Switching LEDs from PC - newbie help required

[Steve]

For my MAME cabinet I want to be able to switch 4 LEDs on or off via the PC
(parallel port, I'm thinking.)
Now, I realise that my superbright white LEDs (130mW, 3.5V) cannot be run
from the parallel port directly, as the port won't supply enough power, so
I'll need to use the port to control relays or something that will switch
the required LEDs on or off (that are powered directly from the PC PSU.)
Now, I can use a soldering iron but I'm pretty much an electronics newbie.
Does anyone know where I might find a circuit to build that will do all
this, or else a premade kit I can purchase (Jaycar?)
My ability is around the level of soldering wires and using a multimeter, so
the simpler the design the better. I'd like to ensure I can't blow up my
parallel port, so feel free to point me to an opto-isolated design or
something.
My searching on the web also turned up this:
http://www.oceancontrols.com.au/controllers/parallel_relay_k074.htm
A parallel port relay board, which costs $54, and sounds like it may fit the
bill. Is this the kind of thing I'm looking for, or is it pricey and total
overkill? I doubt I'd need the circuit to be bi-directional for my own
requirements.
Thanks for any info.

-steve-
Brisbane.

 

[dmm]

For my MAME cabinet I want to be able to switch 4 LEDs on or off via the PC
(parallel port, I'm thinking.)
Now, I realise that my superbright white LEDs (130mW, 3.5V) cannot be run
from the parallel port directly, as the port won't supply enough power, so
I'll need to use the port to control relays or something that will switch
the required LEDs on or off (that are powered directly from the PC PSU.)
Now, I can use a soldering iron but I'm pretty much an electronics newbie.
Does anyone know where I might find a circuit to build that will do all
this, or else a premade kit I can purchase (Jaycar?)
My ability is around the level of soldering wires and using a multimeter, so
the simpler the design the better. I'd like to ensure I can't blow up my
parallel port, so feel free to point me to an opto-isolated design or
something.
My searching on the web also turned up this:
http://www.oceancontrols.com.au/controllers/parallel_relay_k074.htm
A parallel port relay board, which costs $54, and sounds like it may fit the
bill. Is this the kind of thing I'm looking for, or is it pricey and total
overkill? I doubt I'd need the circuit to be bi-directional for my own
requirements.
Thanks for any info.

-steve-
Brisbane.

You could use that, but it would be expensive and you would still need
resistors to limit the current throught the leds.

You can drive these leds fairly simply using transistors and a couple of
resistors. An even simpler way is to use a ULN2003N, which has 14 transistors,
(arranged in a Darlington array) resistors, etc in the same package.
You can purchase them from Jaycar - .ZK-8855 for $3.50 ea.

A resistor will still have to be used to limit the current throught the led.
We'd have to get the datasheet of the led (require the manufacturer and
part number), and the DC power supply voltage to determine the value
of the limiting resistor.

This link shows how you can use the parallel port to drive various loads.
http://www.hut.fi/Misc/Electronics/circuits/parallel_output.html

The last circuit in the link is essentially what is inside the ULN2003, except
for the opto-isolation, and there are 7 of them inside the chip.

 

[Steve]

You can drive these leds fairly simply using transistors and a couple of
resistors. An even simpler way is to use a ULN2003N, which has 14 transistors,
(arranged in a Darlington array) resistors, etc in the same package.
You can purchase them from Jaycar - .ZK-8855 for $3.50 ea.

A resistor will still have to be used to limit the current throught the led.
We'd have to get the datasheet of the led (require the manufacturer and
part number), and the DC power supply voltage to determine the value
of the limiting resistor.

This link shows how you can use the parallel port to drive various loads.
http://www.hut.fi/Misc/Electronics/circuits/parallel_output.html

The last circuit in the link is essentially what is inside the ULN2003, except
for the opto-isolation, and there are 7 of them inside the chip.

Thanks for the info. The white LEDs I'm using are from Jaycar, part number
ZD1990, which no longer seems to appear in the catalogue. 3800 mcd. Probably
very similar to their part number ZD0142, but I'm going to email them to see
why it's no longer carried by them. I bought them back in March 2003, but
didn't think to get specs on them as I thought they'd be sold for a while
yet.