Electronics design calculators

electronics.tools is a small set of design calculators and learning notes for circuit work. Every tool runs in your browser. Nothing is stored, and there are no accounts.

Featured calculators

• Resistor Color Code Decoder

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

• 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.

• Battery Life Calculator

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

• 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.

• Capacitor Calculator

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

• 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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Cross-reference

Datasheet-checked equivalents and SOT-23 marking notes. A verdict only applies under the conditions listed with it.

• AMS1117 Equivalents – Datasheet-Checked Pin-Compatible Parts

  TI LM1117, ST LD1117 and JSCJ CJT1117B checked line by line against the AMS1117 datasheet: SOT-223 pinout, dropout, min load, capacitor and heat.

• CH340G Alternatives – CH340C, CH340E, CP2102, FT232RL Compared

  What changes when you swap a CH340G: pinout, crystal, supply, baud rate, temperature and USB IDs for CH340C, CH340E, CP2102 and FT232RL, from each datasheet.

• LM2596 Equivalents – TI vs onsemi vs XL2596 Checked

  TI LM2596, onsemi LM2596 and XLSEMI XL2596 compared pin by pin: saturation voltage, duty cycle, current limit and ON/OFF thresholds. XL1509 needs a new layout.

• TL431 SOT-23 Marking Codes (T3C3, TAC3, T3G3) & Pinout

  Decode TI TL431/TL432 SOT-23 (DBZ) markings into grade (0.5/1/2%) and temperature range, from TI's package addendum, and avoid the TL431 vs TL432 pin swap.

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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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Component categories

Selection criteria and widely used part numbers to orient a BOM — not a catalog or storefront.

• Buck (step-down) converters

  Switching regulators for efficient step-down rails.

• Ceramic capacitors (MLCC)

  Dielectrics, voltage derating, and bypass placement.

• Electrolytic capacitors

  Bulk input and output capacitors — ripple, ESR, and lifetime.

• General-purpose diodes

  Rectifiers and switching diodes for protection and ORing.

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