I know next to nothing about electric engineering, so I got the Arduino Uno R3 and a bunch of LEDs to play around with and hopefully learn something. I have no idea about the proper terminology or anything here, so bear with me ...  When I connect an LED to a normal pin, it works fine. When I connect it to 5V or 3.3V with a 220 ohm, it works fine. Without the resistor, the LED gets cooked. My question is, why does it work with the digitals without resistance and not the 3.3V or 5V? Are they hooked up to onboard resistors? What is their output?  And finally, where can I learn more about my shiny new microcontroller without diagrams that I can't make head or tail of?  Edit: I think this is different from the related question I noted in my comment, but tell me if I should remove it anyway.
108780
I'm just trying out Arduino Uno for the first time with 2 blinking LEDs on a breadboard. All the tutorials on the Internet seem to use a resistor. I do know the function of resistors, but does it really matter here? These LEDs are working just fine without a resistor.
58416
I'm trying to make an RGB color mixer. LED strip runs on 0.5-2A. It has internal resistors. LED Strip needs 5v, has one pin for that, one for red, one for green, and one for blue. Each LED module that you can cut off was about an inch an a half, actually a little less, and there's 5.5' of the strip, I think there's around 40 LEDs in the strip. I found this video online, but this is the exact LED strip I got. .         &ndash; Schematic created using   Original schematic.  I will be using a total of 6 volts. i saw a video where a guy made a PWM circuit, , and it looked something like this.          555-based PWM control.          Tidied-up schematic.  I meant for the threshold to connect to the trigger, but I couldn't get it to. I'm confused on how to pick my resistors, my pot, and my capacitor, because in a different video, it said something like 1.44/(R1+R2+R2)*C1=Frequency. I assume frequency is how fast the LED flickers? In this schematic, there's 2 capacitors, which do I use in the equation? Does higher frequency mean faster flickering? How fast would be too fast for the naked eye? How do I control which I way I turn the pot to make the lights brighter. And how do I know how much current is coming out of the the output? How can I control that so it doesn't burn out my LED?
28697
I have the following circuit, where I put R52 = R53 = 2700 Ohms :    Triggering levels are of 1V and 2V approximately according to my computations, that is okay according to the following figure showing input in green and output in blue :    But what I find really strange is that the maximum voltage output is around 3.3V and not at 5V. How would you explain that ? And last detail : how would you explain that the output is not exactly at 0V when the input is high?  Thank you very much for your help.
15855
It appears most people drive relays through a transistor rather than directly from a digital output pin on an Arduino.  I had wired the output pin directly to my relay before realizing this and it worked fine.  What's the transistor for?    Is it to protect the output pin from exceeding the max current if the relay coil has too low a resistance?  Or, is it to conserve energy taking advantage of the common emitter amplification?  To produce less heat perhaps?
69660
I have some "NDV rev1.1 4248 back lights" from a television.   There is a print that sais "94V" on the strip, and on the wire supplying the strips it said "96V".   Every strip has 9x buttons which have 3 LED's in them. So i devided 94 by 9 and figured that every button should have 10.4V roughly, which makes sense, because a white LED is normally 3.5 volts.  I have a 12v Lithium battery which measured 11.1V so i tested one of the LED's with it and it lasted less than one second.   Are the LED's are rated for 10.4V roughly and not more?
81021
I have some experience with highfrequency circuit analysys. However I am a newbie in PCB design. I am analysing this circuit:  (starts on page 36) and regularly see things like "OMIT" for headerpins or components like resistors or so.  e.g.:   p41 (6/6): the boxheader(?) on the left. P40 (5/6): R48 on the dev board are two small surfaces with some soldering on it but no component apparently. I can hardly see myself (de)soldering resistors on my new dev board...   Why is this being mentionned? What do the people who made the PCB mean by this?  I mean if this part has to be omitted, why did they even place it on the PCB?  Thx
76286
I'm trying to wire up 6 RGB LEDs in parallel, all controlled from a single source (well, three sources, one for each colour). The LEDs came supplied with resistors to limit the current of 270 Ohm for a 5v supply.  The problem is, 6 LEDs x 3 colours = 18 resistors, which is a lot, and means I need a much bigger board and a lot more soldering.  So, can I instead wire the LEDs in parallel with each other, with a single resistor protecting all six? (3 resistors in total, one for each colour). How do I calculate the value of that resistor?  More details:  The LEDs are being driven from a  to supply a bit of current, which is in turn controlled by a Netduino providing a PWM signal on the three channels.  . If I've correctly understood the data sheet they want 20mA of current, and forward voltages of 2, 3, 3 volts (for R,G and B respectively?). The supplied resistors were all 270 Ohm, so the channels may not be balanced quite right.  For extra credit: I'm only using 3 of the transistors in my driver chip, which has 8 in total. could I wire the PWM from the netduino to a second trio of transistors, and split the LEDs into two groups of three? Is it worth the effort?  PS I don't have any diagramming tools to hand, but I can provide a diagram (drawn in paint) if it would help clarify my question. (see also )
67441
Background I am building a scale RC helicopter and ordered a bunch of 3mm LEDs to give it some nice navigation and strobe lights which I plan to drive with an Arduino Nano. Problem is that I goofed and didn't notice that the LEDs are 12v until they arrived.  I know that the Arduino Nano can accept 12V on pin 30, but I think the voltage output on any of the &quot;D&quot; or &quot;A&quot; pins is always 5v (correct??). Question If the voltage output of the Arduino pins is 5v, then how can I drive the 12v LEDs using the Arduino, or is it impossible?
