Anvisningar till Falstads Kretsapplet

Gå till appleten. | Vanliga fel | förberedda kretsar | Skapa och ändra | Spara

Kort introduktion

Detta appletprogram är en elektronisk kretssimulator. När den startar visar den en enkel  LRC krets (om inte länk skrivaren har bestämt en annan start konfiguration). Den gröna färgen betyder positiv spänning. Grå färg betyder noll-potential eller jordad. Rött visar (tyvärr) negativ spänning. De rörliga gula prickarna föreställer konventionell ström (+ till -, ej elektronerna).

Appleten använder datorns CPU mycket intensivt. Det kan vara bra att stanna appleten, genom att bocka i "stopped" om du skall göra andra saker utan att "trögas ner" av en applet som går i bakgrunden.

För att öppna eller sluta en strömbrytare, klicka på det med musen. När musen passerar över en komponent blir den ljusblå och man ser en beskrivning av komponenten och dess tillstånd (till exempel: spänning, ström, effekt) i nedre högra hörnet av fönstret.

Om man högerklickar (eller control-klick med Mac) när musen är över en komponent kan man välja "Edit" (redigera) eller "Delete" (ta bort) för att, till exempel, ändra resistansen på en resistor.

Det kan finnas en till sex grafer i nederkanten av appleten, som fungerar som oscilloskoper. Varje visar spänning (grön) och/eller ström (gul)  över en viss komponent. Eventuellt kan ström kurvan vara gömd bakom spänningskurvan. Högsta (spännings)värdet i oscilloskop fönster visas med text. När musen passerar en osciloskop då blir komponenten som den är kopplad  till färgmarkerad (ljusblå). För att påverka en oscilloskop, högerklicka på den. Stack/Unstack (stappla) innebär att lägga de ovanför/bredvid varandra. Man kan ta bort, ändra svephastighet, välja visade storheter, ändra skala.

För att skapa en oscilloskop som visar en komponent, högerklicka på komponenten och välj View in Scope.

Om simulering går för sakta eller snabbt kan man andra med  Simulation Speed dragreglaget (det har ingen verkan om man inte har tidsberoende komponenter typ kondensatorer, växelspänningskällor eller dylikt). Current speed dragreglaget ändrar hastigheten som gula strömprickarna går med. Power brightness reglerar hur starkt effektförbrukare skall lysa (om du har under Options valt Show power. Show voltage (visa spänning) kan inte väljas samtidigt.

Reset knappen återställer hastigheter till utgångsläget (men tar inte bort ändringar du gjort i kretsen.)

Några vanliga fel

Ingen resistans kopplad till en spänningskälla eller kondensator. Du måste alltid ha NÅGON resistans, annars blir strömmen oändlig. (Kortslutna kondensatorer är tillåtna.)

Singular matrix! betyder att kretsen går inte ihop (2 olika spänningskällor hopkopplade) eller något annat som ger en odefinerad spänning i någon punkt, ev. för att något komponent har okopplade poler.

No konvergens -- en mycket komplicerade krets kan råka ut för att det inte går att beräkna. Eventuellt kan [reset] hjälpa

Förberedda kretsar

Menyn Circuits  kan användas för att vissa mängder av iordningställda kretsar. (Jag har bara hunnit översätta en del!) När du har valt en krets du kan ändra den precis som du vill. Valen som finns:

