Glow around 5 to 8 LEDs from a single arduino digital pin

Hey, I would like to know how i could glow around 5 to 8 LEDs ( RED ) from a single arduino digital pin . I know the code to make the pin high and stuff. What i want to know is what amount of resistance i need? since the digital pin of arduino gives only 5v will it be enough to glow 5 to 8 LEDs with that. A basic design would be helpful.Thanks..

You'll need more components to make that happen. 5 to 8 LEDs will draw too much current for a single pin to handle. You'll need to use a transistor acting as a switch to supply the current requirements of the LEDs.

You can connect them to the 5v pin on the arduino and run them to a digital pin - this should source enough current. However, you'll need an appropriate resistor.

Use a transistor like 2n3904 or 2n2222 as a switch, collector to 5v, emitter to positive side of LEDs in parallel, and a single resistor with a high wattage rating, or several with low wattage rating from the negative side of LEDs to ground. Digital pin thru a 1kohm resistor to the base.

thanks a lot for all the replies…even i too think that the digital pin wont be able to handle too many LEDs… and is it possible to use a BEL 100N transistor instead of a 2n2222 …and do all the LEDs have to be in parallel?and how many ohms approximately is required as resistance?

http://www.datasheetarchive.com/BEL100N-datasheet.html

if you connect the transistors base to the chip via a say 4k7 resistor, emmiter to ground, then you can connect the leds in series ( with one resistor ) to a higher ( 12v ) voltage as the transistor is a buffer. ( leds to +v and collector )

BEL100 should be fine. With regards to how much current it can handle, it is similar to the 2N2222 mentioned.

If the LEDs are in series then you need one resistor in line with them to limit the current. If they are in parallel each LED needs it's own current limiting resistor. For a 5v a Supply you need a300 to 500 ohm resistor. Google for an LED resistor calculator.

So is it easier to run 2 LEDs on one pin. I need to do this to my build just run to LEDs on one pin.

You can run 2 LEDs in parallel off of one pin, each with its own resistor, but the total current should be less than what the pin can supply.

The latest LEDs are pretty bright even at 5mA or so. So 2 of these drawing 10mA is no problem.