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How to solder LED's to PCB with resistor? Answered

I am trying my first electronics project and found this an ideal project to just apply the basics.
I basically have a PCB on which I have want to solder LEDs (and provide 270k ohm resistor protection). I just learnt basic soldering stuff and soldered a LED and a resistor on the PCB, but don't have clue about the connection to be made for the circuit. Neither does the above project which I surmised as a good starting point mention about any circuit diagram, and further its connections with the Arduino.
Can somebody point out how do I connect a simple LED and resistor in a circuit? [Current image attached]
And in the context of the above project that I am following, how do I create the circuit and connect with the Arduino?




Best Answer 5 years ago

You know the above pic is the back side of the board
the component wires soldered through are on the Other side !

Have a look here.


@iceng: The blue line that you see has the LED components soldered, and the other soldered components line above the blue line are resistors. I'll attach the image of the front side as well here.


The SMD components are soldered to copper pads
by applying a hot iron to the copper pad, component edge and
applying solder at the same time.

Keep in mind the LED has polarity, orientation makes a difference.
One way Works !  The other way Fails.

The Resistor orientation does not matter.



@iceng: I did take care about the cathode/anode polarity of the LEDs. Now only if I knew how to connect the LED and resistors in a circuit and specifically for this project (Link: https://www.instructables.com/id/Arduino-controlled-Interactive-wallpiece/) would I be able to proceed.

As shown in the picture above, the components are already soldered (and polarities are marked for later use), but how is a LED and resistor connected physically on the board? Currently, both of them are two separate soldered components on the board.
How is the power supply given usually?
How is the ground given usually?

Oh! So the solder pads of towards the anode of the LED are connected to the Resistor on one side. That clear some doubts. Thanks.

You are Correct ...

Now ... I hope you know how to click on the Best  Answer.

The resistor you mention should be 270R (two hundred and seventy ohms - red, violet, brown) not 270k (two hundred and seventy thousand ohms - red, violet, yellow). 

HERE is a diagram which shows how the LED and resistor should be connected.  It would also work if the resistor and LED were swapped over.
(This is for a Picaxe; a different microcontroller so the code won't work for your Arduino, but the wiring is the same.)

@AndyGadget: Doh! I have a 270k resistor (Red, Violet, Yellow) and have already soldered these here. Would this also work somehow or should I change these now?

With 270K the current through the LED will be too small to make it light at all.
Do you have any other resistors?  Anything from 150R (bright) to 2K7 or so (dim) would do the trick. 
The Instructable you link really does not give very much detail on how they made it.  When I get time a bit later I'll track down something which does the same thing but is better documented.

I don't think I have resistors available with me. I'll just go to a nearby shop and buy this stuff (270 ohm resistor) and a new PCB as well it seems.

Quote: "The Instructable you link really does not give very much detail on how they made it. When I get time a bit later I'll track down something which does the same thing but is better documented."

Thanks. That would be really helpful.

Have a look at THIS really simple project which uses one LED on pin 13 of the Arduino.  It's pretty obvious from the code (sketch) and the photos how you would extend this to more LEDs.

@AndyGadget: This was the first thing I did when I bought Arduino. However, what I am asking is about these connections on the PCB. https://www.instructables.com/files/deriv/FPQ/PHGL/H3DC0EI8/FPQPHGLH3DC0EI8.LARGE.jpg

In the above image, the connections have been done to connect different LEDs and resistors, and that is what I am not able to figure out.
Although that first simple LED blink example does work, that does not tell how to include a resistor in between connection of LEDs.

In my case, I have 9 such LEDs and resistors. I am also not sure if all these LEDs have to be connected to separate pins or all of these LEDs have to connected in a circuit and then only on 1 pin of Arduino is to be used.

Probably the answer to the "____" questions in the following steps would make it much more clear.
1) Solder an LED and a resistor on PCB.
3) Take a jumper wire, and connect the anode of the LED to one end of the resistor on the PCB. The other side of the resistor which is not connected by jumper wire has to be given power supply from Arduino. Connect this to the Arduino by ______ .
3) The cathode side of the LED has to connected to Ground. Connect this to the Arduino Ground by ________ .

Yes, you will need to replace the 270K resistors with 270 Ohm resistors. If you leave the 270K resistors in, you would need over 5000V to get enough current through the LEDs, which is obviously no good.

How many LEDs are you working with? Do you want all of them controlled from a single Arduino pin?

You will want to have the anode connected to one of the arduino pins and the cathode connected to the resistor and the other end of the resistor connected to ground. When the arduino pin is set to high the LED will light. Just look at the arduino pin as the positive lead of a power source. If you plan to run more then 1 LED off a single pin you have to be careful about the power being drawn through the pin. The arduino can only support 5V @ a max of 500mA when powered off USB. So there is a limit to the number of LEDs you can connect and then you run into having to arrange the LEDs and resistors in a series parallel array in order to run it off a single pin. Have a look at this LED calc for a good diagram of how to wire all your LEDs to a power source.

@mpilchfamily: I am working with 9 LEDs and 9 resistors (as I saw in this project how the each LED has a resistor along with it : https://www.instructables.com/id/Arduino-controlled-Interactive-wallpiece/)

I have posted some more images above, and my circuit basically looks like a 3x3 matrix where each matrix point has a LED and a resistor. As in the above project, I was looking to make each of these matrix points sensitive to touch. Though, I did get the answer about how to connect LED and resistor together, but could you post some more details on how connect all the LEDs, resistors together on PCB as well as with Arduino, so that I get the touch functionality as in the above project. For now, I am kind of stymied with the lack of detail here: https://www.instructables.com/id/Arduino-controlled-Interactive-wallpiece/

Are you asking how to physically connect the pads on the PCB so that the LED is connected to the resistor?

@bwrussell: I have added some images to @iceng reply above. I have already soldered LED and resistor components to the PCB above. However, what I am looking for here is how to physically connect the LED and resistors together on the PCB?
Project that I am following to build something: https://www.instructables.com/id/Arduino-controlled-Interactive-wallpiece/