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Ohm's Law at the Bench: Picking the Resistor That Saves the LED
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23. Septemba 2026SE
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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.
Mwanzo
3 hours

Maagizo

1

Size the resistor for an LED, and see why it is not optional

Inapakia daftari la Jupyter…

Vifaa kwa hatua hii:

Kifurushi cha LEDKifurushi cha LED1 kipande
Seti ya vizuizi vya umemeSeti ya vizuizi vya umeme1 kipande

Zana zinazohitajika:

Bao la MajaribioBao la Majaribio
KikokotooKikokotoo
Kipima-umeme cha aina nyingiKipima-umeme cha aina nyingi
2

Check the resistor will survive the heat

Inapakia daftari la Jupyter…

Vifaa kwa hatua hii:

Seti ya vizuizi vya umemeSeti ya vizuizi vya umeme1 kipande

Zana zinazohitajika:

KikokotooKikokotoo
Kipima-umeme cha aina nyingiKipima-umeme cha aina nyingi
3

The divider that works until you connect something

Inapakia daftari la Jupyter…

Vifaa kwa hatua hii:

Seti ya vizuizi vya umemeSeti ya vizuizi vya umeme1 kipande

Zana zinazohitajika:

Bao la MajaribioBao la Majaribio
Kipima-umeme cha aina nyingiKipima-umeme cha aina nyingi
KikokotooKikokotoo
4

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.

Vifaa kwa hatua hii:

Kifurushi cha LEDKifurushi cha LED1 kipande
Seti ya vizuizi vya umemeSeti ya vizuizi vya umeme1 kipande

Zana zinazohitajika:

Bao la MajaribioBao la Majaribio
Kipima-umeme cha aina nyingiKipima-umeme cha aina nyingi
Chanzo cha umeme cha mezaChanzo cha umeme cha meza

Vifaa

2

Zana Zinazohitajika

4

Blueprint zinazohusiana

Blueprint hizi zinashiriki maarifa — mbinu, vifaa au kanuni

Driving an RGB LED — SIK Circuit 3

Driving an RGB LED — SIK Circuit 3

na EdFI

Dijitali

93
0
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0
0
0
Driving Multiple LEDs — SIK Circuit 4

Driving Multiple LEDs — SIK Circuit 4

na EdFI

Dijitali

91
0
0
0
0
0
Wheatstone Bridge

Wheatstone Bridge

na EdFI

TEKNOLOJIA

38
0
0
0
0
0

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