M
maneesh
Guest
[please post as this mailbox is full of spam)
Hi all,
I've got a simple problem I was wondering if I could get some help
with, if you don't mind responding please insert all the digression
you like (I will be a little verbose, please point out if I have
something wrong), as I would like o gain a better understanding of
what to do. My knowledge of electronics is quite shameful.
I need to be able to control an LED (perferably two) from my computer,
I would also like to control their intensities, but I've come to the
impression that it would be hard to do because LED brightness is
controlled by current and not voltage (why am I having trouble
understanding that?), so something like a DAC hooked to the parallel
port won't work (how much current does the parallel port supply
anyway?).
Special note: I have a special 300 nm emission LED, which is
expensive. The company says it is just like any other LED, but I have
to be careful of reverse bias. THe only way this can happen is if I
put it in backward, no? It's also got a ground pin, which I can guess
goes to ground, but I have difficulty understanding exactly why you
need it...
Also here are the specs:
Typical Maximum Condition
Forward voltage: 5.5 7.5 IF=20mA
Does this look like a normal LED to you in terms of voltage and
current reqs? Should I be able to drive it from the parallel port
(+5V vs. +5.5V?) of a PC? Will I need an external powersource (should
just a plain old electronics adapter do?)? Is there anything else I
need to worry about (potential powerspikes that could blow the LED
etc.)?
I was suggested some prestuffed control boards like from iowarrior
(it'd be convinient to be able to control these LEDs with USB from my
iBook)....but apparently they don't have enough power to drive my LED.
And it seems like overkill with a few of these other control boards
(I am not religous about software, but my life would be easier if they
had linux or OS X software/libs).
So I think that leaves me with a parallel port interface.
Does the following make any sense?
(please don't hit me with anything, I hope the ASCII turns out OK):
Resistor (? 5.5V/0.02A = 275ohms? Could I make this a
variable resisitor so I could alter the intensity with a knob?)
|
|
| -----pin D7 on parallel port (do I need
a
\/ |
resistor?)
|
|
|
+5.5V -------/\/\/\-----transistor(NPN)------|
|
----
\/ <--300 nm LED
----
|
0V ----------------------------------------|
Do I need to use the ground pin on the parallel port?
I suppose I could easily ad another transistor if my basic design is
correct for the second LED, if someone wouldn't mind posting the
actual resistor values (with a teeny explanation as to how you get
those values) I'd much appreciate it. I guess I could just do this on
a breadboard. Does anyone know of where I could by a convienient
dongle I could hook to my parallel port so I could just plug in wires
like a breadboard?
Many Thanks for reading if you got this far, I'd appreciate ANY
advice.
If I am on the right track, I'll mess around a little on my own and
reply in this thread with any specific questions (i.e. how do I know
which exact transistor to get?).
Hi all,
I've got a simple problem I was wondering if I could get some help
with, if you don't mind responding please insert all the digression
you like (I will be a little verbose, please point out if I have
something wrong), as I would like o gain a better understanding of
what to do. My knowledge of electronics is quite shameful.
I need to be able to control an LED (perferably two) from my computer,
I would also like to control their intensities, but I've come to the
impression that it would be hard to do because LED brightness is
controlled by current and not voltage (why am I having trouble
understanding that?), so something like a DAC hooked to the parallel
port won't work (how much current does the parallel port supply
anyway?).
Special note: I have a special 300 nm emission LED, which is
expensive. The company says it is just like any other LED, but I have
to be careful of reverse bias. THe only way this can happen is if I
put it in backward, no? It's also got a ground pin, which I can guess
goes to ground, but I have difficulty understanding exactly why you
need it...
Also here are the specs:
Typical Maximum Condition
Forward voltage: 5.5 7.5 IF=20mA
Does this look like a normal LED to you in terms of voltage and
current reqs? Should I be able to drive it from the parallel port
(+5V vs. +5.5V?) of a PC? Will I need an external powersource (should
just a plain old electronics adapter do?)? Is there anything else I
need to worry about (potential powerspikes that could blow the LED
etc.)?
I was suggested some prestuffed control boards like from iowarrior
(it'd be convinient to be able to control these LEDs with USB from my
iBook)....but apparently they don't have enough power to drive my LED.
And it seems like overkill with a few of these other control boards
(I am not religous about software, but my life would be easier if they
had linux or OS X software/libs).
So I think that leaves me with a parallel port interface.
Does the following make any sense?
(please don't hit me with anything, I hope the ASCII turns out OK):
Resistor (? 5.5V/0.02A = 275ohms? Could I make this a
variable resisitor so I could alter the intensity with a knob?)
|
|
| -----pin D7 on parallel port (do I need
a
\/ |
resistor?)
|
|
|
+5.5V -------/\/\/\-----transistor(NPN)------|
|
----
\/ <--300 nm LED
----
|
0V ----------------------------------------|
Do I need to use the ground pin on the parallel port?
I suppose I could easily ad another transistor if my basic design is
correct for the second LED, if someone wouldn't mind posting the
actual resistor values (with a teeny explanation as to how you get
those values) I'd much appreciate it. I guess I could just do this on
a breadboard. Does anyone know of where I could by a convienient
dongle I could hook to my parallel port so I could just plug in wires
like a breadboard?
Many Thanks for reading if you got this far, I'd appreciate ANY
advice.
If I am on the right track, I'll mess around a little on my own and
reply in this thread with any specific questions (i.e. how do I know
which exact transistor to get?).