Electrical Components
This section covers the passive and active electrical components used to build LED circuits and general hobby electronics — resistors, capacitors, diodes, transistors, bridge rectifiers, relays, and 555 timers. Every component ships individually so you can source exactly the value you need.
- Resistors — 227 values across four wattage ratings: 1/4W, 1/2W, 1W, and 1/8W 0805 SMD. The most commonly used component in LED circuits — a current-limiting resistor is required any time you connect an LED directly to a DC supply.
- Capacitors — aluminum electrolytic, ceramic disc, and multi-layer ceramic (MLCC). Used for AC-to-DC smoothing, RC timing networks in 555 blinker circuits, and IC decoupling on microcontroller boards. See the power supply filter guide and decoupling capacitor guide for wiring details.
- Diodes — zener, general purpose, and Schottky. Used for reverse-polarity protection, voltage clamping, and flyback suppression on relay coils.
- Transistors — BJT NPN and BJT PNP. Commonly used to switch higher-current LED loads from a low-current microcontroller output (Arduino, Raspberry Pi GPIO) or to drive relay coils.
- Bridge Rectifiers — the MB1S mini bridge rectifier converts AC or DCC track power to pulsed DC so you can run LEDs and animated pre-wired LEDs from landscape transformers or model railroad layouts. See the full AC/DCC wiring guide for circuit diagrams.
- Relays — DC relays for switching high-current LED loads, motor circuits, and automotive accessories from a low-current control signal.
- Timers / Controllers — the 555 timer IC, the classic astable oscillator for building adjustable LED flashers and blinkers without a microcontroller. See the 555 timer LED blinker guide for a complete circuit with resistor and capacitor value tables.
Frequently Asked Questions
Yes — unless the LED already has one built in. An LED has no internal resistance to limit current, so connecting one directly to a DC supply will overdraw current and burn it out within seconds. The only exceptions are 12V built-in resistor LEDs and pre-wired LEDs, which include the resistor on the wire. For all standard component LEDs, calculate your resistor value using: R = (Vsupply − Vf) ÷ If, where Vf is the LED forward voltage and If is the desired current (typically 20 mA for standard LEDs).
An aluminum electrolytic capacitor. Electrolytics offer high capacitance (10 μF–1000 μF) in a compact radial package, which is exactly what you need to smooth the ripple from pulsed DC output. A 100 μF capacitor is the standard starting value for LED circuits powered from a bridge rectifier on a 12V AC landscape transformer or DCC track. Ceramic disc and MLCC capacitors are too small (typically under 1 μF) for smoothing — use those for IC decoupling and high-frequency bypass instead. See the power supply filter guide for capacitor sizing details.
A bridge rectifier is a four-diode arrangement that converts AC (alternating current) into pulsed DC. You need one any time your power source is AC rather than DC — common situations include 12V AC landscape transformer circuits, DCC model railroad track power (which is a bipolar square wave, not DC), and some older power supplies. Without rectification, standard LEDs will either flicker at line frequency or not light at all, and animated pre-wired LED ICs will not run correctly. The MB1S is a single-package surface-mount bridge rectifier designed for exactly these applications. See the AC/DCC wiring guide for a step-by-step circuit.
Both are bipolar junction transistors (BJTs) used as electronic switches, but they conduct in opposite directions. An NPN transistor switches ON when a positive voltage is applied to its base — current flows from collector to emitter, and the load (LED, relay coil) sits between the positive supply and the collector. A PNP transistor switches ON when the base is pulled LOW relative to the emitter — current flows from emitter to collector, and the load sits between the collector and ground. For most LED and relay-switching applications with Arduino or Raspberry Pi GPIO, an NPN transistor in a low-side switch configuration is the simpler choice.
In astable (free-running oscillator) mode, a 555 timer produces a continuous square wave output that switches an LED on and off at a rate you set with two resistors and a capacitor. Flash rate is adjustable from under 0.1 Hz (one blink every 10+ seconds) to several hundred Hz, making it useful for slow warning blinkers, scale model signal lights, and fast strobe effects. No microcontroller or code required — just the 555 IC, two resistors, a capacitor, and a power supply. See the 555 timer LED blinker guide for a complete circuit schematic and value tables.
A general purpose diode (such as the 1N4148) conducts current in one direction only — it blocks reverse current below its breakdown voltage. Common uses: reverse-polarity protection for LED circuits, and flyback suppression (wired across a relay coil to absorb the voltage spike when the coil de-energises). A zener diode is designed to operate in reverse breakdown at a precise voltage (e.g. 5.1 V, 12 V), making it useful as a simple voltage reference or low-current voltage regulator. Schottky diodes have a very low forward voltage drop (~0.2 V vs. ~0.7 V for silicon) and fast switching — used in high-frequency rectifier and protection circuits.