Electronics lab notes, checked on a real bench
CircuitNote is run by an electronics student who measures the circuits from lab classes and writes up what the numbers really showed: diode curves, zener regulators under load, BJT bias points against PSpice. Around those guides sit 32 calculators, practice problems and a PCB generator. Free, no sign-up, and nothing you type is stored or sent anywhere.
What you won't find on a plain calculator site
Lab guides from real measurements17 guides written from values measured in lab classes, showing where theory, PSpice and the bench disagree.
PCB generatorPick a circuit, set the values and download Gerber files for a board that passes a design-rule check: MOSFET switch, 555 LED blinker, LM317 supply.
Practice problems with solutions6 units, graded in your browser, with every answer and worked solution computed rather than typed.
Lab guides 17
- G1Why your ammeter reads less current than you calculatedResistor tolerance, ammeter burden and meter accuracy, with real data
- G2Breadboard circuit not working? A checking orderPower rails, pinouts, logic levels and loose jumpers, in order
- G3Why rectifier ripple comes out smaller than the textbook formulaRectifier ripple: why the estimate and simulation disagree
- G4Where does the 0.7 V diode cut-in voltage come from?The diode cut-in voltage, seen in real I–V data
- G5Building AND, OR and NOT from NAND or NOR gates (measured)Universal gate wiring with measured voltages
- G6Making sense of active-low: the 74LS147 encoder and 74LS42 decoder74LS147 and 74LS42 tables, and how to read active-low
- G7A half adder and a full adder from one 74153 multiplexerAdders from a 74153: choosing the data inputs
- G8Why a zener regulator collapses under a heavy loadMinimum load resistance and zener heat, with real numbers
- G9Why transistor β (hFE) is not a constantβ spread, Early voltage and saturation, in numbers
- G10BJT biasing: why a voltage-divider bias gets an emitter resistorOperating point by hand, and bias that survives β spread
- G11Common-emitter gain: how good is the quick estimate?CE and CC gain: the estimate against the full formula
- G12First oscilloscope lab: probe compensation, DC vs AC coupling and reading VppProbe compensation, coupling and Vpp, with real screen values
- G13PSpice's four basic analyses: bias point, DC sweep, transient and AC sweepSettings, hand checks and the usual stumbling blocks
- G14Enhancement MOSFET I–V curves: reading the threshold voltage and KRegions, the threshold from a √ID plot, XY-mode measurement
- G15MOSFET biasing: why voltage-divider bias is so sensitive to the threshold voltageOperating point, threshold spread and what a source resistor buys
- G16MOSFET common-source and common-drain amplifiers: gain formulas, PSpice and the threshold voltagegm and the gain formulas, source follower, a gain −10 design, DC point first
- G17MOSFET current mirror and active-load amplifier: what a gain of hundreds costsCurrent mirror, the gain formula, trimming the bias, heat
Practice problems 6
- EXAll unitsSix units, graded, with step-by-step solutions
- EX1Ohm's law and powerV = IR, power and ratings in 10 problems
- EX2Series and parallelEquivalent resistance and mixed networks, 10 problems
- EX3Voltage dividerOutput voltage, loading and ADC scaling, 9 problems
- EX4RC circuitsTime constant, charging and cutoff, 10 problems
- EX5DiodesRectifiers, ripple, zeners and LEDs, 10 problems
- EX6BJT basicsBeta, switches, bias and gain, 10 problems
Calculators 32
Basics 3
Lab measurements 4
Component codes 3
Filters, timers and amplifiers 6
- fcRC and RL cutoffFirst-order filter cutoff and time constant
- U1Op-amp gainInverting and non-inverting gain and output
- U2555 timerAstable frequency and duty cycle
- LCLC resonanceResonant frequency and reactance
- QBJT bias (Q-point)Q-point IC and VCE of a divider-biased NPN
- Q1Transistor base resistorBase resistor for an NPN switch
Signals and conversion 2
Digital logic 5
Power, wiring and PCB 9
- D1LED resistorCurrent-limiting resistor and wattage
- BATBattery lifeRuntime from capacity, current and sleep time
- AWGWire voltage dropVoltage drop and heat in a cable
- IPCPCB trace widthTrace width for a current, per IPC-2221
- PCBPCB generator (MOSFET, 555, LM317)MOSFET switch, 555 blinker or LM317 supply board, with Gerber files
- L1Buck and boost inductorInductance, duty cycle and peak current
- D~Rectifier rippleRipple and smoothing capacitor for a rectifier
- DZZener resistorSeries resistor and power for a zener
- θSAHeatsinkRequired heatsink °C/W and junction temperature
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