https://circuitnote.com/Quick electronics calculators for lab work and circuit design. Free, no sign-up, works in your browser.en https://circuitnote.com/ammeter-reads-lowhttps://circuitnote.com/ammeter-reads-lowWhy a series circuit's measured current comes out 1–3% below the Ohm's law value, split into resistor tolerance, ammeter burden and meter accuracy using real lab measurements.Tue, 03 Nov 2026 09:00:00 +0900 https://circuitnote.com/breadboard-troubleshootinghttps://circuitnote.com/breadboard-troubleshootingA step-by-step order for debugging a digital logic breadboard: split power rails, IC power pins, floating inputs, logic levels, loose jumpers and 7-segment displays.Tue, 03 Nov 2026 09:00:00 +0900 https://circuitnote.com/rectifier-ripplehttps://circuitnote.com/rectifier-rippleWhy a full-wave rectifier with a small capacitor shows less ripple than the textbook estimate, explained with PSpice results and a discharge model, plus when the estimate is safe to use.Tue, 03 Nov 2026 09:00:00 +0900 https://circuitnote.com/diode-cut-inhttps://circuitnote.com/diode-cut-inFitting diode current and voltage data to an exponential model shows why the cut-in voltage depends on current, and how it sets the drop in a half-wave rectifier.Tue, 03 Nov 2026 09:00:00 +0900 https://circuitnote.com/universal-gateshttps://circuitnote.com/universal-gatesHow to wire AND, OR and NOT from a 7400 (NAND) or 7402 (NOR), with measured output voltages, the switching threshold, and why a square wave looks tilted on the scope.Tue, 03 Nov 2026 09:00:00 +0900 https://circuitnote.com/active-lowhttps://circuitnote.com/active-lowFunction tables, pin numbers and LED wiring for the 74LS147 priority encoder and 74LS42 decoder, whose inputs and outputs are active on Low.Tue, 03 Nov 2026 09:00:00 +0900 https://circuitnote.com/mux-adderhttps://circuitnote.com/mux-adderHow to choose a 74153 multiplexer's data inputs from a truth table, the strobe pins to watch, and measured full adder results.Tue, 03 Nov 2026 09:00:00 +0900 https://circuitnote.com/zener-regulatorhttps://circuitnote.com/zener-regulatorWhy a zener diode regulator's output drops when the load resistance is too small, explained with 1N4734 simulation and bench results: minimum load resistance, output resistance, power in the zener and resistor, and when to use absolute rather than percent error.Tue, 03 Nov 2026 09:00:00 +0900 https://circuitnote.com/bjt-betahttps://circuitnote.com/bjt-betaHow an NPN transistor's β changes with current and from part to part, the Early effect and the saturation region, read from simulated and measured currents, and what that means for amplifier and switch design.Tue, 03 Nov 2026 09:00:00 +0900 https://circuitnote.com/bjt-biashttps://circuitnote.com/bjt-biasHand calculations of the 2N3904 operating point with and without an emitter resistor, checked against PSpice and breadboard measurements on the load line, and how far the collector current moves when β changes.Thu, 05 Nov 2026 09:00:00 +0900 https://circuitnote.com/bjt-amplifierhttps://circuitnote.com/bjt-amplifier2N3904 common-emitter and common-collector gains, simulated and measured, against the −(RC‖RL)/RE estimate and the formula with rπ, and why a gain −10 design comes out near −9.5.Thu, 05 Nov 2026 09:00:00 +0900 https://circuitnote.com/oscilloscope-basicshttps://circuitnote.com/oscilloscope-basicsThe function generator and oscilloscope lab: probe compensation, DC versus AC coupling, how to measure and the usual slips, with the Vpp and frequency values the scope actually displayed.Thu, 05 Nov 2026 09:00:00 +0900 https://circuitnote.com/pspice-basicshttps://circuitnote.com/pspice-basicsSetting up PSpice bias point, DC sweep, transient and AC sweep analyses, checking each result by hand, and the settings that trip people up: