The Voltage Divider – How it Works The total resistance of the circuit is: Rtotal= R1+R2 (1)  The current from Vin to ground is: Ohm’s law for R2: I Combining (2) and (3):

4. Vin R1 Vout R2 Ground (0V) The Voltage Divider – How to Choose R1 and R2 Example task: Vin = 5V ………..create Vout= 2V Many Possible Solutions: R1 = 3 W R2 = 2 W R1 = 30 WR2 = 20 W R1 = 300 WR2 = 200 W R1 = 3000 WR2 = 2000 W etc. I

5. The Voltage Divider – Which Solution to Choose? Many Possible Solutions: R1 = 3 W R2 = 2 W R1 = 30 W R2 = 20 W R1 = 300 WR2 = 200 W …………………………. R1 = 300 K WR2 = 200 K W 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 Vout).

6. Attaching a Simple Circuit to Voltage Divider 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. Vin R1 Vout R3 R2 attached circuit

7. Voltage Divider on the Bread Board To 5V (Vin) To Ground (0V) R2 R1 Vout

8. Measuring Vout of Voltage Divider Black clip should be on ground. For correct polarity make sure GND indicator goes into “COM” input on DMM.

9. I I V- - Vin Vout R3 + V+ Inverting Amplifier Circuit – How it Works R4 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 R3 = Current through R4

10. Inverting Amplifier Circuit – How it Works R4 I I V- - Vin Vout R3 + V+ Applying Ohm’s Law on R3 : Applying Ohm’s Law on R4:

11. Inverting Amplifier Circuit – How it Works R4 I I V- - Vin Vout R3 + V+ 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 gain simply by choosing the proper ratio of R4 and R3 !!!

12. Vin Inverting Amplifier Circuit – Amplifying a Signal(just to show you more applications…) R4 Vout I I V- - Vout R3 + V+ • Sinusoidal output signal: • Is inverted • Has different amplitude Sinusoidal input signal

13. 5V R1 R2 The Inverting Amplifier Circuit YOU Will Build R4 Note: +12V and -12V connections for amplifier not shown in diagram. VA - Vout R3 + Gain of amplifier circuit: Voltage divider from Problem 11

14. 1 8 - - +12V 2 7 Out + + 3 6 4 5 Amplifier is an Integrated Circuit (IC): LF351 Notice the semicircular cutout (helps to identify pin number) pin 1 8 pins (connections) 4 on each side All pin diagrams are shown in the lab manual. -12V pin chart for LF351 (view from top) (pins 1, 5, 8 are not used)

15. 5V R1 R2 Connecting LF351 to Create Amplifier Circuit R4 +12V 1 8 R3 2 7 Vout 3 6 4 5 -12V

16. 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

17. 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. pin 1 indentation Example: Use any of these 4 holes to connect to pin 4 pin 4

18. Connecting +12V and –12V Power to the IC +12V Out 5 6 7 8 - + 2 3 1 4 + - -12V

19. Complete Amplifier Circuit Voltage divider R4 Clips attached as shown measure Vin of amplifier circuit. R3

20. Measuring Vout of Amplifier Circuit The output voltage of the amplifier circuit is measured where R4 attaches to pin 6 of the LF351 IC.

21. 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.

22. - + R4 +12V Oscilloscope Channel 2 Function Generator Output R3 VA p-p Vout p-p A B Oscilloscope Channel 1 -12V Amplifying an AC Signal

23. - + R4 +12V Oscilloscope Channel 2 Function Generator Output R3 VA p-p Vout p-p A B Oscilloscope Channel 1 -12V Amplifying an AC Signal

24. Binary Numbers In digital electronics information is coded as binary numbers which contain only Ones and Zeroes. Example: 1001 (binary) = 1x23+0x22+0x21+1x20 = 9 (decimal) Any decimal number can be converted to a binary number and stored electronically (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. 1 0 0 1 5V 0V 0V 5V

25. Digital Circuits – The Basic Idea Digital Circuit Input #1 Output Input #2 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).

26. Digital Circuits – The Basic Idea Digital Circuit Input #1 Output Input #2 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.

27. Digital Circuits – TTL Digital Circuit Input #1 Output Input #2 “TTL” (Transistor-Transistor Logic) circuits are digital circuits that use the following “High” and “Low” voltages: High = 5 Volts = “1” Low = 0 Volts = “0”

28. Inverter Input Output Digital Circuits – Example: The Inverter 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 …in other words … “1” on input  ”0” on output “0” on input  “1” on output …in other words …

29. Digital Circuits – The Inverter The official symbol This ring symbolizes “inverting”. Truth Table for Inverter Input Output 0 1 1 0

30. The “AND” Gate – Another Digital Circuit A Q B Truth Table for AND Gate Input A Input B Output Q = A•B • 0 0 0 • 0 0 • 0 1 0 • 1 1 1

31. The “NAND” Gate – Another Digital Circuit Indicates “invert” A Q B Truth Table for NAND Gate Input A Input B Output Q = A•B • 0 0 1 • 0 1 • 0 0 1 • 1 1 0 Just like “AND” gate but additionally inverted”.

32. What Good are Digital Circuits? Digital circuits are basically automated decision makers. 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 rings a bell when 5V is applied. 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.

33. 4081 : The AND Gate IC (contains 4 gates) 5 Volt View from the top Input A Input B Output Q 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.

34. 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.