# Simple LED circuit is not working

This is my first circuit ever (!) and so I'm hoping that I'm just making an easy-to-spot rookie mistake. I am trying to power an Arduino Due with a 9V battery and then have the Due in turn power a red LED. No blinking. No sketchpad/C program flashed to the chip. Just straight up electricity:

When I connect the battery, several things happen:

1. There is a green power LED on the Due that lights up; and
2. Right next to it is an orange LED (on the Due itself) that blinks every few seconds (not sure what this LED is or what the blinking means, but providing that detail for good measure); and
3. The red LED on the breadboarrd does not light up

This is a 2V/15mA LED, and as you can see I'm powering it from the 5V power jack on the Due. So a 220 ohm resistor should be perfect for it (`R = (Vs - V) / I = (5V-2V) / .015A ~= 220 ohms`).

So, for the first time ever, I busted out my multimeter, set it to the voltage setting, and started testing the circuit. First I tested `Vin` and `GND` on the Due (that is, the connection between the battery and the Due), and the multimeter lit up and hovered (correctly) around 5V. So far so good. Next I tested the power and ground connections on the breadboard power rails (indicated in green above). Again, the multimeter reported a roughly 5V power supply. Then I tested the connection from the power rail to the row (purple in pic above) feeding power to the resistor, and to my surprise, the multimeter reports no power at those two purple locations.

My understanding was that the power rail will power the entire column its connected to (in my case, the left-most column), and then any rows connecting to a power rail/column will also be powered. So I'm not understanding why there's voltage on my power rail/column, but not on the wire connecting my power rail to the resistor. Any ideas?

### Update:

Here is my corrected circuit per initial feedback. Please note this is still not working, but I think I'm getting close:

• The LED is shorted out - both leads are connected together - as shown here Jun 10, 2015 at 15:34
• LED is connected directly to the 9V battery. It's not under Arduino control. No blinking here.
– user31481
Jul 19, 2017 at 12:11

What connects the resistor to the LED?

Absolutely nothing.

It's hard to work out which holes the LED is plugged into, but I think your current circuit looks something like this:

You need to connect that resistor and LED together.

Now your circuit looks like this:

Behind the 5 pins in that column with the ground wire there is a big chunk of metal connecting them all together. It's no different to if you'd taken the LED and twisted the pins together into one. There's no way the power can get up one and down the other when they are connected together like that. You need to separate them into different columns.

And this is how the (black) connections inside are laid out, and how your (red) electricity is flowing:

And here is how the circuit should look, using a program called Fritzing. It's a pretty basic design tool, but great for showing wiring.

You can see how the green highlighting shows the columns that are connected.

• Thanks @Majenko (+1) - please see my update a new pic. I did my best to follow your advice but the LED is still not lighting up. I think I'm closer but I'm still missing something. In that 2nd picture, you'll notice that I've placed the LED and the wire going back to the `GND` rail on the same row as the resistor's "cathode" end. Any ideas where I'm going awry now? Thanks again! Jun 10, 2015 at 14:51
• I have edited my answer to cover your edit. Jun 10, 2015 at 15:16
• I totally get it now, makes perfect sense! Thanks again! Jun 10, 2015 at 15:22
• Glad you have it :) I've added another picture and comment to my answer. You might like to check out the software "Fritzing" (free) which I used to draw it. It can be a big help when learning. Jun 10, 2015 at 15:26
• Oh,and your next exersize... move the +5V connection wire from the +5V pin on the Arduino and connect it to pin 13 instead - you'll then see the LED blinking at the same time as the one on the Arduino. Jun 10, 2015 at 15:32

It looks like you've got confused between columns and rows.

You are correct that the power rails run the length of the breadboard -- these are seen as the top and bottom pairs of rows in the diagram below (ignore the middle row). However, the rest of the board is connected up as separate columns. Each column is independent of its adjacent columns.

This means your red wire going from the power rail to the resistor is connected correctly. However, the other end of your resistor is currently going nowhere. It needs to be in the same column as the anode of your LED.

• Thanks @Peter R. Bloomfield (+1) - so I don't think it's that I'm misunderstanding how the breadboard is organized (as columns and rows), perhaps I'm so new to electricity that I'm just misunderstanding the very flow of power itself! Let's call the two rows that the resistor is "living on" the resistor anode row and resistor cathode row, respectively (although I understand resistors have no polarity). So you're saying that I have the resistor anode row wired correctly, meaning I am correctly powering the resistor from the power rail... Jun 10, 2015 at 14:39
• However, you are then saying that the resistor cathode row is "going nowhere". I would have expected the voltage/power coming into the resistor (via the anode row) to provide power to the resistor cathode row. Is this not the case?!? In any respect, how should I be wiring the resistor and the LED so that the circuit is correct? Perhaps once I see how it should look, everything will make sense to me. Thanks again! Jun 10, 2015 at 14:41
• Also @Peter R. Bloomfield please see my update and my comment underneath Majenko's answer - I have the same question for you! Jun 10, 2015 at 14:51
• @smeeb The line which your resistor anode is on is not connected to the line the resistor cathode is on (except by the resistor itself). That's vital because the power has to flow into a component and then out. If they were connected by the breadboard itself then virtually no power would go through the resistor (electricity always takes the path of least resistance). Jun 10, 2015 at 15:14
• @smeeb In your updated image, that's exactly the problem. Your LED anode and cathode are on the same column, so they're directly connected to each other by the breadboard. That means the electricity won't flow through your LED at all. The LED's anode and cathode need to be on different rows. Jun 10, 2015 at 15:15