ground, MEG, AC magnitude and step size.Tue, 03 Nov 2026 09:00:00 +0900 https://circuitnote.com/mosfet-ivhttps://circuitnote.com/mosfet-ivThe 2N7000 enhancement N-channel MOSFET's ID–VDS and ID–VGS curves from PSpice, how to get the threshold voltage and K from a √ID plot, XY-mode measurement and the usual breadboard slips.Thu, 05 Nov 2026 09:00:00 +0900 https://circuitnote.com/mosfet-biashttps://circuitnote.com/mosfet-biasOperating points of 2N7000 voltage-divider and self-bias circuits from the square law, how far one resistor, a threshold spread or a meter on the gate moves them, and designing for a target point.Thu, 05 Nov 2026 09:00:00 +0900 https://circuitnote.com/mosfet-amplifierhttps://circuitnote.com/mosfet-amplifierOperating point, gm and voltage gain of 2N7000 common-source and common-drain amplifiers against PSpice, when the quick estimate fails, a gain −10 design, and how a real part's threshold wrecks the bias.Thu, 05 Nov 2026 09:00:00 +0900 https://circuitnote.com/mosfet-active-loadhttps://circuitnote.com/mosfet-active-loadHow a PMOS current mirror's reference resistor sets its output current, the active-load common-source gain against PSpice, why the bias point sticks to a rail on a breadboard, heat, and making a tiny input signal.Thu, 05 Nov 2026 09:00:00 +0900 https://circuitnote.com/practicehttps://circuitnote.com/practicePractice problems in six units: Ohm's law, series and parallel resistors, voltage dividers, RC circuits, diodes and BJT basics. Multiple choice and numeric answers, graded instantly with step-by-step solutions; scores stay on your device.Tue, 03 Nov 2026 09:00:00 +0900 https://circuitnote.com/practice-ohmhttps://circuitnote.com/practice-ohm10 Ohm's law and power practice problems: current, voltage, resistance, dissipated power, choosing a power rating and an LED resistor. Multiple choice and numeric answers, graded with step-by-step solutions.Tue, 03 Nov 2026 09:00:00 +0900 https://circuitnote.com/practice-serieshttps://circuitnote.com/practice-series10 series and parallel resistor practice problems: two and three resistors in parallel, mixed networks, circuit current, capacitors in series and finding the parallel resistor for a target. Graded, with step-by-step solutions.Tue, 03 Nov 2026 09:00:00 +0900 https://circuitnote.com/practice-dividerhttps://circuitnote.com/practice-divider9 voltage divider practice problems: output voltage, choosing resistors for a target, loading, current draw, scaling for an ADC input and Thévenin resistance. Graded, with step-by-step solutions.Tue, 03 Nov 2026 09:00:00 +0900 https://circuitnote.com/practice-rchttps://circuitnote.com/practice-rc10 RC circuit practice problems: time constant, charging and discharging voltage, time to half, the 5τ rule, cutoff frequency and filter design, the −3 dB output and phase. Graded, with step-by-step solutions.Tue, 03 Nov 2026 09:00:00 +0900 https://circuitnote.com/practice-diodehttps://circuitnote.com/practice-diode10 diode practice problems: forward current, reverse bias, half-wave and bridge rectifier output, smoothing ripple, zener series resistor and power, temperature, LED resistor and the exponential law. Graded, with step-by-step solutions.Tue, 03 Nov 2026 09:00:00 +0900 https://circuitnote.com/practice-bjthttps://circuitnote.com/practice-bjt10 BJT transistor practice problems: collector current and β, emitter current, base resistor for a switch, saturation voltage, collector-emitter voltage, voltage-divider bias, operating region, power and common-emitter gain. Graded, with step-by-step solutions.Tue, 03 Nov 2026 09:00:00 +0900 https://circuitnote.com/ohmhttps://circuitnote.com/ohmEnter any two of voltage, current, resistance and power to get the rest, plus the resistor power rating you need.Thu, 05 Nov 2026 09:00:00 +0900 