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Ohm's Law at the Bench: Picking the Resistor That Saves the LED
One equation does most of the arithmetic a maker ever needs from electronics, and it is three letters long. What makes it worth a rung of its own is that the three commonest beginner disasters — the LED that dies instantly, the resistor that cooks, the divider that sags under load — are all the same equation applied carelessly.
An LED is the sharpest example. It is not a resistor: past its forward voltage the current rises almost without limit, so connecting one directly across a supply destroys it in a fraction of a second. The resistor beside it is not a formality, it is the only thing deciding the current.
Every SIK circuit published here that lights an LED has one, and this is why.
초급
3 hours
안내
1
1
Size the resistor for an LED, and see why it is not optional
Size the resistor for an LED, and see why it is not optional
Jupyter 노트북 불러오는 중…
이 단계의 재료:
LED 키트1 개
저항 키트1 개필요한 도구:
브레드보드
계산기
멀티미터2
2
Check the resistor will survive the heat
Check the resistor will survive the heat
Jupyter 노트북 불러오는 중…
이 단계의 재료:
저항 키트1 개필요한 도구:
계산기멀티미터3
3
The divider that works until you connect something
The divider that works until you connect something
Jupyter 노트북 불러오는 중…
이 단계의 재료:
저항 키트1 개필요한 도구:
브레드보드멀티미터계산기4
4
Measure it, and find out what your parts really are
Measure it, and find out what your parts really are
Build the LED and its resistor on a breadboard, then measure: the supply, the voltage across the LED, and the voltage across the resistor. They should add up to the supply.
Then work out the current from the resistor's voltage and its measured resistance, and compare it with what you calculated. The LED's real forward voltage will not be exactly the table value — it varies by part, by colour bin, and with current — which is why the calculation is a starting point and the measurement is the answer.
This also demonstrates Kirchhoff's voltage law without naming it: around any loop, the voltages sum to zero. Once you have seen it on a meter it stops being an abstraction and becomes a tool for finding where a missing volt went.
이 단계의 재료:
LED 키트1 개저항 키트1 개필요한 도구:
브레드보드멀티미터
직류 전원 공급기관련 블루프린트
이 블루프린트들은 지식을 공유합니다 — 기술, 재료 또는 원리
CC0 퍼블릭 도메인
이 블루프린트는 CC0로 공개되었습니다. 어떤 목적으로든 자유롭게 복사, 수정, 배포 및 사용할 수 있습니다.
제품 구매를 통해 메이커를 지원하세요. 판매자가 설정한 메이커 커미션 을 받거나, 이 블루프린트의 새로운 반복을 만들어 연결로 포함시킬 수 있습니다.