• Basics (grundläggande kretsar)
• Resistors: en uppsättning olika resistorer kopplade i serie och parallellt.
• Capacitor: Denna visar en kondensator som kan laddas och urladdas genom en strömbrytare
• Inductor: Denna visar en spole som kan bygga upp en magnetfält och visa självinduktans när du växlar en omkoppplare..
• LRC Circuit: Denna visa en svängningskrets med en spole, resistor och kondensator. Du kan sluta strömbrytaren för att få igång ström i spolen och sedan öppna strömbrytaren för att se svängningen.
• Voltage Divider: Denna visar en spänningsdelare som alstrar referensspänningar 7,5V, 5V och 2,5V fårn en 10 spänningskälla.
• Thevenins Theorem Visar nederst en förenklad ersättningskrets to kretsen ovan.
• Nortons Theorem Visar nederst en förenklad ersättningskrets to kretsen ovan.
• A/C Circuits  (växelspänningskretsar)
• Capacitor: en kondensator kopplad till en växelspänningskälla.
• Inductor en spole kopplad till en växelspänningskälla.
• Caps of Various Capacitances: visar hur 3 olika kondensatorer reagera på samma frekvens av växelspänning.
• Caps w/ Various Frequencies: visar hur 3 lika kondensatorer reagera på olika frekvenser av växelspänning.Ju högre frekvens, desto högre ström.
• Inductors of Various Inductances: visar hur 3 olika spolar reagera på samma frekvens av växelspänning.
• Inductors w/ Various Frequencies: visar hur 3 lika spolar reagera på olika frekvenser av växelspänning.Ju lägre frekvens, desto högre ström.
• Impedances of Same Magnitude: shows a capacitor, an inductor, and a resistor that have impedances of equal magnitude (but different phase). The peak current is the same in all three cases.
• Series Resonance: shows three identical LRC circuits being driven by three different frequencies. The middle one is being driven at the resonance frequency (shown in the lower right corner of the screen as "res.f"). The top one is being driven at a slightly lower frequency, and the bottom one has a slightly higher frequency. The peak voltage in the middle circuit is very high because it is resonating with the source.
• Parallel Resonance: these three circuits have the inductor, resistor, and capacitor in parallel instead of series. In this case, the middle circuit is being driven at resonance, which causes the current there to be lower than in the other two cases (because the impedance of the circuit is highest at resonance).
• Passive Filters
• High-Pass Filter (RC). The original signal is shown at the lower left, and the filtered signal (with the low-frequency part removed) is shown to the right. The breakpoint (-3 dB point) is shown at the lower right, as f.3db. The input for this filter consists of two AC sources back-to-back, which adds their voltages together. In real life, you can't do this, but it comes in handy in this applet.
• Low-Pass Filter (RC).
• High-Pass Filter (RL). This high-pass filter uses an inductor rather than a capacitor.
• Low-Pass Filter (RL).
• Band-Pass Filter: this filter passes a range of frequencies close to the resonance frequency (shown at the lower right, as "res.f").
• Notch Filter: Also known as a band-stop filter, this circuit filters out a range of frequencies close to the resonance frequency.
• Twin-T Filter: This filter does a very good job of filtering out 60 Hz signals.
• Other Passive Circuits
• Series/Parallel
1. Inductors in Series. The circuit at left is equivalent to the circuit at right.
2. Inductors in Parallel.
3. Caps in Series.
4. Caps in Parallel.
• Transformers
1. Transformer: A basic transformer circuit with an equal number of windings in each coil.
2. Transformer w/ DC: Here we try to pass a DC current through a transformer.
3. Step-Up Transformer: Here we step 10 V up to 100 V.
4. Step-Down Transformer: Here we step 120 V down to 12 V.
• 3-Way Light Switches: shows how a light bulb can be turned on and off from two locations.
• 3- and 4-Way Light Switches: shows how a light bulb can be turned on and off from three locations.
• Differentiator: shows how a capacitor can act as a differentiator, reflecting changes in voltage.
• Wheatstone Bridge: shows a balanced Wheatstone bridge. If the bridge were not balanced, current would be flowing across from one leg to the other.
• Critically Damped LRC.
• Current Source: shows a source that keeps the current through the circuit constant regardless of the switch positions.
• Inductive Kickback: In this circuit, we have a switch that controls the supply of current to an inductor. An inductor resists any changes in current. If you open the switch, the inductor tries to maintain the same current; it does this by charging the capacitance between the contacts of the switch. (Any two wires in close proximity have some parasitic capacitance between them.) There is a small capacitor (much larger than the actual value) across the switch terminals to simulate this. When you open the switch, the voltage goes very high; in real life, this would cause arcing.
• Blocking Inductive Kickback: shows how inductive kickback can be blocked with a “snubber” circuit.
  
