simple led question blue led problems

Hi.
So im new to arduino and am just put a series of led in a circuit. I have a problem with the blue leds.
On their own they are fine. A blue or a pair of blues in series are fine, but as soon as i put in another colour, blues no longer light up while other colours do. I can’t figure out why, its like they are just skipped over. Their position in the series doesnt change anything, so its not like theres not enough current.
Thanks
Edit: so heres the circuit drawing and actual setup. It turns out this is parallel not series. Howver still cant figure out why the 2 blues dont light up unleass they are on their own. I’ve tried a number of configurations but the blues dont work with the other leds.

Here's the questions:

  • Why are you putting blue LEDs in series?
  • From what voltage are you powering them? With what resistors?
  • What does "put in another colour" mean?
  • Why have you not included a link to your circuit diagram (as an image link please, not an attachment)?
  • Do you believe we are psychic?

here's the answers:

  1. Because im new and part of being new is not knowing what to do. Im on page 30 of the book and it says you can extend this project by putting in leds and other components in parallel or series.
  2. 5V but it has nothing to with this as theirs enough power to power 4 leds.
  3. put in another colour means put in another color. In other words, I remove one of the blue LED's and replace with another colour (you know red, green, blue).
  4. I don't know where you expect me to get or make a circuit diagram. Like I said I'm new. Do you think im psychic. plus its simply 4 LED's in a series circuit.
    well if you're gonna be rude about it:
  5. why the hell aren't you

ahuss:
here's the answers:

  1. Because im new and part of being new is not knowing what to do. Im on page 30 of the book and it says you can extend this project by putting in leds and other components in parallel or series.
  2. 5V but it has nothing to with this as theirs enough power to power 4 leds.
  3. put in another colour means put in another color. In other words, I remove one of the blue LED's and replace with another colour (you know red, green, blue).
  4. I don't know where you expect me to get or make a circuit diagram. Like I said I'm new. Do you think im psychic. plus its simply 4 LED's in a series circuit.
    well if you're gonna be rude about it:
  5. why the hell aren't you
  1. I am sure your book (what book BTW?) tells you something about using a series resistor to use with any LED. Do this, please
  2. There may be enough POWER, but 5V is not enough VOLTAGE for several blue LED since these happen to have the highest forward voltage of all colors
  3. Explained by 2.
  4. Providing a circuit diagram for even this simple circuit would at least have answered whether you are using a series resistor and if you are really talking about SERIALLY connected LEDs. I understood from your original post that a red and a blue LED in series only light the red one. This can not be

Hi
Thanks for our reply, appreciate it.
The book i meant was the project book from the starter kit. I realised this should have been posted in another place.
if things can me moved around by a mod/admin would be great.

By series resistor do you mean two or more resistors connected together in a series.
Also yes you understood correctly i was saying that putting in a red(1 or more) and a blue led would result in the blue light turning off while the others would remain. This couldn’t have been something to do with the circuit not being a series as when I switched out that LED with other colours a red or green, these colour would light up. I tried another blue. Same thing.

Also could you recommend a tool for drawing these circuit diagrams. Thanks

ahuss:
2. 5V but it has nothing to with this as theirs enough power to power 4 leds.

This depends whether you are putting them in series or parallel, and how you are using the series resistors and whether - as I presume you would be - you are trying to control them from Arduino pins which require you to limit the current to 25 mA per pin if you do not wish to damage the Arduino.

ahuss:
3. put in another colour means put in another colour. In other words, I remove one of the blue LED's and replace with another colour (you know red, green, blue).

But you are (still) not properly describing to us how you are not connecting them.

ahuss:
4. I don't know where you expect me to get or make a circuit diagram. Like I said I'm new. Do you think im psychic. plus its simply 4 LED's in a series circuit.

As others have noted, LEDs in series will generally require more than 5V - notably if they are colours other than red. We suspect this is your problem, but you are not describing it well, this why the request for the circuit sketch.

ahuss:
well if you're gonna be rude about it:
5. why the hell aren't you

Well played!

ahuss:
The book I meant was the project book from the starter kit.

