Free online LED resistor calculator. Find the correct resistor value for single, series, parallel, and mixed LED circuits. Enter a SKU to auto-fill LED specs.
March 2026
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Which Voltage Pre-Wired LED Do I Need? Complete Power Source Guide
Complete guide to choosing the right voltage pre-wired LED for your power source. Quick reference table: 12V for automotive and model railroad, 9V for guitar pedals, 6V for Arduino and USB. -
555 Timer LED Blinker: How the RC Timing Network Controls Blink Rate
Technical deep dive into the 555 timer astable circuit. Explains how Ra, Rb, and C set the blink rate through charge and discharge cycles, with formulas, circuit diagram, and component selection guide. -
Power Supply Filter Capacitor: Smoothing Ripple from a Bridge Rectifier
How filter capacitors smooth pulsed DC from a bridge rectifier into clean DC. Covers ripple voltage formula, capacitor sizing, and practical power supply design for LED and audio circuits. -
Decoupling Capacitors: Eliminating Power Supply Noise on IC Circuits
Why every IC needs decoupling capacitors and how to choose and place them. Covers the two-capacitor strategy (100nF ceramic + 10uF electrolytic), placement rules, and common mistakes. -
Using LEDs with AC Power: Bridge Rectifiers and Smoothing Capacitors Explained
How to power LEDs from AC sources (landscape transformers, DCC track power) using a bridge rectifier and smoothing capacitor. Covers both pre-wired and component LEDs with circuit diagrams.