Total noob question: what resistor do I need to connect standard 3mm red led to 12v PSU power cable (same as for hdds..)???
http://linear1.org/ckts/led.php I don't know what you mean about the hdd's? Do you mean your 3mm led is the same as the hdd activity indicator led There really needs to be an led sticky made, there's at least one thread a week made asking how to use leds. Since you are a mod cpemma, i nominate you to do it
no, I mean PSU 12v power cable, same as used to power hdds... not hdd led... I want to connect a row of leds to 12v power cable - I need one resistor at the begginning of the serial row, right? What kind of res?
ok, so fro example I have this led : http://www.rapidonline.com/Electronic-Components/Optoelectronics/3mm-LEDs/Miniature-3mm-LED/29349 3mm red led, 25mA, it has Vr 5V, does it mean max volt can be 5, so I cannot use it with 12v?
You can use it with 12V. The typical forward voltage (Vf) from the datasheet is approximately 2 volts for the red LEDs. What this basically means is that when they're on with a reasonable current (i.e. 15-20mA) there should be about 2V across each. From this, you can calculate the resistor needed using Ohm's law. The calculator I linked to will do this for you. The parameters you want are: Source voltage: 12V Forward voltage: 2V Forward current: 15mA # of LEDs: however many you want, up to a max of 5.
The Vr refers to the reverse bias voltage. The forward voltage is about 2v so heres what we do: Source voltage is 12v each LED takes 2v and the current is about 25mA, assume we have 5 LEDs IN SERIES. Thats 12v-(5*2v)=2v, V=IR, V/I=R, 2v/25mA = 80 ohms. Buy the 80 ohms and 120 ohms, the 120 is just for protection try it first if the LEDs are bright enough stick with it. If not, swap it out for the 80.
There already is a very good guide by SteveyG in the Useful Links (Electronics) but n00bs are unable to find anything themselves. I blame their mothers for pandering to them.
sorry - last question - waht kind of resistors I should buy - metal or carbon film? http://www.rapidonline.com/Electronic-Components/Resistors-Potentiometer Also what W should they be? 0.5W?
OK... Just to be sure, I need to ask sth else before I go to Maplins to buy stuff So - I'm going to use series of leds - max I can use is 6, right? 12v from PSU cable minus every 2V from led - I have to use 1R (1ohm) resistor for this kind of serial led chains.. right? For 5 leds it will be 100R (100 ohms), for 4 - 220ohms, for 2 leds - 470ohms and for one led - 560ohms resistor. is that right? Now the problem is what if I need to use more then that? for exmple I will need a nice "chain" of 10 leds. So I will solder 2 series of leds - 5 leds in each, right? Question is - what then?? Can I just solder them togehter in parrarel or do I need to use another 12v PSU cable for second 5led chain? (Sorry, it is stupid question, but I'm not good at all in electronics... I can almost feel like the answer would be sodler together, but I need to ask, before I burn my PSU Oh, one more thing - I would like to use mini jack plugs to plug all those led chains to one junction box - I will solder all those chain inside the box but all will have separated cable outside. Question is - do I need stereo plug? or just those - 2.5mm screened plugs (one with code 20-0050)? http://www.rapidonline.com/Cables-C...ideo/Jack/Screened-miniature-jack-plugs/63479