https://circuitnote.com/dividerhttps://circuitnote.com/dividerCalculate a voltage divider's output from the input voltage and two resistors, and find the E24 standard resistor pair closest to your target voltage.Tue, 10 Nov 2026 09:00:00 +0900 https://circuitnote.com/serieshttps://circuitnote.com/seriesEnter several resistor or capacitor values to get their series and parallel equivalents at once.Wed, 04 Nov 2026 09:00:00 +0900 https://circuitnote.com/labhttps://circuitnote.com/labPaste lab measurements from Excel or Google Sheets and get the theory values, a percent-error table and a report-ready graph. RC time constant, RC filter cutoff, Ohm's law, voltage divider, op-amp gain and free-form comparison, with PNG, CSV and table export.Tue, 03 Nov 2026 09:00:00 +0900 https://circuitnote.com/errorhttps://circuitnote.com/errorCalculate percent error between theoretical and measured values for lab reports, plus mean, standard deviation and standard error of repeated measurements.Tue, 03 Nov 2026 09:00:00 +0900 https://circuitnote.com/sigfighttps://circuitnote.com/sigfigCount significant figures, see which digits are significant, and round any number to a chosen number of significant figures without floating-point errors.Tue, 03 Nov 2026 09:00:00 +0900 https://circuitnote.com/dmmhttps://circuitnote.com/dmmConvert a digital multimeter accuracy spec such as ±(0.8% + 3 digits) into an uncertainty range for your reading, and check a theoretical value against it.Tue, 03 Nov 2026 09:00:00 +0900 https://circuitnote.com/resistorhttps://circuitnote.com/resistorResistor color (colour) code calculator: pick the bands to get the resistance and tolerance range, or enter a value to find its 4-band or 5-band colors. Includes a color code chart and the bands of common values like 220 Ω, 1 kΩ and 10 kΩ.Wed, 04 Nov 2026 09:00:00 +0900 https://circuitnote.com/smdhttps://circuitnote.com/smdDecode SMD chip resistor markings in 3-digit, 4-digit and EIA-96 format, or find the code for any resistance.Tue, 03 Nov 2026 09:00:00 +0900 https://circuitnote.com/capcodehttps://circuitnote.com/capcodeDecode ceramic and film capacitor codes such as 104 or 472J into pF, nF and µF with tolerance, or find the code for a capacitance.Tue, 03 Nov 2026 09:00:00 +0900 https://circuitnote.com/rchttps://circuitnote.com/rcCalculate the −3 dB cutoff frequency and time constant of a first-order RC or RL low-pass or high-pass filter.Tue, 03 Nov 2026 09:00:00 +0900 https://circuitnote.com/opamphttps://circuitnote.com/opampCalculate the voltage gain, gain in dB and output voltage of inverting and non-inverting op-amp amplifiers, and check for clipping.Tue, 03 Nov 2026 09:00:00 +0900 https://circuitnote.com/timer555https://circuitnote.com/timer555Calculate the output frequency, period, high and low times and duty cycle of an NE555 astable circuit from R1, R2 and C.Tue, 03 Nov 2026 09:00:00 +0900 https://circuitnote.com/lchttps://circuitnote.com/lcCalculate the resonant frequency of an LC circuit, its characteristic impedance, and the inductive and capacitive reactance at any frequency.Tue, 03 Nov 2026 09:00:00 +0900 https://circuitnote.com/biashttps://circuitnote.com/biasCalculate the Q-point of a voltage-divider biased NPN transistor: base and collector current, VCE, node voltages and operating region, with the DC load line and how much IC moves when β changes.Thu, 05 Nov 2026 09:00:00 +0900 https://circuitnote.com/bjthttps://circuitnote.com/bjtCalculate the base resistor for an NPN transistor switch driven from an Arduino or other microcontroller pin, with base current and forced beta.Wed, 04 Nov 2026 09:00:00 +0900 https://circuitnote.com/dbhttps://circuitnote.com/dbConvert decibels to power and voltage ratios and back, and convert dBm to watts, dBW and volts into 50 Ω.Thu, 05 Nov 2026 09:00:00 +0900 https://circuitnote.com/adchttps://circuitnote.com/adcConvert ADC readings to voltage and voltage to ADC codes for 8 to 24-bit converters, including Arduino analogRead(), ESP32 and STM32.Tue, 03 Nov 2026 09:00:00 +0900 https://circuitnote.com/pinouthttps://circuitnote.com/pinoutTop-view pin diagrams for common 74-series logic ICs, flip-flops, counters, the 555 timer and op-amps, with power pins, active-low pins and wiring notes for breadboard labs.Tue, 03 Nov 2026 09:00:00 +0900 https://circuitnote.com/basehttps://circuitnote.com/baseConvert numbers between binary, octal, decimal and hexadecimal instantly, with binary grouped in nibbles and the number of bits needed.Tue, 03 Nov 2026 09:00:00 +0900 https://circuitnote.com/twoshttps://circuitnote.com/twosConvert signed decimal numbers to two's complement binary and hex for 4, 8, 16 or 32 bits with each step shown, and read the signed value of any bit pattern.Tue, 03 Nov 2026 09:00:00 +0900 https://circuitnote.com/seg7https://circuitnote.com/seg7See which segments of a 7-segment display light for 0–F, the BCD input, and the hex byte for common-cathode or common-anode displays driven from Arduino or a 74LS47.Tue, 03 Nov 2026 09:00:00 +0900 https://circuitnote.com/aluhttps://circuitnote.com/aluSimulate a 4-bit arithmetic logic unit: choose s1, s0 and Cin to add, subtract, increment or decrement, or pick OR, XOR, AND and NOT, and get F and the carry out.Tue, 03 Nov 2026 09:00:00 +0900 https://circuitnote.com/ledhttps://circuitnote.com/ledWhat resistor does an LED need? A red LED on 5 V at 20 mA needs 150 Ω and a white LED 91 Ω. Calculate the current-limiting resistor and wattage for any supply, LED color, current and LEDs in series, with charts.Wed, 04 Nov 2026 09:00:00 +0900 https://circuitnote.com/batteryhttps://circuitnote.com/batteryA 6000 mAh battery lasts about 51 hours at 100 mA and 10.2 hours at 500 mA. Work out battery life in hours for any mAh and current, with tables from 500 to 20000 mAh, phone screen time and power bank charges.Tue, 03 Nov 2026 09:00:00 +0900 https://circuitnote.com/wirehttps://circuitnote.com/wireCalculate voltage drop, percentage loss and heat in copper or aluminium wire from AWG or mm² size, length and current.Tue, 03 Nov 2026 09:00:00 +0900 https://circuitnote.com/tracehttps://circuitnote.com/traceCalculate the minimum PCB trace width for a given current, temperature rise and copper weight using IPC-2221, with trace resistance and voltage drop.Tue, 03 Nov 2026 09:00:00 +0900 https://circuitnote.com/pcb-generatorhttps://circuitnote.com/pcb-generatorFree online PCB generator with three templates: a MOSFET low-side switch, a 555 LED blinker and an LM317 adjustable supply. Enter voltages and currents to get the parts chosen, traces sized, a heatsink check, schematic, board preview, parts list and Gerber + drill files ready to order.Tue, 03 Nov 2026 09:00:00 +0900 https://circuitnote.com/dcdchttps://circuitnote.com/dcdcCalculate the inductor value, duty cycle, ripple and peak current for buck (step-down) and boost (step-up) DC-DC converters.Tue, 03 Nov 2026 09:00:00 +0900 https://circuitnote.com/recthttps://circuitnote.com/rectCalculate the output voltage, peak-to-peak ripple and required smoothing capacitor for half-wave, center-tap and bridge rectifiers, with the output waveform.Wed, 04 Nov 2026 09:00:00 +0900 https://circuitnote.com/zenerhttps://circuitnote.com/zenerCalculate the series resistor for a zener diode regulator or reference, with the resistor and zener power ratings.Tue, 10 Nov 2026 09:00:00 +0900 https://circuitnote.com/heatsinkhttps://circuitnote.com/heatsinkCalculate the heatsink thermal resistance you need from power dissipation, junction and ambient temperature, θjc and θcs, and check if a heatsink is needed.Thu, 05 Nov 2026 09:00:00 +0900