Step 2: The LED

LEDs come in different sizes, brightnesses, voltages, colors and beam patterns, but the selection at Radioshack is pretty small and so I just picked up a couple different LEDs from what they had in a few different brightnesses and voltages. I kept close track of what LED was what voltage because I didn't want to accidentally send too much current through one of the low voltage LEDs.

The first thing I did with the LEDs was figure out which wire (its called an electrode) was positive and which was negative. Generally speaking the longer wire is the positive electrode and the shorter wire is the negative electrode.

You can also take a look inside the LED itself and see whats going on. The smaller of the metal pieces inside the LED connects to the positive electrode and the bigger one is the negative electrode (see picture below). But be warned - in the LEDs I picked up I didn't always find this to be true and some of the LEDs had the longer electrode on the negative when it should be on the positive. Go figure - its OK though, if it didn't light up I just flipped it around.

Once I knew what was positive and what was negative I just had to remember what the voltage of each LED was.

All my LEDs recommended 20mA of current. 20mA is standard for most LEDs.

<p>&quot;Once I knew that I needed a resistor of 140 ohms to get the correct amount of voltage to the LED&quot;</p><p>I think you mean to say that the resistor ensures that the <strong>CURRENT</strong> flowing through the circuit does not exceed LED's <strong>CURRENT</strong> rating of 20 mA. In your previous step...if you had an LED rated at 1.5 volts and you used a 1.5 volt battery WITHOUT a resistor, your applied voltage would be perfect but you would burn out the LED since the current flowing through it would be extremely large.</p>
<p>I understood your post and like to ask you something:</p><p>If ideally we had a 1.7v input, a 1.7v led that consumes 20ma, which resistor you would need to securely feed the led?</p>
<p>I understood your post and like to ask you something:</p><p>If ideally we had a 1.7v input, a 1.7v led that consumes 20ma, which resistor you would need to securely feed the led?</p>
<p>I thought that the LED itself can control the current passed through it when the applied voltage doesn't exceed its forward voltage? My teacher told me resistor only needed when the applied voltage exceed the forward voltage of the LED.</p>
<p>Hi... My sons Halloween costume has led lights on the chest that don't work. The board seems to be chipped. It has 8 blinking blue led lights powered by three 1.5v lr44 batteries. What can i use to supply power to the led lights. I attached a picture of the circuit board. Also, I attached a picture of the costume, the chest part is the one that's not lighting up. Thank you.</p><div><br><br></div>
<p>The black bit on the circuit board is a chip-on-board ic. It probably controlled the blinking of the leds. I am guessing it is probably busted from the board breaking. What I would do is remove the circuit board and replace it with a resistor. The leds will not blink anymore but they will light up.</p>
<p>If you want it blinking you could also replace that led with a blinking led. But it will blink independently of the other leds</p>
<p>Right, complete novice, so be gentle lol</p><p>Conflicting stories? I've read you don't need resistors, then you do, even a 5.1 Zenner diode was mentioned, don't run em in series etc. etc. </p><p>I have 2 flashing Red LEDs &amp; I want to run em off a 9v battery.......</p><p>Do you run em in series or parallel?</p><p>Do I need a single resistor or a resistor for each of the LEDs, if so, what resistors?</p><p>Regards</p><p>Tony</p>
<p>How can I connect more than 1 LED to a single switch with 3 toggles on the bottom? I know how to connect 1 LED, but I need to connect multiple ones!</p>
<p>Hi am a beginner with electronics and im wanting to make a series circuit using 2 red LEDs ( 5mm 1.85 v) and 1 white LED (5mm 3.3v). i have 2 types of resistor 1 180R and 1 220R. My power supply is a 9V battery. </p><p>My question is which resistor goes with which led?</p>
<p>R = (V1 - V2) / I</p><p>R=(9-( (2x1.85) + 3.3)/0.02 = 100 ohm</p><p>you need 100 or a bit higher. I am a bit rusty however.</p><p>see step 6 in this tutorial.</p>
<p>Totally the level I'm at. Thanks for the tutorial</p>
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<p>Well...keep moving on..</p>
<p>Can I use 5mm LED with 1V 1A load?</p>
