Simple music light show (lpt led)

Step 2 Scheme & testing

Electrical scheme is really trivial, just connect leds to the LPT (parallel port) of your computer. Lpt outputs about 5V so if you are using white or blue high power leds you don't need resistors for them, just add 10-100 ohm for safety. ( if you are using red, green or other colors, use proper resistors acording to desired voltage, usually 200-300 ohm ). Longer feet of the led is anode (+).

I had to test if the plexi is translucent enough and if it is even working, right?

check video from testing on my desk..

In real world is even better looking because eyes are slower than digital camera, so it is glowing nicely.

Comments

[karthikcool90]

wt will happen when we use extra LED's instead of resistors ???
like making a series of 3 LED's and connecting it to the pin ???

[yznaction]

Would it be possible to use a usb Parallel port adapter with this setup?

[fwjs28]

a usb port would require an extra piece, like a micro-controller...a Parallel port would be possible though with a similar set up (i am no expert in electricity nor I/0 ports so don't take my word as religion )

[yznaction]

alright, i just ask because i only have usb ports on my laptop and I know there are a few companies that sell usb to 25 pin dsub parallels adapters

[fwjs28]

ahh, i would try the convertor...see what you can do

[cheeyah]

It is a good idea to put in a resistor even if the supply voltage matches the rated voltage of the LED. It is there simply to limit current, so something like a 1 Ohm resistor will protect your LED's.

[scgtrp]

The resistor is there to protect the parallel port, not the LEDs. A new motherboard is a bit more expensive than a few LEDs, and you can easily kill your parallel port (and the motherboard, if it's onboard) by drawing too much current.

[joudas]

yea, you are right, fixed

[Matir]

You'd want something bigger than a 1 ohm resistor for protection. Based on V=IR (Ohm's Law), for a 5V supply (LPT), a 1 ohm resistor gives you 5A of current. Something on the order of 500 Ohm (470 is commonly cited in online guides) gives 10mA, which is much more on the scope of what a parallel port handles well. Unfortunately, the spec for parallel port limits sourcing to 2.5mA per pin, so theoretically you'd need something like 2k Ohm, leaving you with an awfully dim LED.

[Padlock]

Where did you get your specs from? When I tested mine a little while ago I got about 20 ma per pin...

[thetech101]

According tom my online calculator, an 82 ohm resistor should work. That assumes the LEDs forward voltage is 3.5.

To the author, view this site: http://led.linear1.org/led.wiz

[joudas]

yea I know all the led stuff, and actually I'm using no resistror at all. But you have to be careful and know what you are doing. For this instructable let's make it 82ohms :-)

[thetech101]

The resistor value depends on the forward voltage of the LEDs. As the forward voltage changes, the resistor value moves up and down accordingly. And different color LEDs require different operating voltages.

[huang.wencong]

I think you should put a resistor in the anode of every LED's. The DB25 port (aka LPT / Printer Port) generates around 3.3VDC-5.0VDC. Let's just say it gives out 5.0VDC. LED's need 3VDC with 20mA current (around this). So by using Ohm's Law (R=V/I) you can count that R=3000/20=150 ohm. Maybe putting 150ohm resistors in every anode of LED works better.

[yamahamaxim]

Call me naive but what does the software look like for this? I'm not much of a programmer but I'd love to build an LED lightbar to mount on my PC showing CPU usage. thx

[joudas]

screenshots added