  
• Power Factor: This circuit shows an inductor being driven by an AC voltage. The colors indicate power consumption; red means that a component is consuming power, and green means that the component is contributing power. The left side of the circuit represents the power companys side, and the right side represents a factory (with a large induction motor).
  
  The highly inductive load is causing the power company to work a lot harder than normal for a given amount of power delivered. The graph on the left indicates the power lost in the power companys equipment (the resistor at top left). The graph in the middle is the power delivered to the factory. The graph on the right is the power delivered to the inductor (and then returned, causing the time average of power delivered to be zero).
  
  Even though a peak power of 40 mW is being delivered to the factory, 200 mW is being dissipated in the power companys wires. This is why power companies charge extra for inductive loads.
  
  
• Power Factor Correction: Here a capacitor has been added to the circuit, causing far less energy to be wasted in the power company’s wires (aside from an initial spike to charge the capacitor).
• Resistor Grid: shows current flowing in a two-dimensional grid of resistors.
• Resistor Grid 2.
• Coupled LC's
1. LC Modes(2): Shows both modes of two coupled LC circuits.
2. Weak Coupling.
3. LC Modes(3): Shows all 3 modes of 3 coupled LC circuits.
4. LC Ladder: This circuit is a simple model of a transmission line. A pulse propagates down the length of the ladder like a wave. The resistor at the end has a value equal to the characteristic impedance of the ladder (determined by the ratio of L to C), which causes the wave to be absorbed. A larger resistance or an open circuit will cause the wave to be reflected; a smaller resistance or a short will cause the wave to be reflected negatively. See the Feynman Lectures 22-6, 7.
• Phase-Sequence Network: This circuit generates a series of sine waves with a phase difference of 90°.
• Diodes
• Half-Wave Rectifier: This circuit removes the negative part of an input waveform.
• Full-Wave Rectifier: This circuit replaces a waveform with its absolute value.
• Full-Wave Rectifier w/ Filter: This circuit smoothes out the rectified waveform, doing a pretty good job of converting AC to DC.
• Diode I/V Curve: This demonstrates the response of a diode to an applied voltage. The voltage source generates a sawtooth wave, which starts out at –800 mV and slowly rises to 800 mV, and then immediately drops back down again.
• Diode Limiter.
• DC Restoration. This takes an AC signal and adds a DC offset, making it a positive signal.
• Blocking Inductive Kickback: shows how inductive kickback can be blocked with a diode.
• Spike Generator.
• Voltage Multipliers
1. Voltage Doubler: Doubles the voltage in the AC input signal (minus two diode drops), and turns it into DC.
2. Voltage Doubler 2
3. Voltage Tripler
4. Voltage Quadrupler
• AM Detector: This is a “crystal radio”, an AM radio receiver with no amplifier. The raw antenna feed is shown in the first scope slot in the lower left. The inductor and the capacitor C1 are tuned to 3 kHz, the frequency shown in the lower right as “res.f”. This picks up the carrier wave shown in the middle scope slot. A diode is used to rectify this, and the C2 capacitor smoothes it out to generate the audio signal in the last scope slot (which is simply a 12 Hz sine wave in this example). By experimenting with the value of C1’s capacitance, you can pick up two other “stations” at 2.71 kHz and 2.43 kHz.
• Triangle-to-Sine Converter
• Transistors
• Switch.
• Emitter Follower.
• Astable Multivibrator: A simple oscillator. The applet has trouble simulating this circuit, so there might be a slight delay every time one of the transistors switches on.
• Bistable Multivibrator (Flip Flop): This circuit has two states; use the set/reset switches to toggle between them.
• Monostable Multivibrator (One-Shot): When you hit the switch, the output will go to 1.7 V for a short time, and then drop back down.
• Common-Emitter Amplifier: This circuit amplifies the voltage of the input signal by about 10 times.
• Unity-Gain Phase Splitter: Outputs two signals 180° out of phase from each other.
• Schmitt Trigger.
• Current Source: The current is the same regardless of the switch position.
• Current Source Ramp: Uses a current source to generate a ramp waveform every time you hit the switch.
