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Transcript
Physics 2225 Minilab 5: Analog Circuits / Digital Circuits Purpose of This Minilab • Gain some basic experience in reading and building electronic circuits. • Learn how digital circuits and digital logic work. • Learn some basic digital to analog interfacing. 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 R1 Vout R2 Ground (0V) Physics 2225 Minilab 5: Analog Circuits / Digital Circuits The Voltage Divider – How it Works The total resistance of the circuit is: Rtotal = R1+R2 The current from Vin to ground is: I Vin I Vin 0 R1 R2 Ohm’s law for R2: Vout 0V R2 I R1 (1) (2) (3) Combining (2) and (3): Vout R2 Ground (0V) Vout Vin R2 R1 R2 Physics 2225 Minilab 5: Analog Circuits / Digital Circuits The Voltage Divider – How to Choose R1 and R2 Vout Vin R2 R1 R2 Example task: Vin = 5V ………..create Vout = 2V R2 2 R1 R2 5 Vin I R1 Vout R2 Ground (0V) Many Possible Solutions: R1 = 3 W R2 = 2 W R1 = 30 W R2 = 20 W R1 = 300 W R2 = 200 W R1 = 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 W R1 = 30 W R2 = 20 W R1 = 300 W R2 = 200 W …………………………. R1 = 300 K W R2 = 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). Physics 2225 Minilab 5: Analog Circuits / Digital Circuits 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 R2 R3 attached circuit For Activity 1 you should choose R1 and R2 to be less than 10kW but not too low. Recommended range: a few few hundred W. Physics 2225 Minilab 5: Analog Circuits / Digital Circuits Voltage Divider on the Bread Board To 5V (Vin) To Ground (0V) R1 Vout R2 Physics 2225 Minilab 5: Analog Circuits / Digital Circuits Measuring Vout of Voltage Divider Black clip should be on ground. For correct polarity make sure GND indicator goes into “COM” input on DMM. Physics 2225 Minilab 5: Analog Circuits / Digital Circuits Inverting Amplifier Circuit – How it Works R4 I I V- Vin Negative feedback loop Vout R3 + V+ 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 Physics 2225 Minilab 5: Analog Circuits / Digital Circuits Inverting Amplifier Circuit – How it Works R4 I I V- Vin Vout R3 + V+ V V V 0 Vin Applying Ohm’s Law on R3 : I in in R3 R3 R3 Applying Ohm’s Law on R4: I V Vout 0 Vout Vout R4 R4 R4 Vin Vout R3 R4 Vout R 4 Vin R3 Physics 2225 Minilab 5: Analog Circuits / Digital Circuits Inverting Amplifier Circuit – How it Works R4 I I V- Vin Vout R3 + V+ Vout R 4 " Gain of the amplifier " Vin R3 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 !!! Physics 2225 Minilab 5: Analog Circuits / Digital Circuits Inverting Amplifier Circuit – Amplifying a Signal (just to show you more applications…) R4 Vin I I V- Vout Vout R3 + V+ 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 5V R1 R4 Vin Note: +12V and -12V connections for amplifier not shown in diagram. - R2 R3 Vout + Gain of amplifier circuit: V R G out 4 Vin R3 Voltage divider from Activity 1 Note: Vin is now the input voltage of the amplifier circuit (don’t confuse this with prior Vin from voltage divider). Physics 2225 Minilab 5: Analog Circuits / Digital Circuits Amplifier is an Integrated Circuit (IC): LF351 1 + 2 3 -12V 4 Notice the semicircular cutout (helps to identify pin number) pin 1 8 + 7 6 +12V 8 pins (connections) 4 on each side Out 5 pin chart for LF351 (view from top) (pins 1, 5, 8 are not used) All pin diagrams are shown in the lab manual. Physics 2225 Minilab 5: Analog Circuits / Digital Circuits Connecting LF351 to Create Amplifier Circuit R4 +12V 5V R1 R3 1 8 2 7 3 6 4 5 R2 -12V Vout Physics 2225 Minilab 5: 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 2225 Minilab 5: 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 2225 Minilab 5: Analog Circuits / Digital Circuits 5 6 Out 4 -12V 3 + + 7 2 - 1 - 8 +12V Connecting +12V and –12V Power to the IC Physics 2225 Minilab 5: Analog Circuits / Digital Circuits Complete Amplifier Circuit Voltage divider R4 R3 Clips attached as shown measure Vin of amplifier circuit. Physics 2225 Minilab 5: 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 2225 Minilab 5: 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 2225 Minilab 5: Analog Circuits / Digital Circuits 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 