Level 1 · Light · project 2 of 24 · 20 min · ●○○○○
Morse Code Messenger
A push button, an LED, and a secret code — send real messages with light.
new here? Start with First Light — one battery, one resistor, one LED. It teaches the loop, LED direction, and why the 220 Ω resistor matters.
What you need
- 1× 3×AA battery pack (4.5 V)
- 1× Solderless breadboard
- 3× Jumper wires
- 1× Yellow LED (5 mm) yellow flashes read best across a room
- 1× 220 Ω resistor
- 1× Push button (tactile)
you'll learn: Circuits are loops · Switches · LED polarity
Circuit map
The circuit you'll build, running on the Workbench right now — shown with the switch closed.
simulating…
If it doesn't work
The boring ways this circuit actually breaks — check these first before you unwire everything.
- LED never flashes. Flip the LED — long leg toward +. Then check the 220 Ω is in the lane, then that the button is really bridging.
- LED stays lit even without pressing. The button wires are on a pair that was already connected. Push buttons bridge DIAGONALLY — move one wire to the opposite corner.
- Button pressed, nothing happens. Same diagonal problem. If both wires enter contacts on the same side of the button, they were already joined and pressing does nothing.
- Nothing at all. AA pack switch first. Then trace + through the button, through the 220 Ω, through the LED, back to −.
- LED is dim. Wrong resistor. 220 Ω = red-red-brown. Anything bigger dims it fast.
What you're building
A signal lamp. Tap the button and the LED flashes exactly as long as you hold it — short taps and long holds. That's enough to send Morse code, the dot-and-dash alphabet that carried real messages across oceans for over a century. Ships still learn it.
The big idea: momentary switches
The slide switch from First Light stays wherever you leave it. A push button is different: springs inside connect the loop only while your finger is down. Electronics people call that momentary. Slide switches are for states (on/off); buttons are for events (taps, presses, knocks). Every game controller you've ever used is built on this difference.
Build it
- Push the button into the breadboard so it straddles the center groove.
- Wire the battery red (+) to one leg of the button.
- From the leg diagonally across the button, go through the 220 Ω resistor to the LED's long leg. (Diagonal legs are always on opposite sides of the button's internal switch — the safe choice.)
- LED short leg to battery black (−).
- Tap. Flash. You're on the air.
The current math is the same engineering as First Light: (4.5 − 2.0) V ÷ 220 Ω ≈ 11 mA — comfortable for the LED no matter how long you hold the button.
Send your first message
Dot = quick tap. Dash = hold about three times longer. Leave a little gap between letters.
| Letter | Code | Letter | Code | |
|---|---|---|---|---|
| S | · · · | O | — — — | |
| E | · | T | — | |
| H | · · · · | I | · · |
S O S (· · · — — — · · ·) is the famous one. Start there, then look up the rest of the alphabet and teach a friend — a code is only fun with two people.
🧠 Your challenge
No single right answer. That's the point.
- The button has four legs but only acts as one switch. Using the LED as your tester, figure out which pairs of legs are always connected and which pairs connect only when pressed. Draw what you think is inside.
- Set up a two-station telegraph: your button flashing a friend's LED a wire's-length away. How many wires do you actually need between stations?
- Invent your own 5-symbol code for messages you send most ("dinner!", "mom incoming"). What makes a code fast to send and hard to mix up?
For grown-ups: safety notes
- Battery-safe voltages throughout — nothing here can shock you.
- Long button holds are fine: the resistor keeps the LED at a safe current no matter how long you press.
- Don't flash SOS at actual ships or aircraft — it's a real distress signal and treated seriously.
Checked against
Keep building
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