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General Category => General Discussion => Topic started by: bravodog on May 16, 2009, 07:00:04 AM

Title: Help please
Post by: bravodog on May 16, 2009, 07:00:04 AM
Ok so where is a good place to buy 180 ohm resistors for led's? on line or off line here in the states that wont cost an arm & a leg and is this a good general resistor to use for led lighting projects?  I was told by someone that I could do a 3x12 set up what ever that is??? <----- some help here or a picture would be nice too  ;) with 180 ohm resistors, Now is this 1 resistor to every 3 led's ?  I plan on using about 100 or less of them for back lighting on a custom air brushed 6x12 car tag and I want the light even across the back.  The led's are 5mm flat top 180 deg. view if that helps
Title: Re: Help please
Post by: spic0m on May 16, 2009, 09:28:46 AM
For calculating the resistors you should use Dr. Calculus (http://pcbheaven.com/drcalculus/index.php?calc=leds). You can try all the combinations you want.
For shoping i prefer Futurlec (http://www.futurlec.com/index.shtml), much cheaper than in my country and with enough variety.
Title: Re: Help please
Post by: kam on May 16, 2009, 09:34:31 AM
A good place for resistors... i generally get most of my staff from futurlec.com. They have some good prices there. Also, you may find some very good mushrooms on ebay. But take extra care when selecting seller.

180 ohms resistor is not to be considered as good or bad. An 180ohm resistor would be good if for example lighting an LED at 9volts. In general, you need more than one type of resistors to be safe.
I have a set of resistors about 30 of them.

For your project now, you need to tell us specifications of the 5 mm LEDs to calculate them. In general, 5mm LEDS would draw about 40mA current and would operate at 3.1 volts but this is something to confirm. Now, according to this LED theory here (http://pcbheaven.com/wikipages/LEDs/) that i strongly recommend you to read, i would choose to have sets of 3 leds in a row. Considering that the car voltage is 12 volts, the resistor needed would be 67.5 ohms. Now, this is not actually a resistor value that exists, so i use this standard value resistor calculator (http://pcbheaven.com/drcalculus/index.php?calc=standarresval), i go for 5% resistors (E24), paste this 67.5 and the best match would be 68 Ohms. That is what you need. Series of 3 LEDs connected in series with a resistor 68Ohms. But again, you need to make sure that the voltage and current of the LEDs and the voltage of the car are correct.

A simple schematic drawing for your application would be as the attachment.

As for the number of LEDs, each series would draw 40x3 = 120mA. So, keep in mind that you need to have about 33 lines of 3 leds, and that would result 33x120 = 3960 mA. This is about 4 amperes. Have the right cable used and not the good old handy color ribbon cable as it could be toasted.

Title: Re: Help please
Post by: bravodog on May 16, 2009, 19:21:19 PM
Ok here is the spec's on the led's them self's

Specifications:
Size (mm) : 5mm
Lens Color : Water Clear
Reverse Current (uA) : <=30
Life Rating : 100,000 Hours
Viewing Angle : 20 ~ 25 Degree
Absolute Maximum Ratings (Ta=25°C)
Max Power Dissipation : 80mw
Max Continuous Forward Current : 24mA
Max Peak Forward Current : 75mA
Reverse Voltage : 5~6V
Lead Soldering Temperature : 240°C (<5Sec)
Operating Temperature Range : -25°C ~ +85°C
Preservative Temperature Range : -30°C ~ +100°C

As far as a board goes I snagged a couple of these from e-bay I just didnt buy resistors when I got the led's and boards

(http://c-leds.com/pics/2_pcb_100_led_combo_pack.jpg)

The boards are nice and all the led's light up. <--- tested via breadboard )

Thanks Allot for the help guy & gals <---- dont know which you are?  I wasn't sure if this needed to be posted here or somewhere else.  I just hope this electronics NOOB doesn't drive you nuts with all the questions I am going to have.  Perhaps you should make a Noob corner on the site LoL
Title: Re: Help please
Post by: kam on May 16, 2009, 20:52:07 PM
you missing the forward operating voltage that is most important to our calculation...
Title: Re: Help please
Post by: bravodog on May 16, 2009, 21:08:15 PM
you missing the forward operating voltage that is most important to our calculation...