49071
So I'm trying to power 2 of these  together in series. I know that I have to add the voltage of the two lights together and get a resistor that restricts the power to that level. I have a 9V battery and the lights are 3V each. I brand new to all of this, and understand almost nothing, so any help would be appreciated. Can someone help me choose the correct resistor (And how to identify that resistor with the color branding thing) so two of those lights listed above can be wired in series? Thanks!
53033
This may be a stupid question, but I have searched online for a little bit and can't seem to find my answer. I am working on a circuit board that uses buttons that i've never seen before. These buttons just have a metal lead around them and an LED in the middle (for lighting up the button I'd assume) but how does a button like this even work? I've attached some pictures to show you what i mean.    this is the back of the push buttons from the device
22457
To power my microcontroller (ATmega8), I am using a ~5.4V voltage source. I want to ensure that I don't accidentally connect the voltage source in reverse, and figured a diode would be a nice way to accomplish this as from what I have learned so far, a diode allows current to flow in one direction, and blocks it in the other.  But what I also learned is that diodes create drops in voltage. I have a few of the typical diodes (1N4001, 1N4148, etc.), and would like to use them to achieve the aforementioned result without dropping the voltage as it would be too low to power the IC.  My question is, is there any way to do this with a diode? Or do I need some other component (if so, what would you recommend)?
107952
In the link below, this circuit I found is what I needed. Only the length of the pulse and the delay are not what I want.  When I want just 0.5sec before pin 3 is up and the pulse duration I want is also 0.5sec, can someone tell me how big my resistors and capacitors must be? Or can someone tell me how I can calculate this?  My source power is 16 Volts I have already found 555 timers that can operate with 16 Volts, so thats not the problem.  When someone has another idea with two 555-timers, or something else that does the same, it's also OK.  Thanks
7517
I have an adjustable 24VDC power supply.  I have 1W LEDs that I was planning on stringing 7 or 8 in series to get approximately 24V across all of them together. They are rated 3.3-3.8V each. Do I need a resistor in series to maintain current? I was thinking so since a lit LED is basically a short? I can't find an answer to what it is really needed for, just that most people say to put a resistor in series to 'limit current'...  if so, it would be a small resistor, around 2 or 3 ohm?
105310
I came into Electronics through Arduino, so pardon me if my knowledge about non-Arduino circuits is somewhat silly. I am preparing a small electronics project for my school with LDRs to detect light levels. With, an Arduino I could easily detect light levels and when they go down a threshold, I turn on a relay.   But, I wanted to make this without an Arduino, so I though of using an LM339 Comparator. I connected pin 3 of IC to Vcc and pin 12 to Ground. Pin 4 has an input lower than the input on pin 5 which receives input from Vcc. Lastly, I had the output 1 from pin 2 connected to an LED.  This circuit is only to test the comparator. If it works I am going to change the reference voltage and in place of the LED place a transistor. Here is a quick circuit Diagram I created:  But, the LED does not glow. Even if I switch the inupts, the LED does not glow. I tested this in circuits.io, the online simulator. It works perfect there. But, the problem persists on the breadboard.  How do I get the LED to glow in my circuit on the bench?  UPDATE: I just got the LED glowing with the help of Raj, but how can I connect the base of a transistor in place of the LED.
22599
Let us suppose we have an LED with the allowed voltage range of 1.5V to 4.5V and we gave it somewhat 12V. Now we know that the LED will instantly stop forever. But I want to know what will happen to the material (the semiconductor, etc) when this happens.
112307
Are pull-up/down resistors (whether internal or external) only needed for MCU INPUT pins? In contrast, an MCU pin configured as an OUTPUT "knows what level it's at" because it does the driving - a "floating" MCU OUTPUT pin tied to some input of another circuit doesn't make sense, because the state of the MCU pin can only be high or low... do I have this right? Now, upon MCU bootup or failure, it may be beneficial to have a pull-up/down tied to this "MCU output to IC input" line to ensure that the input to some IC is never floating.  Maybe I just answered my own question here... pull-up/down resistors can be used on both input and output pins, depending on application?
9516
I would like to know how can i add a safety switch with an LED indicator to a circuit , so that if the safety switch is on then the LED lights , and when i want to use the device , all what i have to do is to press the normally-open switch.   I have attached this schematic and im not sure if it will work correctly  ,as i am a very beginner in electronics   Thanks