5V 0V 0 1 0V 5V Physics 2225 Minilab 5: Analog Circuits / Digital Circuits Digital Circuits – The Basic Idea Input #1 Digital Circuit 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). Physics 2225 Minilab 5: Analog Circuits / Digital Circuits Digital Circuits – The Basic Idea Input #1 Digital Circuit 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. Physics 2225 Minilab 5: Analog Circuits / Digital Circuits Digital Circuits – TTL Input #1 Digital Circuit 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” Physics 2225 Minilab 5: Analog Circuits / Digital Circuits Digital Circuits – Example: The Inverter Input Inverter 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. …in other words … 5V on input 0V on output 0V on input 5V on output “1” on input ”0” on output …in other words … “0” on input “1” on output Physics 2225 Minilab 5: Analog Circuits / Digital Circuits Digital Circuits – The Inverter The official symbol This ring symbolizes “inverting”. Truth Table for Inverter Input 0 1 Output 1 0 Physics 2225 Minilab 5: Analog Circuits / Digital Circuits The “AND” Gate – Another Digital Circuit A Q B Truth Table for AND Gate Input A Input B Output Q = A•B 0 1 0 1 0 0 1 1 0 0 0 1 Physics 2225 Minilab 5: Analog Circuits / Digital Circuits 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 1 0 1 0 0 0 1 1 1 1 0 Just like “AND” gate but additionally inverted”. Physics 2225 Minilab 5: Analog Circuits / Digital Circuits 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 produces 5V when alarm is “ON”, 0V when it is “OFF”. Circuit that rings a bell when 5V is applied. By combining digital circuits you can build very complicated decision making machines. Physics 2225 Minilab 5: Analog Circuits / Digital Circuits 4081 : The AND Gate IC (contains 4 gates) 5 Volt View from the top Input A Input B A and B could, for example, be connected to SW1 and 2 on the bread board. Output Q 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 Digital to Analog Converter (DAC) The music on an I-pod or on a CD is stored digitally as lots of binary numbers. To actually create sound when playing the music these binary numbers (digital) must be converted into “analog” voltages (the garden-variety that is not limited to specific “High” and “Low” voltages). Once those analog voltages are generated from the digital data they can then be applied to a loudspeaker. Speaker CD (digital data) DAC Physics 2225 Minilab 5: Analog Circuits / Digital Circuits Building a Basic DAC With an Op-Amp I1 SW1 R 5.6kW I2 SW4 I I SW2 SW3 4 V0 Volt 10kW I3 + 22kW I4 V+ 47kW We know this voltage (virtual equality) I I1 I 2 I 3 I 4 Vout Vout R4 I More current means higher Vout. Physics 2225 Minilab 5: Analog Circuits / Digital Circuits I1 SW1 R 5.6kW I2 SW4 I I SW2 SW3 4 10kW I3 V0 Volt - Vout + 22kW I4 V+ 47kW I I1 I 2 I 3 I 4 If SW1 is “0” I1=0 If SW1 is “1” (5V) I1=5V/5.6kW Similar for I2, I3, I4 Physics 2225 Minilab 5: Analog Circuits / Digital Circuits I1 SW1 R 5.6kW I2 SW4 I I SW2 SW3 4 10kW I3 V0 Volt 22kW I4 + Vout V+ 47kW With SW1….SW4 you can switch on and off I1…..I4. I will become more or less. Vout will become more or less. Physics 2225 Minilab 5: Analog Circuits / Digital Circuits I1 SW1 R 5.6kW I2 SW4 I I SW2 SW3 4 10kW I3 22kW I4 V0 Volt + Vout V+ 47kW Because the 4 resistances are different, the 4 currents (when switched on) will be different. When SW1 is switched on more current is added than when SW2 or SW3 or SW4 is switched on. SW1 has a greater influence on Vout than SW2 (contributes more to I). SW2 has a greater influence on Vout than SW3. Etc.. Physics 2225 Minilab 5: Analog Circuits / Digital Circuits I1 SW1 R 5.6kW I2 SW4 I I SW2 SW3 4 10kW I3 22kW I4 V0 Volt + Vout V+ 47kW The 4 resistances are weighted differently by factors of about 2, 4, and 8 just like digits in binary numbers. If the 4 inputs represent a 4 digit binary number, the output voltage is proportional to the value represented by that binary number. Build the circuit and try it out! Physics 2225 Minilab 5: Analog Circuits / Digital Circuits Remember: These power point presentations are available on our website, so you can download them on the computer at your lab table.