The trick here is that very few of us who answer here, actually purchased the starter kit with the book (except maybe for the guy that wrote it!). Most of us just use parts as we need them. I seem to recall a site where you can illegally download one such book, but in general rather than just referring to "the book", you should at the very least cite a link for it.

ahuss:
I realised this should have been posted in another place.

Perhaps, perhaps not.

ahuss:
if things can me moved around by a mod/admin would be great.

It can - but it does not matter that much.

ahuss:
By series resistor do you mean two or more resistors connected together in a series.

No, we mean the series resistor that is absolutely necessary for each LED, or series chain of such, to control the current they draw.

ahuss:
Also yes you understood correctly i was saying that putting in a red(1 or more) and a blue led would result in the blue light turning off while the others would remain. This couldn't have been something to do with the circuit not being a series as when I switched out that LED with other colours a red or green, these colour would light up. I tried another blue. Same thing.

Again, you need to properly describe how you are connecting these before it makes any sense.

ahuss:
Also could you recommend a tool for drawing these circuit diagrams. Thanks

Many would say "a pencil"!

While it is nice if you use a suitable piece of software and there are suggestions for such, just drawing it all reasonably neatly on a piece of white paper with necessary annotation, and taking a photograph using daylight but not in the sun, with a real camera from at least a metre away using zoom to ensure perfect focus, will do just fine.

@ahuss, you are new here, the guys are just giving you an initiation treat. You are welcome here.

First, it is not normal to put leds in series. Normally, one led with one resistor in series. The resistor value can vary, but 220 to 2000 ohms is a usable range.

Welcome, yes, but the point is that you must ask a question that makes sense to other than yourself. Ergo the common “Sorry, my crystal ball is out of service” comment. To communicate, you must describe things not from your present point of view, but that of someone who is not looking at the object in front of you; thus the persistent request for photographs.

It is a matter of context. Putting LEDs in series is the most common way of using them, since they individually operate at a low voltage. Virtually all of the luminaires in common use employ strings of many LEDs in series in order to accommodate to mains voltage.

The point here is of course, illuminating LEDs from the somewhat less than 5V provided by an Arduino output pin where a red LED has a threshold voltage of the order of 1.6 to 1.8 V but a blue or white (because white LEDs are simply blue LEDs with a fluorescent coating) will require something more like 3 V at minimum.

You may be able to run one of each type in series, you certainly can run two reds in series and for a series connection, if one does not light the other will not either. This is not what is described in the thread here, making me suspect that he is attempting to put them in parallel without the necessary separate resistors.

Ahuss your downfall appears to be putting the LEDs in series when you should be putting them in parallel. Each LED, regardless of colour should have a current limiting resistor. As Paul B said, the 5V provided by the Arduino cannot drive two Blue LEDs in series, it may work for red or green as the combined sum of their forward voltages would be less than what the Arduino can power - which means the LED lights. The closer you get to this 5V the less current will get to your LEDs and hence they do not light.

I’ve attached a schematic that might help. Note that the resistor values in the required configuration will need to limit the current to both of the LEDs such that they are less than the max current output of an Arduino pin. I think this is approx 40mA. Or alternatively you could use another Arduino pin but a resistor in series with this LED is still required.

Without seeing a schematic, we won’t know what you’re doing.

LED.JPG

Thanks for the answers everyone.
Ill find something for the circuit drawings.
lol initiation treat makes sense now.
And @ Paul B, so when you say max current of the arduino pins, I should be limiting the current when the pins are inputs to 25mA (although further down it says max is 40mA) and I assume the outpin current is always limited.
Lol sorry about the book thing. Its just thesimple book you get with the starter kit so I thought everyone had it. Guess not. It doesnt explain alot of things about the arduino and its pins as well as why it does things certain ways

Also maybe you're right that I could have put them in parallel, because I was able to power 2 blue LED's at the same time, but first I'll get back to remaking that circuit and then post back
Thanks again everyone, I appreciate your help

40 mA is the absolute maximum per pin for the Arduino.
25 mA would be in and around the recommended mark but your LED data sheet should mention a maximum current rating and this is what you should use so that you don't blow your LED (provided this number is less than the 40mA).

ahuss:
Ill find something for the circuit drawings.

