maxprivate the reason ur burning LED is cuz ur not using the correct resistors to drop the forward voltage and maximum current through each LED.. .. or u bought some cheap *** leds.... but i doubt that...

 

+1

 

I see a potentiometer and can anyone tell me their relationship to resistors?

 

all the pot does is regulate the duty cycle to the LEDS... IT HAS NOTING TO DO WITH ANY CURRENT REGULATION TO THE LEDS... they always run on the same voltage/current... all ur changing is the Duty Cycle....

 

i got the leds fron the ctwich guy on ebay,hes the guy who most orgers get there leds from. and i got free resistors with the leds and these are the ones im using. so im guessing they are the right size, im not sure. what size resistors should be used?

 

and thanks for clearing up the fact that you could get reverse voltage flow, i know that all the diode is..is an electrical gate valve that allows current flow one way.

 

No electrical devices are ideal; a diode can actually have reverse current flow given enough voltage, and doesn't actually have a constant voltage drop.

LEDs... well, the acronym is "light emitting diode," but I haven't worked with them enough to know of their properties.

 

a potentiometer is a variable resistor, it has nothing to do with duty cycle.

imagine a 10K resistor that can be lowered to any finite value from 0 to 10K, thats what a potentiometer really is.

U shuold not use a variable resistor with LED's. its a waste of money and there is no point to it. just buy the approriate resistors for the size of ur LED's

f550maranello2 : this is what duty cycle really is http://en.wikipedia.org/wiki/Duty_cycle

 

^^^^^ ok now u just dug urself into a hole and ur about to get owned.... ready

this is exactly what im talking about when people don't know $hit...

that pot adjusts gain to a 555 timer so the timer can adjust the duty cycle for the PWM circuit.... THAT POT IS NOT DIRECTLY CONNECTED TO THE LEDS....

Come one now did ya even read my post? I have a bachelors in electronic engineering... dont tell me i dont know what im talking about ok....

maybe u dont know why a PWM is used here do ya? the reason its used is because the use of resistors to dim the entire circuit would be bad cuz u would need a massive 100 watt resistor to make everything dim.. and that wouldnt even work good either because if u group the leds in 5 rows and u have 5 leds to every resistor u will not always get an even number of leds as a total for the board... so ull have 1 row of 3 somewhere and GOOD LUCK WITH MAKING IT DIM WITH THE OTHERS..., what will happen is that those 3 leds will be either brighter or dimmer than the rest of the board...


NOW... y use the PWM??? because of those 3 leds? How does that work u might ask?

Simple... ur ALWAYS keeping the same voltage and current to all leds.... ur just varying the pulse width with that POT... so it tricks ur eyes into thinking that they are dim when in fact they are using the same power but are flashed at a different rate....

 

great explanation! now as to the proper size resistor for these leds? i am using 3mm leds 4000mcd and the resistors came with the leds free. i never ohmed the resisters out to see what thier value is. let me know the correct value i should have is and i'll ohm out the ones i have and let you know. if i have to change out leds all the time that would suk.

 

The issue is that there isn't a specific value resistor that will work, which is why our friend Kevlo uses PWM.

The value of the ideal resistor depends on the voltage the LED wants, the current draw of the LED, and the voltage coming into it. Unfortunately, while the first two values are pretty constant and can be found on the LED's datasheet, the voltage of your cars electrical system changes, based on your battery, your alternator, and how much current your car is drawing. It changes very quickly, which is why you see a lot of cars with a voltmeter next to the temperature and oil gauges. A resistor that gives you the correct voltage drop at 12v is not going to give you the correct voltage drop at 14v, or vice versa.

However, the bright (haha) side is that you could put together a LM31x voltage regulation circuit for a few bucks in parts. Find out the voltage drop and the current across each resistor, find out how they're wired. The LM31x stuff can do like 1.5 amps, which is more than enough for LEDs. Once you find out what the total voltage drop of each assembly, all you need is a single IC and a few resistors and maybe a diode or two (The last digit of the IC is the voltage, so if you need 5v, you would use a LM315, etc.)

 

f550maranello2 : i was talking in general what a POT does, not specifically in this particular application, i just defined it...i guess this is a misunderstanding - i guess i should have made that clear in my post...and u should relax my friend, i never said u dont know what u r talking about!

oh and and i graduated Seneca college 2 years ago for Electronics Engineering Technology - Communications (3 year diploma program), maybe not as good as a bachelors but i have built an a few amplifiers in my day

 

no harm done... sorry to be all loud about it but... i dont think anybody besides like 3 people understand what goes on here... is cool

 

I know you knew this, but for clarification, it wouldn't be flashed at a different rate. It would be a different duty cycle/pulse width, but the same rate.

 

yea different rate of duty cyle...thats how i meant to say it so people understand... the frequency stays the same....

anywho... thats how it works and its the best way to do it...