LED LDR question- ANd Ratshack

[jimbob]

http://generalguitargadgets.com/index.php?option=content&task=view&id=123&Itemid=141
Im going to build this tonight but i was curious about the led/led i would buy from the local ratshack. They have lots a diff things that LOOK like what i might need. DOes ti matter what kind of ldr i buy? Do i use your basic red 5mm red led? When i get the right parts i place them facing each other and shrink wrap. Until then i need to make sure i got the correct part.  Anyone?

[jimbob]

?

[toneman]

JB, see comments above about SupaSustain vs Roland Sustain.
tone

[toneman]

do a search here for "LDR"....
tons of hits....lots!! of info and discussions.......
try it u'll like it....
stayLDRed
tone

[Hal]

the LDRs at rat shack are a variety pack, and are ALL OVER THE PLACE.  They're not too expensive, though...under $3 for a 5 pack.  So buy a couple, and experiment for what you need.  Do it on a breadboard, with a shoebox you can put over it...

[sir_modulus]

for testing LDR's I find little black and grey film canisters to be really good for keeping out light. Ya, the RS ones are usually all over the place, and if you can't seem to find one...Small bear will open soon!

Peace,

Nish

[ragtime8922]

Or you can but a vactrol from Mouser or Newark in One. Part numbers are VTL5C3 and VCL5C4 (perkinelmer.com) Also, check out the Silonex website.

If you do the Radio Shack route then buy multi pak. They are flat discs with 2 leads comming out the bottom. The top sorta reminds you of a solar panel but the lines are coiled semetrically. The first one I built (for the Uglyface) used one that had a base that was a little bigger than the LED's base. Just get an index card and make a small tube with black electrical tape and use another piece of tape to seal the ends for each meter test. When you get what you want ditch the index card and use shrink wrap.

[SirPoonga]

Interesting.  Excuse my ignorance, but how do you control and LED/LDR combination?

[jimbob]

Great. Thanks for all the ideas- MIght just wait for smallbear.

[NaBo]

This is right up my alley!  I've been experimenting with LEDs and LDRs for the past few days.  I don't see any values for the LDR anywhere on the site, so it looks like you might have to do the same

First, you may wanna go check out this:  http://www.home-wrecker.com/uglyface.html
There's a pretty good run-through of how to make the optoisolator and what values to use and expect when building your own VTL5C3 work-alike.

Generally, an LDR that measures in the low kilohms in full light, and in the megohms in darkness should probably work fine.  Cadmium Sulphide (CdS - ratshack ones are this kind) LDRs work best with a green LED, Cadmium Selenide (CdSe) work best with red.  Standard LEDs should work just fine (max brightness of 5000 mcd in this application is probably way way over kill), just make sure it fits in your shrink tube.  A lot of that stuff comes from here: http://www.geocities.com/thetonegod/rockncontrol/rock.html

You should experiment with different LDRs, shielding the unit from light as best you can, keeping in mind the max resistance will probably still be greater once properly shrouded and such.  Resistors in series and parallel with the LDR can also be toyed with if you want, changing range and taper.  Dunno if i missed anything you should know... im definitely not an expert on this stuff, but im learning ... and i'll be picking up a few VTL5C3's when small bear reopens too!

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SirPoonga's query:  LED/LDR combos can be controlled many ways i'm sure, but most simple is just to have a variable resistor controlling LED brightness- like another LDR.  Looks like transistor gain as shown in the supasustain?  Breaking away from the optoisolator unit, you can use some type of shutter system between the LED and LDR.  Very, VERY cool stuff to play with.

[jmusser]

I used that ugly face build review as my source for putting together the optoisolater in my Ugly Face. In the pack of photocells from Radio Shack there are some that are just slightly bigger than the LED that they'll be paired with. That one had a 10 meg resistance, when I wrapped in in electrical tape and measured it. There are smaller and larger ones in that pack, buit the middle size seems to be the one. I wrapped the two together with masking tape so it would reflect inside the heat shrink, and then I but the heat shrink on. I left about a half inch tail sticking out over the leads, smeared super glue on the inside of the heat shrink, and then clamped it for a few minutes with some small vicegrips. It seems to work out pretty good that way. Be sure to mark the cathode of the LED before you enclose it. I believe it's the short leg, if you forget.

[jimbob]

I really appreciate everyones help and their time responding. I plan to experiment with all suggestions this weekend and ill post the results .

Thanks ALL!