Students click breadboard holes to see the hidden strips, fix an LED whose legs share a strip, trace a loop strip by strip, straddle the gap and use the rails, build the circuit on a real breadboard and upload the blink, then place every part themselves.
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Students will be able to
I can say which breadboard holes are joined.
I can place parts so each leg is in a different strip.
I can build a circuit on a real breadboard and upload a sketch.
Timing
Predict and Try 7 min · Worked example 8 min · Vary 8 min · Real hardware 14 min · Practise and Make 8 min
Before class
The board treats the named pin as HIGH (the blink sketch's on moment) and shows a short circuit or missing resistor as a warning. Some breadboards split each rail in the middle: check yours and say so.
Uploading: Arduino IDE (install, admin rights) or Arduino Cloud Editor (browser plus the Create Agent, an account). Choose before the lesson and test one board on the school network. Tinkercad remains the no-kit route.
Kit per pair: Uno and USB cable, breadboard, a 220 Ω resistor, an LED, two jumper wires.
Running the lesson
Predict: show a real breadboard turned over (or a photo) after the reveal: the metal strips.
Find the mistake: ask a student to trace with a finger which holes are joined to c7.
Real hardware: nothing is plugged into USB until a partner has traced the loop.
The hard part (on purpose)
Students build what looks like the diagram, not what is joined. Before they plug in, have them trace the loop strip by strip with a finger.
When students get stuck
What you will see
A question to ask
The fix
An LED won't light on the real board.
Which strips are its legs in? Which way round is it?
Different strips, long leg towards the resistor.
A student thinks rows are joined.
Click a hole: which ones light up?
Columns of five.
Answers to the checks
one column: The LED's long leg is in c8 and its short leg in d8. The rest of the circuit is fine. The LED… It stays dark. c8 and d8 are in the same strip (column 8), so the strip joins its two legs and the current takes the easy path round the LED.
Look at column 8: Click a hole in column 8. Which holes light up?
a8 to e8: one strip. Both of the LED's legs are in it.
Fix it: Move the LED's short leg (−) so the LED lights.
With the short leg in column 9, where the GND wire is, the loop goes 13 → column 3 → resistor → column 8 → LED → column 9 → GND.
Strip by strip: Which holes are joined to a3? b3, c3, d3 and e3 Column 3's top strip: a3 to e3.
Find the mistake: Sam thinks this LED (long leg c7, short leg c8) is shorted out. It isn't. Click the line where Sam's reasoning first goes wrong. line 2 Line 2: rows aren't joined. c7 is in column 7's strip and c8 in column 8's, so the LED's legs are in different strips: the loop goes through it.
Across the gap: This LED straddles the gap (e7 and f7), but stays dark. Move the GND wire so it lights.
The GND wire was in column 7's top strip, joined to the LED's long leg. In the bottom strip (f7–j7) it meets the short leg.
On the rails: 5V and GND are on the top rails. Move the free ends of W3 and W4 so the LED lights.
W3 from column 5 to the + rail, W4 from column 10 to the − rail: 5V → resistor → LED → GND.
Which holes?: A resistor has one leg in a12 and the other in a16. Which holes are joined to the second leg? b16, c16, d16 and e16 Column 16's top strip.
A short: A wire goes from 5V straight into the same strip as a wire from GND. What happens? A short circuit: a huge current; unplug it at once 5V joined straight to GND has no resistance to limit the current.
build it from scratch: The wires to pin 13 and GND are in. Place the resistor and the LED so the LED lights safely.
Pin 13's strip → resistor → a middle strip → LED (long leg first) → GND's strip.
Solutions
One possible solution for each task. Other correct programs are fine.
Vary: the gap and the rails › Across the gap
Open task: any program that does what the step asks.
Vary: the gap and the rails › On the rails
Open task: any program that does what the step asks.
build it from scratch
Open task: any program that does what the step asks.
Stretch and support
Stretch: Put a second LED and resistor on pin 12, using the GND rail for both LEDs.
Support: A printed breadboard map with the strips shaded.
Exit ticket
An LED's legs are in b14 and e14. Will it light? Why?
No: both legs are in column 14's strip, so the current goes round it.
What each step is for
one column: Committing to what happens when both LED legs share a column tests the new move: legs in the same strip are joined to each other, so the current goes round the part.
Try: find the strips: Clicking holes shows the strips directly, which settles the prediction; then students fix the LED by moving one leg.
Worked example: trace the strips: Tracing the loop strip by strip models the move; Sam's 'rows are joined' is planted after the method.
Vary: the gap and the rails: Two more pieces of breadboard: a part can straddle the gap (its legs in two strips), and the rails carry power and GND along the board.
Build it for real: Building the same circuit on a real breadboard and uploading the blink sketch is the step from simulator to hardware; the strips are the first thing to check when it doesn't work.
which holes?: Reading connectivity without the board, including the gap and the rails.
build it from scratch: Placing every part from scattered positions puts the whole idea together: each part bridges two strips, and the loop runs from pin 13 back to GND.
Where it leads
Next: A small system (a brief, criteria, and tests on the boundary).