Electronics design calculators

Featured calculators

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  LED Series Resistor Calculator

  Size the series resistor for one LED string from supply voltage, forward voltage and current, then pick a nearby E-series value and check resistor power.

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  Voltage Divider Calculator

  Find the tap voltage of a two-resistor divider, see how a load pulls that tap down, and check the current and power in each resistor.

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  Resistor Color Code Decoder

  Decode 4-, 5- and 6-band through-hole resistor colour codes to resistance, tolerance and optional TCR.

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  Parallel Resistor Calculator

  Combine resistors in parallel or series. See the equivalent resistance and the conductance of the network.

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  555 Timer Calculator

  Astable and monostable NE555 timing with exact ln(2) and ln(3), plus reverse astable from frequency and duty cycle.

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  Ohm's Law Calculator

  Solve any two of voltage, current, resistance and power from the other two using V = I R and P = V I.

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• LED Series Resistor Calculator

  Size the series resistor for one LED string from supply voltage, forward voltage and current, then pick a nearby E-series value and check resistor power.

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• Voltage Divider Calculator

  Find the tap voltage of a two-resistor divider, see how a load pulls that tap down, and check the current and power in each resistor.

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• Resistor Color Code Decoder

  Decode 4-, 5- and 6-band through-hole resistor colour codes to resistance, tolerance and optional TCR.

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• Parallel Resistor Calculator

  Combine resistors in parallel or series. See the equivalent resistance and the conductance of the network.

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• 555 Timer Calculator

  Astable and monostable NE555 timing with exact ln(2) and ln(3), plus reverse astable from frequency and duty cycle.

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• Ohm's Law Calculator

  Solve any two of voltage, current, resistance and power from the other two using V = I R and P = V I.

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• AMS1117-ADJ Calculator – Resistors, Dropout & Heat Check

  Pick AMS1117-ADJ resistors with standard values, then check dropout, the 10 mA minimum load and junction temperature before you build.

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• AWG Wire Size Calculator

  ASTM B258 American Wire Gauge geometry — diameter, area and circular mils from gauge, or gauge from diameter or area.

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• Battery Life Calculator

  Estimate run-time from battery capacity in mAh, average load current and an optional derating factor.

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• Bridged-Tee Attenuator Calculator

  Matched bridged-T pad with arms fixed at Z0. Only the bridge and shunt snap to E96. A above 60 dB is theoretical.

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• Capacitance Converter

  Convert farads, microfarads, nanofarads and picofarads, and decode IEC 60062 3-digit capacitor markings such as 104, 1R5 and 109.

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• Capacitor Calculator

  Capacitive reactance Xc at a frequency and RC time constant τ from resistance and capacitance.

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• Capacitor Discharge Calculator

  Safety discharge time or bleeder resistor from V(t) = V0 e^(−t/RC). Default 60 V is an IEC 62368-1 ES1 DC reference, not a hard legal limit.

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• Capacitor Energy Calculator

  Stored energy E = ½ C V² and charge Q = C V. Optional R also reports the RC time constant.

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• CH340 Selector – CH340G vs C vs E vs B, Pinout & 3.3 V Use

  Pick the right CH340 variant by crystal, package, modem lines, temperature and 3.3 V supply, with the WCH pin differences and baud-error figures for each.

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• Current Divider Calculator

  Split a source current among parallel resistors. Ik = I·(1/Rk)/Σ(1/Ri). A 0 Ω branch is a short and is rejected.

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• dBm to Watts Converter

  Convert between dBm, watts and dBW. 0 dBm is 1 mW; 30 dBm is 1 W; dBW = dBm − 30.

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• Heat Sink Temperature Calculator

  JEDEC JESD51 stack Tj = Ta + P(θJC+θCS+θSA), Pmax, and the θSA required to stay under Tjmax. No uncited package θ table.

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• Inverting Op-Amp Resistor Calculator

  Design R2 = |G|·R1 and bias-compensation R3 = R1 for a target inverting gain, with optional level-shift R4 and nearest E24/E96.

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• LM2596-ADJ Calculator – Feedback Resistors, Inductor E·T, Min VIN

  Set LM2596-ADJ output with standard resistors, get the inductor E·T value TI uses, and check minimum input voltage for TI, onsemi or XL2596 parts.

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• MP1584 Calculator (NRFND) – Resistors, RFREQ, Inductor + MP2338 Notes

  Set MP1584 output and frequency resistors, size the inductor and check the 100 ns minimum on-time. MPS lists MP1584 as not recommended for new designs; see what changes with MP2338.

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• Op-Amp Voltage and Gain Calculator

  Ideal four-resistor op-amp superposition (Sedra/Smith) with differential, inverting and non-inverting presets, then clip Vout to the rails.

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• PCB Trace Width Calculator

  IPC-2221A internal and external copper trace width from current, copper weight and temperature rise, with DC resistance at Tamb + ΔT.

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• Pi Attenuator Calculator

  Matched π-pad resistors from A and Z0, plus nearest E96 and the back-calculated voltage attenuation. A above 60 dB is theoretical.

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• Electrical Power Calculator

  Compute DC power and the third quantity from any two of voltage, current and resistance using P = VI, I²R and V²/R.

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• RC Time Constant Calculator

  τ = R C with charge and discharge voltages at 1τ through 5τ, stored energy, charge and cutoff frequency.

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• Reactance Calculator

  Xc = 1/(2π f C) and Xl = 2π f L, plus inverse L or C from X and f, and susceptance |B| = 1/|X| in siemens. Frequency in Hz–GHz.

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• Reflection Attenuator Calculator

  Reflection pad Rhi/Rlo from A and Z0. Requires a 90° hybrid coupler. A above 60 dB is theoretical.

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• Series and Parallel Capacitor Calculator

  Parallel Cp = Σ Ci and series 1/Cs = Σ 1/Ci from a list of capacitors. Series mode always flags unequal DC voltage sharing.

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• SMD Resistor Code Calculator

  Decode EIA-3, EIA-4, EIA-96 and R-notation SMD resistor markings. Ambiguous codes such as 10R show both readings.

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• Tee Attenuator Calculator

  Matched T-pad resistors from A and Z0, plus nearest E96 and the back-calculated voltage attenuation. A above 60 dB is theoretical.

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• TL431 Calculator – Output Voltage & Cathode Resistor Window

  Calculate TL431 divider resistors with Iref error, the valid cathode-resistor range for your input and load, and SOT-23 power and temperature rise.

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• TP4056 Charge Current Calculator – RPROG, Heat & Cutoff

  Set TP4056 charge current from RPROG, check chip temperature at your battery voltage, and see why "1.2k = 1A" tables disagree with the datasheet.

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• Electronics Unit Converter

  Convert resistance, voltage, current, capacitance, inductance, frequency, time, power and energy with SI prefixes.

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Learning guides

Short notes on formulas, passive values, and common footprints — each linked to a calculator where it helps.

• Battery capacity and runtime

  Convert mAh to runtime with load current and efficiency factors.

• Capacitive and inductive reactance

  Xc and Xl at a frequency with links to the reactance calculator.

• Capacitor types for bypass and bulk

  Ceramic, electrolytic, and film capacitors — where each belongs in a board.

• Common SMD package sizes

  Footprint codes for resistors, capacitors, and small ICs — facts only, no substitution guarantees.

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