• Current Mirror: The current on the right is the same as the current on the left, regardless of the position of the right switch.
• Differential Amplifiers
1. Differential Input: This circuit subtracts the first signal from the second and amplifies it.
2. Common-Mode Input: This shows a differential amplifier with two equal inputs. The output should be a constant value, but instead the input waveforms make it through to the output (attenuated rather than amplified). (When both inputs change together, that is called “common-mode input”; the “common-mode rejection ratio” is the ability of a differential amplifier to ignore common-mode signals and amplify only the difference between the inputs.)
3. Common-Mode w/Current Source: This is an improved differential amplifier that uses a current source as a load. The common-mode rejection ratio is very good; the circuit amplifies the small differences between the two inputs, and ignores the common-mode signal.
• Push-Pull Follower: This is another type of emitter follower.
• Oscillators
1. Colpitts Oscillator
2. Hartley Oscillator
3. Emitter-Coupled LC Oscillator
• JFETs
• JFET Current Source
• JFET Follower: This is like an emitter follower, except that the output is 3V more positive than the input.
• JFET Follower w/zero offset
• Common-Source Amplifier
• Volume Control: Here the JFET is used like a variable resistor.
• MOSFETs
• CMOS Inverter: The white “H” is a logic input. Click on it to toggle its state. “H” means “high” (5 V) and “L” means “low” (0 V). The output of the inverter is shown at right, and is the opposite of the input. In this (idealized) simulation, the CMOS inverter draws no current at all.
• CMOS Inverter (w/capacitance): In reality, there are two reasons that CMOS gates draw current. This circuit demonstrates the first reason: capacitance between the MOSFET gate and its source and drain. It requires current to charge this capacitance, which consumes power. It also causes a short delay when changing state.
• CMOS Inverter (slow transition): The other reason that CMOS gates draw current is that both transistors will conduct at the same time when the input is halfway between high and low. This causes a current spike when the input is in transition. In this circuit, there is a low-pass filter on the input which causes it to transition slowly, so you can see the spike.
• CMOS Transmission Gate: This circuit will pass any signal, even an analog signal (as long as it stays between 0 and 5 V) when the gate input is “H”. When it’s “L”, then the gate acts as an open circuit.
• CMOS Multiplexer: This circuit uses two transmission gates to select one of two inputs. If the logic input is “H”, then the output is a 40Hz triangle wave. If it’s “L”, then the output is a 80Hz sine wave.
• Sample-and-Hold: Click and hold the “sample” button to sample the input. When you release the button, the output level will be held constant.
• Delayed Buffer: This circuit delays any changes in its input for 15 microseconds.
• Leading-Edge Detector
• Switchable Filter: Click the “L” to select from two different low-pass filters.
• Voltage Inverter
• Inverter Amplifier: This shows how a CMOS inverter can be used as an amplifier.
• Inverter Oscillator
• Op-Amps
• Amplifiers
1. Inverting Amplifier: This one has a gain of –3.
2. Non-Inverting Amplifier
3. Follower
4. Differential Amplifier
5. Summing Amplifier
• Oscillators
1. Relaxation Oscillator
2. Phase-Shift Oscillator
3. Triangle Wave Generator
4. Sine Wave Generator
5. Sawtooth Wave Generator
6. Voltage-Controlled Oscillator: Here the frequency of oscillation depends on the input (shown in the scope on the left). The oscillator outputs a square wave and a triangle wave.
• Half-Wave Rectifier: An active rectifier that works on voltages smaller than a diode drop.
• Full-Wave Rectifier
• Peak Detector: This circuit outputs the peak voltage of the input. Whenever the input voltage is higher than the output, the output will be adjusted upward to match. Press the switch marked “reset” to reset the peak voltage back to 0.
• Integrator
• Differentiator
• Schmitt Trigger
• Negative Impedance Converter: Converts the resistor to a “negative” resistor. In the first graph, note that the current is 180° out of phase with the voltage.
• Gyrator: The top circuit simulates the bottom circuit without using an inductor.
