BUILD CARD · EASY
LED Reverse-Polarity Test
Reverse the protected LED and observe that polarity controls whether it can light.
- Time
- 10 min
- Age
- 8+
- Pieces
- 7
- Board
- 10×7
- Build and check a 10×7 snap-grid circuit from a visual diagram.
- A reverse-connected LED blocks normal current even when the rest of the circuit is complete.
02 / PARTS CHECK
Parts list
- 1×8-snap wireconnector
- 1×3-snap wireconnector
- 1×2-snap wireconnector
- 1×White LEDsemiconductor
- 1×100 Ω resistorresistor
- 1×Slide switchswitch
- 1×3V two-cell battery holderpower
03 / ASSEMBLY
How to build the circuit
- 1
Disconnect the battery and clear the base grid before placing any part.
- 2
Match the final diagram one grid position at a time, placing connecting wires and lower layers first.
- 3
Check the direction of every LED, diode, transistor, battery, and other terminal-sensitive part.
- 4
Press every shared snap firmly, check that no wire shorts the battery, then connect power last.
04 / FIELD NOTES
How it works
The reversed LED blocks normal current even though the rest of the loop is complete.
The resistor remains in place so the comparison is controlled and safe.
Return to the forward-polarity drawing to make the LED light.
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05 / TEST
Test and expected result
- What to do
- Close the switch briefly with the protected LED reversed, then compare it with the forward circuit.
- What to expect
- The reversed LED stays off because it blocks normal current in that direction.
06 / SAFETY
Build smart
- Test only with the 3V battery holder.
- Keep the 100 Ω resistor in series.
- Open the switch before rotating the LED.
07 / TROUBLESHOOTING
If it does not work
- If the LED lights, compare its polarity marks with the drawing.
- Use the same batteries and resistor as the forward test.
- Do not remove the resistor.
08 / FREQUENTLY ASKED QUESTIONS
Questions about this circuit
What is the main idea behind this circuit?
A reverse-connected LED blocks normal current even when the rest of the circuit is complete.
What should I check first if it does not work?
If the LED lights, compare its polarity marks with the drawing.
09 / RELATED BUILDS
Try a similar circuit
Continue with another build that shares the same components, ideas, or difficulty.
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