Level 1 · Light · 20 min · ●○○○○
Morse Code Messenger
A push button, an LED, and a secret code — send real messages with light.
What you need
- 1× 3×AA battery pack (4.5 V) L1
- 1× Solderless breadboard L1
- 3× Jumper wires L1
- 1× Yellow LED (5 mm) yellow flashes read best across a room L1
- 1× 220 Ω resistor L1
- 1× Push button (tactile) L1
you'll learn: Circuits are loops · Switches · LED polarity
🔧 Open in Workbench — test this exact circuit virtually, then rewire it however you like.
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.