# Help with the most basic LED circuit

#### JSR

Aug 3, 2023
5
Just trying to get an LED to light up on my breadboard (I am out of practice). Have built this circuit as pictured below (yes, a lot more wires than necessary). LED polarity is understood, and the small side (cathode) is connected to negative, and the larger sider (anode) is connect to positive.

The resistor is brand new 330Ohm pulled from a pack of others.

Power Supply is set to 9V and is showing 20mA.

Swapping the resistor, LED, and LED polarity changes nothing...

Did some simple ohms law math and probed with a multimeter to check expected values...all good.

What is wrong here?

Apr 21, 2011
137
Your power supply is indicating something between 20 and 29.999 milliamps.

Your power supply indication will not have perfect accuracy

A standard red LED will have a voltage drop of something around 1.6 to 2.0 Volts IIRC. This means that the resistor will have somewhere around 7.5 Volts across it

Your resistor looks to be accurate to 1%

Probe around with a digital multi-meter on DC volts range to get a better understanding of what is happening

#### JSR

Aug 3, 2023
5
Your power supply is indicating something between 20 and 29.999 milliamps.

Your power supply indication will not have perfect accuracy

A standard red LED will have a voltage drop of something around 1.6 to 2.0 Volts IIRC. This means that the resistor will have somewhere around 7.5 Volts across it

Your resistor looks to be accurate to 1%

Probe around with a digital multi-meter on DC volts range to get a better understanding of what is happening
That was helpful. I had a poor understanding of how the breadboard works; each point in a row is connected to all others... The way I set it up allowed the current to either exit the circuit, or go through the LED (parallel). Naturally, current wants to travel through the path of least resistance and the LED was bypassed. Just had to move things across 2 rows (in series).

Apr 21, 2011
137
Yes - the breadboard error was staring me in the face, but I still failed to see it.

Glad you worked that out for yourself.

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