This would be the 12-13+ volts off a car batt ?  If your meaning the supply volts
Title: Re: Help please
Post by: kam on May 17, 2009, 01:59:38 AM
This would be the 12-13+ volts off a car batt ?  If your meaning the supply volts

No not really. Within the specs you gave the Max Continuous Forward Current : 24mA. What we also need is the voltage that each LED operates. That is also very important. Can you find it? Usually it is between 3-3.5 volts but this is not standard.
Title: Re: Help please
Post by: bravodog on May 17, 2009, 05:53:43 AM
Found it out its 3.0-3.2
Title: Re: Help please
Post by: kam on May 17, 2009, 20:03:43 PM
perfect.Then go as per my previous attached schematic. Make sets of 3 leds + resistor. You can calculate each line's resistor using this led resistor calculator (http://pcbheaven.com/drcalculus/index.php?calc=leds)

For your LEDs, if we suppose that the voltage is 13.2 (when battery is charging), then you need resistors of 150 Ohms.

Connect as many of those sets as you want in parallel. The total current will be the sum of currents of the number of those sets. Just to calculate your wire, nothing more.
Title: Re: Help please
Post by: bravodog on May 19, 2009, 05:33:03 AM
Thanks Kam  :)  Sorry I didn't reply sooner but my home system HD decided to take a dump on me and I have been re-building my system.  I am having to use the work lap top to get this out. this below is something I want to do also soon down the road as well as work with some pic's so be for warned I will be pestering you all soon with a ton of Noobie questions LoL

http://www.youtube.com/watch?v=iYNZ6hR_1JQ (http://www.youtube.com/watch?v=iYNZ6hR_1JQ)
Title: Re: Help please
Post by: kam on May 19, 2009, 08:09:58 AM
looking forward to your questions ;)

Good luck with your pc and constructions. And we would be happy if you make some pictures or video and upload your working project to our forum.
Title: Re: Help please
Post by: bravodog on May 21, 2009, 02:22:42 AM
Good luck with your pc and constructions. And we would be happy if you make some pictures or video and upload your working project to our forum.

Thanks Kam, Got the puter up & running, now I just gotta get all the proggies and stuff back on it and tweaked just right ;)  As far as pictures and videos goes that a roger on that.  I just gotta find some better soft ware for my kodak camera cause that easy share crap that came with it is what crashed the hard drive on my system.  any suggestions anyone?
Title: Re: Help please
Post by: kam on May 21, 2009, 08:06:52 AM
When you connect it, doesn't the computer recognize it as external drive? Cant ou just copy/paste photos? You need software?
Title: Re: Help please
Post by: bravodog on May 22, 2009, 05:59:58 AM
When you connect it, doesn't the computer recognize it as external drive? Cant ou just copy/paste photos? You need software?

Well the kodak easy share software had some really cool stuff you could do to photos as well as movies taken with the camera but thats ok I will find a substitute for it.  it's just a PIA to redo this system as it was also my game playing system.
Title: Re: Help please
Post by: bravodog on May 25, 2009, 22:43:24 PM
OK I'm going to get some resistors (carbon film) from futurlec do I need to get the 1/4w, 1/2w or the 1w ones for this little endeavor? 
Title: Re: Help please
Post by: kam on May 26, 2009, 15:36:54 PM
OK I'm going to get some resistors (carbon film) from futurlec do I need to get the 1/4w, 1/2w or the 1w ones for this little endeavor? 

For general purpose, 1/4 are just fine. Unless if you want to carry heavy loads like tens of parallel LEDs or something else. 1/8 are fine also but very small and harder to handle. 1/4 are ideal for general use.
Title: Re: Help please
Post by: bravodog on May 27, 2009, 03:04:01 AM
TY again Kam I got a couple hundred ordered today ;)  Just to have some spares to play with.
Title: Re: Help please
Post by: kam on May 27, 2009, 15:20:55 PM
TY again Kam I got a couple hundred ordered today ;)  Just to have some spares to play with.

futurlec has a great deal when you get such things. There are some very nice lots to get from there in very good prices, maybe the lowest i've ever found, with parts that are commonly used. Resistors, capacitors, transistors, linear ics etc. There is for example a $3 (or something like this) bag with 100 capacitors with different sizes... You should try them.
Title: Re: Help please
Post by: spic0m on May 28, 2009, 00:05:29 AM
My futurlec order arrived today, hehe.  ;D ;D ;D ;D
Title: Re: Help please
Post by: bravodog on May 28, 2009, 04:56:27 AM
My futurlec order arrived today, hehe.  ;D ;D ;D ;D

Sweet!!!!  But you got 2 leg's up on me cause you know what to do with all that stuff LoL

Aww man I just looked at there ship time for me and reg. is 1-2 weeks del. time???? they got some good prices but the ship is a tad dodgy.
Title: Re: Help please
Post by: kam on May 28, 2009, 15:14:27 PM
yes that's a problem... In Greece we get 6-7 working days.