• Capacitance Multiplier: This circuit allows you to simulate a large capacitor with a smaller one. The effective capacitance of the top circuit is C1 x (R1/R2), and the effective resistance is R2.
• Howland Current Source
• I-to-V Converter: The output voltage depends on the input current, which you can adjust with the switches.
• 741 Internals: The implementation of a 741 op-amp.
• 555 Timer Chip
• Square Wave Generator
• Internals: The implementation of a 555 chip, acting as a square wave oscillator
• Sawtooth Oscillator
• Low-duty-cycle Oscillator: produces short pulses.
• Monostable Multivibrator: This is a one-shot circuit that will produce a timed pulse when you click the “H”.
• Pulse Position Modulator: Produces pulses whose width is proportional to the input voltage.
• Active Filters
• VCVS Low-Pass Filter: An active Butterworth low-pass filter.
• VCVS High-Pass Filter
• Switched-Capacitor Filter: A digital filter, implemented using capacitors and analog switches.
• Logic Families
• RTL Logic Family
1. RTL Inverter: The white “H” is a logic input. Click on it to toggle its state. “H” means “high” (3.6 V) and “L” means “low” (0 V). The output of the inverter is shown at right, and is the opposite of the input.
2. RTL NOR: The three inputs are at the bottom, and the output is to the right. The output is “L” if any of the inputs are “H”. Otherwise it’s “H”.
3. RTL NAND: The output is “H” unless all three inputs are “H”, and then it’s “L”.
• DTL Logic Family
1. DTL Inverter
2. DTL NAND
3. DTL NOR
• TTL Logic Family
1. TTL Inverter
2. TTL NAND
3. TTL NOR
• NMOS Logic Family
1. NMOS Inverter
2. NMOS Inverter 2: This uses a second MOSFET instead of a resistor, to save space on a chip.
3. NMOS NAND
• CMOS Logic Family
1. CMOS Inverter
2. CMOS NAND
3. CMOS NOR
4. CMOS XOR
5. CMOS Flip-Flop (or latch): This circuit consists of two CMOS NAND gates.
6. CMOS Master-Slave Flip-Flop
• ECL Logic Family
1. ECL NOR/OR
• Combinational Logic
• Exclusive OR (XOR)
• Half Adder
• Full Adder
• 1-of-4 Decoder
• 2-to-1 Mux: This multiplexer uses two tri-state buffers connected to the output.
• Majority Logic: The output is high if a majority of the inputs are high.
• 2-Bit Comparator: Tells you if the two-bit input A is greater than, less than, or equal to the two-bit input B.
• 7-Segment LED Decoder
• Sequential Logic
• Flip-Flops
1. SR Flip-Flop
2. Clocked SR Flip-Flop
3. Master-Slave Flip-Flop
4. Edge-Triggered D Flip-Flop: This circuit changes state when the clock makes a positive transistion.
• Counters
1. 4-Bit Ripple Counter
2. 8-Bit Ripple Counter
3. Synchronous Counter
4. Decimal Counter
5. Gray Code Counter
6. Johnson Counter
• Divide-by-2: Divides the input frequency by 2.
• Divide-by-3
• LED Flasher: This circuit uses a Johnson counter to flash some LED’s in a back and forth pattern.
• Traffic Light
• Dynamic RAM: This is a simple model of a dynamic RAM chip. To read from the chip, select the bit you want using the row select lines. To write, select the data bit you want to write, and click the “write” switch. To refresh a bit, click the “refresh” switch.
• Analog/Digital
• Flash ADC: This is a direct-conversion, or “flash” analog-to-digital converter.
• Binary-Weighted DAC: Converts a four-bit binary number to a negative voltage.
• R-2R Ladder DAC
• Digital Sine Wave
• Phase-Locked Loops
• XOR Phase Detector: Shows an XOR gate being used as a type I phase detector. The output is high whenever the two input signals are not in phase.
• Type I PLL: This phase-locked loop circuit consists of an XOR gate (the phase detector), a low-pass filter (the resistor and capacitor), a follower (the op-amp), and a voltage-controlled oscillator chip. The voltage-controlled oscillator outputs a frequency proportional to the input voltage. After the PLL circuit locks onto the input frequency, the output frequency will be the same as the input frequency (with a small phase delay).
• Phase Comparator (Type II): Shows a more sophisticated phase detector, which has no output when the inputs are in phase, but outputs high (5V) when input 1 is leading input 2, and low (0V) when input 2 is leading input 1. The phase comparator and VCO in this applet are based on the 4046 chip.
• Phase Comparator Internals.
• Type II PLL: Shows a phase-locked loop with a type II phase detector. If you adjust the input frequency, the output should lock onto it in a short time.
• Type II PLL (fast): Just a faster simulation of the type II PLL.
• Frequency Doubler

