Skip to content

Blinking LED Breadboard Circuit

Run the Blinking LED Breadboard Circuit MicroSim fullscreen

About This MicroSim

This is the first circuit almost every club builds, drawn on the board it is actually built on. Five parts, one loop: the 5 V rail, the output pin, a 220 ohm resistor, the LED, and the wire back to ground.

The circuit is solved rather than scripted. The 13.2 mA you see with the pin HIGH is what the solver computes from a 5 V supply, a 220 ohm resistor, and a red LED's 1.9 V forward drop -- not a number typed into the sim. Change the circuit and the number changes with it.

Two things are modelled on purpose.

The output pin is a switch, not a power supply. The PIN switch straddling the center channel connects the LED branch to the 5 V rail (HIGH) or leaves it open (LOW). The rails stay energized either way, because that is the truth: toggling a pin in code does not power down the board.

The loop must be closed. The Break the loop button rebuilds the circuit without the ground-return jumper at column 13. Everything else is still there -- supply, resistor, LED, output pin cycling away on its timer -- and the LED stays dark, drawing 0.0 mA. Current needs a path back, and a circuit with one wire missing is not a circuit at all. That is the single most common reason a student's first build does nothing.

The scope on the right plots LED current and LED voltage against time, so a slow blink interval draws a visibly wider square wave than a fast one.

How to Use

  • Press Start. The output pin begins cycling and the LED blinks.
  • Drag Blink interval from 100 ms to 2000 ms and watch the square wave on the scope stretch out.
  • Press Break the loop. Predict what the LED does before you look -- then press Reconnect the jumper.
  • Uncheck Auto blink and click the green PIN switch on the board to drive the pin by hand.
  • Reset restores the intact loop, a 500 ms interval, and auto blink.

Lesson Plan

Bloom level: Apply (L3) -- demonstrate

Learning objective: Given a breadboard, resistor, LED, and jumper wires, the learner demonstrates how they combine into a working blinking-light circuit.

Before the sim (10 min). Lay the four physical parts on the table and ask the group to arrange them into a loop on paper. Do not correct the wrong answers yet.

With the sim (15 min). Compare each paper layout against the board. Then run the Break the loop experiment as a prediction exercise -- ask for a show of hands on what the LED will do before anyone presses the button.

After the sim (20 min). Build it for real. A student who has already seen the broken-loop case debugs their own dark LED far faster, because "check that every wire is seated" is now something they have watched matter.

Check for understanding. Ask: "The pin is HIGH and the LED is dark. Name two things that could be wrong." A broken loop and a backwards LED are the two answers worth having -- and the second is why LED Anatomy comes next.

Embedding This MicroSim

Paste this into any page of the book, adjusting the relative path to docs/sims/ for the page's depth:

<iframe src="../../sims/blinking-led-breadboard-circuit/main.html" width="100%" height="602" scrolling="no"></iframe>

Specification

The full specification below is extracted from Chapter 16: Physical Computing and Electrical Safety Basics.

Type: microsim
**sim-id:** blinking-led-breadboard-circuit<br/>
**Library:** p5.js<br/>
**Status:** Specified<br/>
**Template:** https://github.com/dmccreary/microsims/tree/main/docs/sims/breadboard

Purpose: Show an animated, current-flow view of a complete blinking-LED circuit built on a real breadboard layout.

Bloom Taxonomy: Apply (L3)
Bloom Taxonomy Verb: demonstrate

Learning objective: Given a breadboard, resistor, LED, and jumper wires, the learner demonstrates how they combine into a working blinking-light circuit.

Visual elements: Realistic breadboard drawing with an LED, one resistor, two jumper wires, and animated current-flow dots moving along the completed loop whenever the circuit is closed and the simulated output pin is HIGH

Interactive controls: Slider for blink interval (100ms-2000ms); toggle switch simulating "output pin HIGH/LOW"; a "break the loop" button that disconnects one jumper wire to show the LED going dark

Default parameters: Blink interval 500ms, loop intact, output cycling automatically

Behavior: While the loop is intact, the LED brightens and current-flow dots animate whenever the output is HIGH; clicking "break the loop" removes one wire and the LED stays dark regardless of output state, reinforcing the closed-loop requirement

Implementation notes: p5.js canvas rendering breadboard geometry from a coordinate table; animated dots along a path array; `setInterval`-style timing using `millis()`

References