|
If you have a few Red LEDs looking for a purpose, this desk lamp looks like a great project. Might be able to do it with a little less regulation but taking the cautious road never hurts. I have found the resulting light extremely useful when observing. No more holding the flashlight in your mouth when reading charts or making observing notes. Because the light can light up a whole area when turned fully on it can be used as a worklight when breaking down gear and packing it into the vehicle without bothering other observers at a dark observing site. Or build the 120V version for a personal observatory.”
|
July 28th, 2006
If you go to National Semi’s site and have a look at the spec sheet for the LM317 you
will see one neat trick: You can run the 317 as a constent current source. The neat
thing about this is you can make the regulator board so it will work with any color LED
without changing anything except the LED. You can go from red LED’s to white LED’s and
if you set the regulator to give the LED’s 25ma, that is what they will have going
through them.
With a voltage regulator setup like you have, you need to be concerned with running
the LED’s over their rated current. If for example you set up a chain of blue or white
LED’s and then set the pot for 25 ma through them then switch over to red LED’s, the red
LED’s will have more then the 25 ma through them unless you set the pot again for the
voltage drop of the red LED’s.
The constent current source is a nice idea for little LED fidgets because it lets you
not have to worry about the wall wart you use or the LED’s you use. You can use whatever
you have on hand and it will work properly.
July 28th, 2006
Thanks for the info Matthew.
December 9th, 2007
Nice to see my design and photos getting around, but a little more credit to the original author might be appropriate.
The original posting is at http://www.siowl.com/atm/redlamp.php
You could get more efficient or elegant with the circuit. The whole concept was setup to allow electronic neophytes to build it successfully, thus the choice of the overkill (and cheap) LM317 in voltage mode. Over 60 of these have been successfully made in garage workshops by members of a local astronomy club. A great little exercise allowing people to learn a little electronics and soldering.
December 10th, 2007
Hi Silicon Owl,
Great to hear from you! Your site is linked in the article.
The Make article where it was found is also linked to.