Re: how to connect an LED to PC

mrdarrett@xxxxxxxxx wrote:
ehsjr wrote:

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.


Ah. I was planning on driving even bigger loads than my incandescent
lamp. I drove a 1A 12V blowdryer fan with an IRF530, with the setup on
my website. My MOSFET got kinda warm - about 105 F with a heatsink.
(I used a diode and two caps as the 555 PWM circuit recommended.)

Is a 3.3k still good for an IRF530?

Thanks!

Michael


Hmmm... since you change the design with every post, I'd
recommend a "universal interface" between the parallel port
and the device driver you choose. The interface would be
there strictly to protect the parallel port, and/or to
drive low current (< 175 mA) devices directly.
You would use the output from it to control the driver
for whatever device you intend to use. A ULN2003 comes in
in a 16 pin DIP and provides 7 darlington transistors
so you can use it for 7 pins. You could use a 3.3K
resistor between each PP pin and the corresponding
input pin on the ULN2003.

With regard to your IRF530 - putting 5 volts on the
gate won't turn it all the way on. The resistor at
3.3K would be fine*, but the gate voltage is low.

* = you need very little current on the gate - except
when you need rapid turn on. But your 5 volts already
is a problem which superceeds that.

Ed
.

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