<p>It will only work if your led's forward voltage is around 1v. Most leds are not. see the attached chart for different color led forward voltages.</p><p></p><p> You want to provide the voltage where the led color you are using passes the 20mA line (or whatever forward current is specified in the datasheet) </p>
<p>You can use whatever size, voltage rating, and current rating you desire. All you need to remember is to make resistor changes according to voltage supplied, voltage required, and current required.</p>
<p>In your calculation, where did you get .02A?</p><p>I plan on making some circuits with LED's and 12v 1000ma and 2000ma power supplies.</p>
<p>Most leds run at optimally at 20 milliamps (.02A). This is called the forward current on the led datasheet if you have it.</p>
<p>Great beginners guide!</p>
I have 8mm white leds to use in different projects but I don't know what resistors to use for the same? plz help me out?
I have a 60 volts led driver and 4 smd 12 volts 10 watts led.plz would u tell me need any register....<br>
<p>Thanks for this tutorial :)</p>
<p>The only other suggestion I might make is to use a voltage regulator (triple lead IC like device) that will keep your voltage relatively constant, and avoid resistor mis-identification problems. <br><br>You can eliminate the resistor and go forward safely. They come in values in the range you need for this. They have a range of input voltages, and will put out a steady voltage (some can be had that are variable for more money). I stick with fixed values.</p>
<p>Any regulator IC (fixed or variable) can be used as a variable voltage regulator by varying the voltage at the reference pin with a potentiometer. Use a parallel resistor to limit maximum excursion. The resistor values will (similar to the 'ible) vary according to voltage/current requirements for the particular IC in question. If you acquire the spec sheet for the IC you intend to use, there will almost always be a variable voltage output circuit somewhere on the page.</p>
<p>?? If I have a 3 terminal fixed voltage regulator, how do I make that adjustable? There is no Vref pin. </p>
<p>The 'ground' pin is used for Vref. The regulated output voltage will be normal regulated output voltage + Vref voltage. So, for example, if you have an LM??05 and your 'ground pin' floats at 3V, then your true regulated output voltage will be 5V + 3V = 8V.</p>
<p>I'm trying to figure out why different color LEDs won't light up when i add two together onto one battery&hellip;?? i'm betting it has something to do with the amount of power needed, but would like to know if that is correct.</p>
Using this instructable I made an led that will run off an 18v battery.<br>http://m.instructables.com/id/Kayak-LED-light/
Very nice.....Thank you very much.
<p>What would cause my LED to take a while to reach full brightness?</p>
<p>So nice... Needs more such help....</p>
<p>Thank you very much for doing this tutorial especially in plain english. I have 2 LED lights that I need to fix, I have broken it down to the actual switch. So I found the exact same switches at Radio Shack. Now I need to get up the nerve to remove the existing switches and replace with the new ones. The wires are so tiny I find it hard to strip them with out cutting into some wires. Do you have an easier way to do this.</p><p>I would really like to keep these solar lights going for the a long time. I like to see them all lit up when I drive up the road.</p><p>Again thank you for this tutorial is was very good. I believe I have to join Pro to be able to download it to my computer so I can reference back to it when I need to.</p><p>Glenda</p>
Very informative , I liked iy.
<p>The link below calculates LED resistor values for series or parallel arrays of any amount, color, and desired voltage. </p><p><a href="http://led.linear1.org/led.wiz" rel="nofollow">http://led.linear1.org/led.wiz</a></p>
<p>I was just about to post this link. I've been using it for years, such a great source.</p>
<p>Nice to see a real close up of the insides of one. :)</p>
<p>i liked the explanation of the wiring system rely helpfull </p>
<p>Step 6 got me thinking about wiring batteries in parallel. If I wanted to go longer between replacing batteries how could I get 4.5V from AA batteries?</p><p>For example, wiring six 1.5v batteries. 3 in series wired to 3 in parallel. </p>
<p>Nice instructable! Playing with LEDs is one of my favorite activities. I like the fact that you paid attention to voltage and current ratings - good advice for the beginners. One thing to note: you didn't use blue or white LEDs; people that do choose to play with these might use a little caution - they tend to be more sensitive to over-current and static electricity. It's a bummer to burn out a $5 LED right off the bat...</p>