Ändra/skapa Kretsar

För att lägga in en ny komponent, högerklicka i en oanvänd del av fönstret. Då får du en meny där du kan välja komponent (eller åtgärd). Sedan klickar du där du vill lägga första polen/kontakten och dra ut komponenten till där du vill ha den andra polen. Meny posterna låter dig skapa:

Add wire- lägga till ledare (tråd). Korsande trådar är inte sammankopplad om inte de möts på en ändpunkt.

Add resistor- lägg till resistor(er). Du kan välja resistans sedan genom att höger klicka och välja "edit"

Passive Components: capacitors = kondensatorer; inductor = spole; switch = strömbrytare; push switch= tryckströmbrytare; DPST switch= 2 polig växelkopplare; transformer = transformator

transistors transistorer

voltage sources,(spänningskällor)  1-terminal eller 2-terminal varianter. 1-terminal = en polig använder jord som den andra polen Med höger klick kan du bestämma spänning och vågform. Om det inte är DC = likspänning, kan du ställa in frekvens och pålagrad likspänning, DC offset.

op-amp, operationsförstärkare med matningsspänning gränser -15V och +15V. Man kan justera gränserna med högerklick och Edit.

text labels, Man måste "dra " lite när man lägger ut "Hello" som kan ändras (båda innehåll och storlek och "inverted" = överstreck) med högerklick och Edit.

scope probes; these have no effect on the circuit, but if you select them and use the right mouse menu item View in Scope, you can view the voltage difference between the terminals.

I undermenyn Other,finns det åtgärder som låter dig dra omkring: poler, rader eller kolumner med poler, markerade komponent, hela bilden. Det kan vara lämpligt att spara kretsen innan du provar dessa.

Spara och sammansätta kretsar

File meny låter dig spara eller stoppa in kretsbeskrivningar. Java säkerhetsregler brukar inte tillåta en applet att skriva filer på datorn. Om du väljer File->Export så öppnas ett litet fönster med beskrivningen av kretsen som du kan kopiera och klistra in i Notepad eller annat program som kan spara text filer. Början kan se ut som:

$ 1 5.0E-6 10.391409633455755 43 5.0 50
w 224 80 320 80 0

Jag fann att det inte kunde importeras om man inte ändrade talet efter "$ 1 5.0E-6" till ett heltal, så här:

$ 1 5.0E-6 10 43 5.0 50

Sedan kan du spara filen. Om du sedan kopierar den och klistra in den i Import för att ladda in den.

Om man har flera liknande småkretsar som man vill visa i en simulering, kan man rita en i ett hörn (Lägg inte in oscilloskopen ännu) och exportera den. Sedan dra den till en ledig plats och göra de ändringar du vill och exportera den och klistra in den i slutet av föregående fil. Ta bort inledningsraden för den andra kretsen! Nu har du en fil som ritar upp båda samtidigt.

Till appletsidan i kursen (men den finns nog redan i ett annat fönster).