LED resistor

[chieljan]

Hey people, this little thing was puzzling me (being quit a newbie at electronics:) ) : In the generalguitagadgets TS808 project the resistor used in series with the LED is 4,7M, and in the Ruby Amp project it's 1K. Why this difference? Both get 9V...
Made me wonder what resistors I should use, since I want to do both projects. I'm going to use the 5mm standard LED from banzaieffects (bright at 20mA, 50mcd, diffuse, 60 degrees). Fiddling around with various LED-Resistor calculators made me wonder even more...

Maybe someone here can help me? Thank you very much in advance;)

[brett]

Hi.
Most people use a resistor between 1k and 4.7k.  The higher end is for superbright LEDs (>1000mcds).
cheers

[Seljer]

err, 4.7M?  I think 4.7k would be more likely.

Those ultrabright LEDs can get really really bright so you might as well use a large resistor (even around) and save on the current for more battery life (in a simple circuit that doesn't use a lot like a fuzz face adding a LED can easily halve the battery life).
It doesn't really matter that much, as LEDs are usually more a thing of convenience. Smaller resistor = more current gets through = brighter LED.

[mikey]

The GGG TS-808 has a 4.7K there not 4.7M in case that wasnt a typo in your post.  That would cause some confusion.

[RedHouse]

Best way is to use Ohm's Law.  V/I=R

Say you have an LED that runs 20mA at full brightness, and a power supply of 9v...

9v / .020 = 450 Ohm Resistor

Say you want to add an 16mA LED to your car to indicate when your fog lights are on...

12v / .016 = 750 Ohm Resistor (or nearest value)

[petemoore]

  I used a 10k as variable resistor [wiper and outside lug], set to 10k Then adding supply voltage, adjust to desired brightness, remove pot, measure found resistance, replace with fixed resistor.
  Adjust the pot slowly and don't go near 0k or you'll burn the LED up

[Satch12879]

  I used a 10k as variable resistor [wiper and outside lug], set to 10k Then adding supply voltage, adjust to desired brightness, remove pot, measure found resistance, replace with fixed resistor.
  Adjust the pot slowly and don't go near 0k or you'll burn the LED up

+1; burning an LED is not pretty nor does it smell very nice.

I tend to skirt the line with high brightness in my builds myself.  The point is of those indicators is to be intentionally bright, so I'll sacrifice current draw for intensity particularly since I build to be run from a DC power supply.

[petemoore]

  I said something about burning up LED.
  To see what the thing actually looks like and to get an idea of how bright they can get and blow one up, there are a number of different ways. This is a current limiting resistor...I should have elaborated...the LED will raise in brightness to a point, soon after the point it levels out at max brightness at some given R value, it will burn out.
  [running @ Max brightness may lessen the life of an LED?]
  Since 1k was the mentioned minimum, tack a ~1k stop resistor to the pot for LED safety.
  "this is what I did" ...use at your own risk. May be a bad idea.
  i can see how it'd be a drag to join the 'I burned an LED club'. ..when that was your last LED...lol

[blanik]

i was looking for a type of LED for my projects, the reason i'm building DIY effects is the low current draw of most DIY Fx compared to Boss type pedals (specially the Delays) to get rid of the power supply of the pedal board (for years my pedal bord had a PS for hungry digital Fx like delay and Whammy pedal, my other effects (dist, wah...) had a PS jack and wire that lead to a couple of 9V battery holders screwed on the back wall of my pedal board and all wired to a small switch (4PDT) so when i closed my pedalboard i just had to close the switch and i could leave the pedals connected, since those effects had low current draw, i just had to change batt once every 6 months... there was also a LED on the switch box to easily know if the power was on or off) so my main reason to built the Rebote 2.5 was it's low current draw but i realize now that i'm really dependent on LEDs (specially live) so i want a type of LED thats doesn't require much power...
(on the same subject, i got a Behringer pedal recently and i was impressed with that tiny led, it lights up my room!  what kind of LED is it??)

R.

[petemoore]

  I believe "Super Bright LED's" will provide the most lumens for a given amount of current.
  I have an EQ700, the little 'sizzler' [red LED] can't possibly be missed.

[Stephen]

The price of a soper bright is close to a dollar and change ...what I can find!!!

Now there may be different ones but I mean superbright!!

http://www.monteallums.com/Product_links.html

Go here he sells the really good ones ...look like the ones in mouser.