Mastermech said:
I want to use a few diode to light a shadowbox and am curious about wiring
it up.
I understand basic electronics etc but am curious about battery life plan
on using 9v, and if a resistor is actually needed, or can I run a few in
series and be done with it.
thanks in advance.
The resistor is needed if you want to have any say whatsoever in how
bright your LEDs are, not to mention to prevent you from accidentally
letting the magic smoke out. Check the data sheets for your LEDs,
they'll have a forward voltage drop listed. Figure out how many lights
you need, in series you have a total forward voltage drop of N * Vd.
At this point, if you don't care too much about repeatable amounts of
illumination, you can just take however much voltage you have left in
your 9V, divide by the amount of lighting current you want, and place a
resistor of that size in the series to set the current. This will work
quasi-well. The problem is that a 9V battery is really a 9V _nominal_
battery, and will usually start around 9.5V or so and make it down below
7 by the end of it's life. If you want more regulation over the
intensity than those numbers provide, and/or to run the battery farther
down before it dies, you're going to need to be more creative. Linear
regulated current sources are fairly simple to do (though substantially
more complicated than a string of LEDs, a resistor, and a battery) and
will give you better brightess constancy. To really use as much of the
battery as there is you'll need to go to a switching regulator, which is
even more complicated and which, judging from your initial post, you
will most likely not be able to get to work.
So to answer your question in short, maybe.
