Re: how to connect an LED to PC

mrdarrett@xxxxxxxxx wrote:
ehsjr wrote:

mrdarrett@xxxxxxxxx wrote:

ehsjr wrote:


wills.kingspanama@xxxxxxxxx wrote:


Greetings,
How to connect an LED to the PCs PPI and make it glow by program?
Thanks in advance.


http://www.epanorama.net/circuits/parallel_output.html#circuithow



So if it's 2.6 mA max (data pins to ground), are the 470-ohm resistors
still necessary? (grin)

Michael


Where's you get 470 ohms? That won't limit the current enough.

Ed



I posted a page on my website re: controlling a light bulb by parallel
port:
http://mrdarrett.googlepages.com/blinky

Is a 2 k-ohm resistor big enough? Should I make it larger, just to
stay on the safe side?

Coming soon: PWM motor control via parallel port.

Michael


You don't get a lot of base drive with that 2K resistor,
and yet you want to be darn sure you protect the port.

If you really intend to drive an incandescant bulb, you'd
be better off with a darlington, like a TIP120. In terms
of figuring the base resistor, you would be able to use a
4.7K. The TIP120 in your circuit with 4.7K base resistor
could drive a bulb that needs up to 1 amp.

You can use the idea embodied in the circuit with a small
transistor and drive a LED with that circuit, provided you
put a proper resistance in series with the LED.
Here's a diagram:


+9 --------------------+
|
[470]
|
[LED]
|
/c
Pin 2 -----[3.3K]---| PN2222 or similar
\e
|
Gnd -------------------+

The above will give you about 15 mA through
the LED, and limit the current drawn from
the parallel port to ~1.5 mA, worst case.

Ed
.

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