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Author Topic: LED question  (Read 5246 times)

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jbrs128

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LED question
« on: March 21, 2008, 20:24:33 PM »
Hallo all!
I am new to your site and i am glad to meet you as you have done a really good job!

i have 8 leds connected to an output of a ttl. The problem that i meet is that when 1 led is on, it is very bright. Every time another led turns on, the brightness is falling untill all 8 leds are on and they are no more very bright.
I put smaller resistor but it is a problem when 1 led is on. it is too bright and might destroy.
How do you solve this problem?

kam

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Re: LED question
« Reply #1 on: March 21, 2008, 21:29:44 PM »
I think you have 1 resistor for all LEDs is that so?

Because if it is so, change it. You need 1 resistor for each one led!

Erkeli

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Re: LED question
« Reply #2 on: March 22, 2008, 12:04:22 PM »
I had this prob again. The solution is 99% a unique resistor for each led. You can also use resistor packs that are made for this reason. Very easy and fast!

jbrs128

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Re: LED question
« Reply #3 on: March 22, 2008, 13:49:10 PM »
Ops you mean that for 32 Leds i have to use 32 resistors? This will double the size of my pcb  :-[

I had this prob again. The solution is 99% a unique resistor for each led. You can also use resistor packs that are made for this reason. Very easy and fast!

And what is really this resistor pack?

kam

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Re: LED question
« Reply #4 on: March 22, 2008, 17:51:22 PM »
Ops you mean that for 32 Leds i have to use 32 resistors? This will double the size of my pcb  :-[

Exactly!

And what is really this resistor pack?

Is a very good solution for your problem. It has almost the size of 2 or 3 resistors 1/4w but it actually has 8 resistors of the same seristanse with one common pin for all. Is like you have 8 resistors and one side of all resistors connects to the same position.
This means that it has a total of 9 pins (8 for each resistor and 1 for common). So, you only have to connect each cathode (for example) of every led to one pin of this pack and then connect the common pin to the negative. That's it. Easy fast and saves ALOT of space.

The attached image shows one of this resistor net and the equivalent schematic. it is not with 8 resistors but you know... there many many types to choose. just get an idea.

jbrs128

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Re: LED question
« Reply #5 on: March 25, 2008, 08:59:16 AM »
YES YES YES YES

Thanx thanx than xtthnx thanx!
 ;D ;D ;D ;D ;D ;D ;D ;D ;D ;D ;D ;D

Alex

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Re: LED question
« Reply #6 on: April 06, 2008, 23:19:14 PM »
Real good solution eh? Check also for DIP packages with resistors!