<p>If you intend to crank as much light as possible out of a LED, (without burning it) you should probably pulse it and limit the temperature.</p><p>For regular signal LED's, it's not so important, but the optimal driving scheme is a current source. Without aktive components (transistor and Zehner diode), a current source is done by a high voltage and a high impedance(high resistor).</p><p>This way, it isn't that important, what the voltage of the LED is. With a active current source, it even doesn't matter if you have multiple LED's in series, as long as the supply voltage is high enough.</p>
<p>Thank you so much for your very good Instructable on LEDs!<br><br>I need to build a large array of IR emitter LEDs to light my yard at night and use a CCD camera to catch a jerk who's been Night Golfing in my yard. I have a collection of about 15 golf balls he's left behind Good ones, Titlist and Nike, mostly. I may start selling them on the Internet..... (This reminds me of &quot;Mitch Cumstein&quot; from Caddyshack!)<br><br>I plan to get a perfboard and solder it up, using your information and a nice adequate power supply. I'll have to calculate the value of the total load at operation levels, so as not to over drive them, and burn them out early... I plan a white reflector behind the array as my house is white and it would camouflage it from being seen at night. They won't t see the IR anyhow, only the CCD camera can.<br><br>One place you CAN get <strong><em>lots of good stuff</em></strong> (<u>I DO NOT WORK THERE OR HAVE TIES WITH THEM</u>) is a place I have bought the odd hard to find part from is a company in Miami called Dalbani Electronics. They have the run of the mill stuff too! They can get almost ANYTHING. And their prices are NOT astronomical, and are way more reasonable than at ShadyoRack. (I used to work for them, and won't buy there ever again.) I went by to find the price of a 357 button cell for a TI-30XA calculator. They sell for $5.99 for ONE. I found a five pack at Dollar General... Mercury Free, $1.00 for five.... Never pay retail if you can help it. For the two I needed, I could have bought a new calculator....</p>
<p>Some other alternate sources for electronic components: MCM Electronics, Jameco Electronics, Mouser Electronics. I have purchased supplies from all three of these sources over the past 40 years and find them all equally reputable.</p>
<p>I frequently buy at Tayda Electronics</p>
<p>I dig it... well done. I'm going to share to a group that likes to build models of space ships, as I often hear people ask how someone lit up a kit... </p>
GrinninSam questions, &quot;If I have a 3 terminal fixed voltage regulator, how do I make that adjustable? There is no Vref pin.&quot;<br><br>There are variable Voltage Regulation IC's that have what would seem to be a potentiometer inside them which is be adjusted within the stated range of the package. See the catalogs from Dalbani Electronics (Miami Florida), they'll mail you one. Or search their online catalog.<br><br>The fixed ones can be regulated in the fashion that Lee Wilkerson suggested.<br><br>Hook it up, pull out your DVM and adjust it to the voltage you need. <br>It's almost like a 'volume' knob for the voltage.
<p>Impressed! It&rsquo;s been a long time that I got interest to read what others write to have useful information that I further discuss among my gathering and it makes our time good. We make cross questions and answer them but for all that I read articles and this site has been on top of my list for providing such information. &lt;a href=&quot;http://www.fjackets.com/categories/Shop-By-Character/&quot;&gt;comic character jackets&lt;/a&gt;</p>
<p>A usufull addition to this article is how to determine the voltage of a radom LED in the junk bin</p>
<p>If you can access a variable voltage supply and an ammeter (if not supplied with the VVS) and a small supply of different resistors, the LEDs will be readily testable. Connect the ammeter in series with the supply resistor and the load (+ goes toward source +) then bring the voltage up slowly. Use a voltmeter paralleled with the LED in question to monitor Vf (Forward voltage drop) and watch the ammeter carefully. If the current starts to climb rapidly after the LED is lit, turn the voltage back down to limit it.</p>

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