OK got some more of my project done but still need your help: I need to assemble a molex to power my led's, i have 3 led's which means 3 anode and 3 cathodes i was planning to have the three cathodes going through one ground but i wanted some more suggestions. What I want to do it power it through a molex so I need to assemble a connector can someone helpe me out... also i need to figure out what kind of resistor to buy, there are so many kinds and wattage %. Carbon film, metal film, and metal oxide film then there's 5% and 1% then 1/2 watt, 1/4 watt and 1/8 watt, that is where I am lost. http://www.linear1.org/ckts/led.php <---linear calculator So with the info given i did the math using linear's calculator and I came up with 150 ohms...well it might be wrong cause i did 20mA for three leds should I have done 60mA for three leds? I plugged in 12V as supply voltage and after adding up the voltage for the led's i came up with 9V. Can someone look it over and see if everything is correct. This is the specs for the three diff led's: 2.5 - 3 VDC @ 20mA 3.2 - 4 VDC @ 20mA 2 VDC @ 20 mA also i am really iffy on how to make the molex connector like what wire to what and crap like that and where would i pick up a molex connector (and wires) to work with. Thanks ~Beginner modder
molexes wre easy just np down to the local computer shop and buy a simple Y splitter cable. I am not sure of which wire is which off the top of my head I believe that yellow is 12V, but nip over to VH and check out their guides section, when I need the pinout, i go to the fanbus gudes they have, the 7V/0V/12V guide I do believe. Your math looks right to me although I have as much expierence with electronics and bulding ciructs as a neutered chimp. As long as you put the stuff into linear's calculator it comes out right, as im sure you did the first time. Looking at your setup you will probably need three different values of resistors since they are all different V's, and I personally would use the 5V line for that, less heat to dissipate. I dont think the resistor type makes a difference, except that some kinds are smaller and mre expensive than others. Have a go, its not too expensive and if you sit around worring about if you have gotten it right you will never get it done. I soldered for the first time in my life when I went to do my first led mod, it really isnt that hard, just make sure you have a a decent iron and some light solder or some flux core solder as it makes it easier to work. If you are doing more than one led consider a breadboard or prototyping board, as you can see MAcro used on MB it deffinetly makes it easier than trying to hold both wires, the soldering iron and the solder. I drilled into a piece of wood and electrical taped and hot glued it into place for my board, looking back I realsie i should have bout some board from radio **it
Firstly, yellow = 12v, red = 5v and black = ground Okay, resistors depend slightly. If the LEDs are to be in series or parallel then the values are different. parallel Code: () () () || || || +---+---+--- 12v | | | +---+---+-- ground series Code: 12v ---()--()--()--- ground Okay, so if they're in parallel it's easiest because you simply have a resistor for each LED worked out seperately. I forgot how to work it out in series, but I THINK you do add the amperage together. Please verify this someone. For the resistor wattage just take the LED voltage (let's say 3.2v) and the LED amperage (forward current) (let's say 31mA) and multiply them together. 3.2v * 31mA = 3.2v * 0.031A = 0.0992W As you can see, this is pretty much 0.1W, so a 0.1W resistor MINIMUM would be needed. It's MUCH better to go over, but a 0.125 (1/8) would be fine.
Hi, Ouikikazz, welcome to the BiT-Tech boards. I just saw your post on [H] as well. First, use my new and improved calculator: http://www.bit-tech.net/article/68/ Second, for parallel combinations, add the currents if you plan on using one resistor for all the LEDs. Pay close attention to the power dissipated in the resistor, and make sure you use a resistor with a high enough power rating. Third, for series combinations, add the voltage drops. Fourth, you usually use parallel when all your LEDs are identical. Even then slight variations can make one of them glow a little dimmer. Since you have three LEDs with different forward voltages, you should pick series, or run each one with its own resistor. The series case is: Vf (combined) = 2 + 3 + 4 = 9V Vs = 12V (since if you used a 5V supply, you wouldn't get them to light) Id = 20 mA (if these differ too, pick the lowest, but yours were the same) so R = 150 ohms, and the power dissipated is a low 60 mW so a 1/4W resistor will be just fine. Looks like you did just fine. The most common and inexpensive resistors (in the US anyhow) are 1/4W, 5% carbon film. Increasing the precision or the power dissipation isn't necessary in this application, so get the cheap ones. The resistor can go before or after the LEDs, or even in between them. Like the guys said, yellow gives you 12V with respect to ground. More questions? Ask away.
what I did was I ordered (resistors) 1/4W for the 4v and 3v leds and 1/8W for the 2V one because they didn't have the 1/4W 150ohms in stock. With help from TheCheeseMan also he said it's best to use three seperate resistors so I found three different resistances of 50, 100 and 150 ohms. Now soldering is the part I have alot of input on fron various sources. Someone has told me to solder the cathodes (negative) together by bending them towards each other than just soldering the ground to the end of the chain and for the anode (positive) where the resistors will be to just solder the resistors and then bend them towards each other like the cathodes and solder them together then solder the wire to the end of the chain. Just wanted someone to confirm that this would work properly. If not then how should it be done. Thx for the help
That sounds about right. Code: +--/\/\/\--|>|--+ | | +5V o---+--/\/\/\--|>|--+--o gnd | | +--/\/\/\--|>|--+
OK, let's review some basics. Elements in parallel all have the same voltage drop across them. So if you want to use this scheme, you would go and calculate a resistor for each LED, and I would suggest 5V source, since no individual LED needs > 5V to light it up. So each resistor/LED combination would have 5V across it, so you need to do the calculator three times.
so basically a 5v source would suffice? I have already done the math and got all the resistance just drawing and setting it up is the thing i'm really trying to figure out. Hey linear you got ICQ or AIM to talk to you directly? If so send me a PM.
You're good to go, just use 5V instead of 12V as you indicate in your drawing, and use 5 for Vs in the calculator when you figure the values for the resistors.
one last question linear....the 5v wire....should i strip it down to bare wire then solder and put some heatshrink on it or should i just make slits to solder...or would it be better to use a metal conductor and solder the 5v wire to the metal piece.? Thanks for the help