Paper, pencil
Draw it out, take a picture of it and post it at a pic-hosting site and paste the link in your text.
That's as fancy as it has to get.

@Paul_B,
"It is a matter of context."
I agree. If taken out of context it may make no sense. I thought the context was hooking led(s) up to arduino's.

I could have written a book about how to power leds, if you need to power them from 120 volts, 240 volts, or 32,000 volts.

Thanks for the context clarification.

I suspect it is - but - he never actually explained what it is!

Or anything else for that matter. :astonished:

okay added attachments turns out it wa parallel but still the blues dont light

I’m not trying to hose you, but those pictures are shaky (switch to decaf.)
You can’t do four LEDs in parallel with one resistor, each LED needs its own resistor.
Since these are blues, 330_ohms (@ 5mA.)
Looks like an “exam” or something.

Dwg/Sch attached

parallel_4.jpg

In post # 6 it was already stated:
" Normally, one led with one resistor in series. "
Maybe the OP skipped over post #6.

lol you're right, been trying to get of caffeine a while now. plus cheap tablet camera

i read post #6, but as i said this is from the original question not something new.

and yes it was an old exam paper i had lying around.

so i cant put four leds in parallel without a resistor each, noted, but shouldnt that resistor limited the current to all of them.and i still dont understand why two reds light up and skip the middle.

"so i cant put four leds in parallel without a resistor each, noted, but shouldnt that resistor limited the current to all of them.and i still dont understand why two reds light up and skip the middle."

Your statement is half right, and half wrong.
"without a resistor for each", that indicates 4 resistors.
Then you speak of a single resistor again "but shouldnt that resistor limited the current to all of them"

Lets say a "LED unit" consists of an LED with a resistor in series. Now, if you want to hook up 4 "LED units", you can add each unit to the circuit.

Put another way. The resistor in one "LED unit" will not limit current in another LED unit.

"i still dont understand why two reds light up and skip the middle." Each led may draw more or less current/voltage than another led. So the ones drawing more current may light differently than the ones drawing less current. For example, if you get a litter of dogs, they don't all grow equally, and the runts get the short end of the stick. This should not be of much concern, if you put one resistor in series with each led. Sorta like putting each of the pups in his own pin, and providing adequate nourishment to each separately.

As we suspected from your initial post, you are attempting to put LEDs in parallel.

The problem with that is that LEDs have a "threshold voltage" which means to say that below this voltage they do not conduct, while as the threshold voltage is reached they not only conduct, but will conduct a lot of current with only a very little increase in voltage.

The threshold voltage for red LEDs is the lowest, then comes orange, green and blue-or-white (since white LEDs are actually blue with a fluorescent coating which is why the chip inside looks yellow). If you connect different colours in parallel, then the chip with the lowest threshold voltage - the red one - will conduct as much current as you provide to it before the voltage across the parallel combination can reach the threshold voltage of any other colour.

If you provide (through your resistor) enough current that you might expect to fully light all the LEDs, then your red LED will take it all and be damaged. And due to variations in individual manufacture, even LEDs of the same colour will not share the current equitably (unless they are all from the exact same manufacturing batch and even then there is a limitation).

That means that you must control each LED's current with its own individual resistor (or for higher power LEDs, a current-controlling circuit) in series. You may then connect a number of LED/ resistor pairs in parallel across a source if that source can provide the current needed (which for an Arduino pin should be no more than 25 or perhaps 30 mA).

If your source voltage is somewhat more than the total of their threshold voltages, then you can - and in fact should because it will be more efficient - put a number of LEDs in series and control the current to that single series string.