Tremulus Lune CdS Photocell help, urgent!

[BAM]

Alright, heres the scenario:

I decided to build a tremulus lune, and coincidentally, i realized that i can use the building process as a project for a physics class. Its a win win.

However, i couldnt find one part: the CdS 5k light 500k dark photocell that goes with it. Mouser discontinued it, and since my knowledge on electronics is somewhat limited, i overlooked the substitutes i could have used at smallbear, thinking it needed to be an exact value. my mistake.

So now, I need to present this on Wed. of next week, and i have no CdS, and theres very little time to order such a part and have it here on time. (im gonna need some time to build it, plus everything else wont get here until Friday or Saturday.)

So i went to Radioshack and just grabbed what they have, a pack of 5 assorted photocells.

Below is a link which lists the values of each. Could anyone tell me if any of the values listed could be used and still have it work properly.

And is there any other store that might have them? I'm extremely desperate. Thanks in advance

-BAM

[Fret Wire]

There is no link on your post, and I couldn't find the specs on them. You can use the VTL5C2 Vactol.
http://www.tonepad.com/getFile.asp?id=84

BG micro has them cheap.
http://www.bgmicro.com/prodinfo.asp?sid=0459386574074074691664869&prodid=ICSVTL5C2&page=1&cri=ICSVTL5C2&stype=3&time_out=44:49

[idiot savant]

i was reading through the commonsound forums, because i'll be starting a panneur soon, and dann recommended a replacement

http://www.goldmine-elec-products.com/prodinfo.asp?number=G15177&variation=&aitem=1&mitem=1

he said so long as it is over 500k dark, and under 1k light it'll work.....

[Transmogrifox]

Yes--The Radioshack CdS cells will work very well.  I use them a lot.  The key is to make an enclosure with the LED that is very dark.  I have had some of my LDRs from Ratshack range as much as 10k to 4 Meg-ohms.  The only loss you may suffer from having a higher resistance when illuminated is some overall volume loss on the signal.  

With the tremulus lune's trimpot in the op amp output stage, you can adjust this for values up to 50k min resistance pretty dang easily.  

If you find an LDR with a factor of 100 between minimum and maximum resistance, this will give you a 40 dB change--which is a good deep tremolo.  Any one of those Radioshack CdS cells will make the tremolo effect work.  I think the one I found with the most resistance change was the little one with squared off sides (as if I couldn't be any more vague).

Anyway--here's the important thing:  do a good job of making the LED/LDR package exceptionally light-tight.  I have had good results using Epoxy and black fingernail polish.  Another thing that works is this:
thin layer of Epoxy--->black permanent marker--->thin layer of Epoxy--->black permanent marker...

When you're done, hold your meter on the leads, turn on a bright lamp, and hold it under the lamp.  Note your resistance reading.  Turn the lamp off, wait ten seconds...measure resistance.  If it doesn't change much (less than 5%), then you've made a solid capsule.  If it changes quite a bit from being held under the lamp to ambient light conditions, then you need more layers of whatever you're using to make it light-tight.

I'll bet JB weld will work real well for this, though I have not tried it yet.

[BAM]

wow, i feel like a fool not posting the link. anyway, here ya go. sorry about that :oops:

http://support.radioshack.com/support_supplies/doc38/38703.htm

[BAM]

There is no link on your post, and I couldn't find the specs on them. You can use the VTL5C2 Vactol.
http://www.tonepad.com/getFile.asp?id=84

BG micro has them cheap.
http://www.bgmicro.com/prodinfo.asp?sid=0459386574074074691664869&prodid=ICSVTL5C2&page=1&cri=ICSVTL5C2&stype=3&time_out=44:49

wow this looks perfect, need to look into shipping though.

Would any store carry these by chance?

[Transmogrifox]

P722-7R  is your man

[BAM]

great thanks alot!

now, how do i find which one is the P722-7R...?



:?  yeah.....*sigh*

[Transmogrifox]

Just hold them all under a lamp and measure the resistance.  It will be the one with the lowest min resistance.  

It doesn't take a terribly long time to assemble these LED/LDR devices, so you could just make a few and find which range sounds the best.  

I hope this works out well for you.  Take care

[BAM]

Thank you so much, you have been a HUGE help. I'll post pics of the final product. Thanks again!

[Bernardduur]

I used a 1k light, 300k dark and it works perfectly