Electrical

12 tools: Ohm's law (full solver), resistor color code (4-band → resistance, plus reverse), voltage drop on wire, AWG wire gauge sizing, LED series resistor, RC and RL time constants, decibel (power or voltage ratio), power factor, battery life (mAh ÷ load), and solar panel sizing for off-grid loads.

4-band: digit-digit-multiplier-tolerance. Pick the colors in the Resistor Color Code calculator → get resistance + tolerance. There's also a reverse calculator: type the resistance value, get the colors.

R = (Vsupply − Vled_forward) / Iled. The LED Series Resistor calculator does this for you — also outputs the power dissipated so you can pick a 1/4-watt or 1/2-watt resistor.

Battery life ≈ (capacity in mAh / load in mA) × efficiency factor (~0.7). The Battery Life calculator includes the factor. For lithium-ion, real-world usable capacity is 80-90% of rated.

Required watts = (daily energy kWh × 1000) / (peak sun hours × system efficiency). Type your daily kWh load and local sun-hours; the calculator outputs required panel watts and how many 300W panels that translates to.

Long wires drop voltage proportional to current × resistance. The Voltage Drop calculator uses wire material (copper vs aluminium) and length to estimate drop — typically should stay under 3% for branch circuits per electrical code.