What do I need for a dyi vactrol?

[dpaul_gtr]

Hi,
I'm thinkining of building a trem (the demeter tremulator sounds really nice), but i can't find that vactrol anywhere in Romania, so i have to build one.  Can someone tell me what kind of led and ldr should i use?
Thanks

[petey twofinger]

what little i know is this , a cds cell or ldr which is a  light dependant resistor , and an led CAN work .

you test the cds cell in light then darkness and select the one that gets closest to how the part that is called for responds to light and dark . so you would heve to look at the data sheet for the vactrol it calls for , get those numbers , then test out the cds cells at full brightness then dark , using the ohms or resistance setting on a multimeter .

i have seen folks say they had best results with yellow and green leds .

when i did this , i only tested by ear , i used a multi pack of cds cells i got from radio shack , the tiny one in the pack seemed to do fine . i forget the led i think i used a red 3mm .
what circuit is this for , some circuits are much more " forgiving " if you use a home rolled vactrol , some are much more picky from what i have read .

oops , its the demeter tremulator ...

i found this :

I'd also encourage anyone building one of these to just build your own vactrol. I got a VTL5C1 and one I built with a 5mm red LED and a LDR and I notice no difference between the two in the time it takes for me to change them out. " so yeah , perhaps google around and see if others have had success fabricating vactrols to replace that part number , and what parts they used .

[dpaul_gtr]

what little i know is this , a cds cell or ldr which is a  light dependant resistor , and an led CAN work .

you test the cds cell in light then darkness and select the one that gets closest to how the part that is called for responds to light and dark . so you would heve to look at the data sheet for the vactrol it calls for , get those numbers , then test out the cds cells at full brightness then dark , using the ohms or resistance setting on a multimeter .

i have seen folks say they had best results with yellow and green leds .

when i did this , i only tested by ear , i used a multi pack of cds cells i got from radio shack , the tiny one in the pack seemed to do fine . i forget the led i think i used a red 3mm .
what circuit is this for , some circuits are much more " forgiving " if you use a home rolled vactrol , some are much more picky from what i have read .

oops , its the demeter tremulator ...

i found this :

I'd also encourage anyone building one of these to just build your own vactrol. I got a VTL5C1 and one I built with a 5mm red LED and a LDR and I notice no difference between the two in the time it takes for me to change them out. " so yeah , perhaps google around and see if others have had success fabricating vactrols to replace that part number , and what parts they used .

.

Thanks for the info, man! I've looked up the topic on google and i've found anything from infrared to white leds but, come to think of it, leds are cheap so i'll try a bunch of them and see what happens.
Oh, and by the way, i've found out why i can't find vactrols around here: the european union (the same guys who tried to put a ban on curvy cucumbers and straight bananas - i'm not kidding) have banned the use of devices that contain cadmium (sorry for the off-topic ).

[petey twofinger]

i THINK what you will find if you experiment a bit is that the cds cell will have a much greater effect on how it performs as opposed to the led .

http://ampgarage.com/forum/viewtopic.php?p=199112&sid=360996b8855afccf7856f3730e153837

[greaser_au]

here is an appropriate & potentially useful thread from a few months back:    http://www.diystompboxes.com/smfforum/index.php?topic=95269.0

I sequestered a piece of 'protective' black tubing from the packaging of a glowstick necklace for this sub-project!   (the black tubing that protects the small-diameter glowsticks from being 'broken' in transit)

david

[Mark Hammer]

Many LDRs will have a range of light wavelengths that they are most sensitive to.  They are not completely INsensitive to shorter and longer wavelengths, but it is usually a good idea to know a little bit about the LDR's "ideal" wavelength so that the LED can be best-matched to make the LDR behave according to specifications.

So, for example, this one specifies the wavelength of maximum sensitivity as 650 nanometers: http://www.taydaelectronics.com/resistors/photoresistors/photo-conductive-cell-resistor-ldr-650nm-radial-ke-10720.html

650nm is roughly orange ( http://en.wikipedia.org/wiki/File:EM_spectrum.svg ), so you'd want to use an orange LED for this particular LDR, rather than red or green or blue.

As I say, it is not that general purpose LDRs are very fussy about what light they receive, but a better match should improve performance.  Know your LDR!

[samhay]

Mark is mostly right, but 650 nm is actually quite deep red. For the LDRs he posted, I would imagine you will get the best result with a red LED. As always, a little testing goes a long way.

The wikipedia LED page has a nice table with LED output wavelengths (and a simpler table just above it):
http://en.wikipedia.org/wiki/Light-emitting_diode#Colors_and_materials

[alparent]

What about matching the lights on / lights off resistance? And the speed of those changes? Does it matter?

[Mark Hammer]

Mark is mostly right, but 650 nm is actually quite deep red. For the LDRs he posted, I would imagine you will get the best result with a red LED. As always, a little testing goes a long way.

The wikipedia LED page has a nice table with LED output wavelengths (and a simpler table just above it):
http://en.wikipedia.org/wiki/Light-emitting_diode#Colors_and_materials

You're absolutely right.  hadn't counted off enough hash marks on the vernier.  Thanks for catching that.  In my defense, I had just come back from some very uncomfortable tests at the hospital! (Don't worry, folks, absolutely nothing serious)  Silly staff left the darn catheter in my arm.  Didn't notice it until lunch.  Now I have to go around with it for the rest of the day until I can go to a walk-in clinic.

[smallbearelec]

Hi--

If you want to order from within the EU to avoid problems with Customs and keep shipping down, try Musikding or Banzai. I notice that they stock various CdS opto devices, so clearly they are still being sold. If you are OK with ordering from across the pond, the "F" model of this photocoupler:

http://www.smallbearelec.com/servlet/Detail?no=1296

works well in DIY trems. If you want to roll your own, try a Silonex NSL-5542 with a high-brightness red LED:

http://www.smallbearelec.com/servlet/Detail?no=357
http://www.smallbearelec.com/servlet/Detail?no=334

For ideazz for a great trem:

https://www.smallbearelec.com/Projects/TremBear/TremBear.html

Regards
SD

[samhay]

What about matching the lights on / lights off resistance? And the speed of those changes? Does it matter?

If you are trying to match an LED/LDR combo to a specific vactrol spec'd for a circuit, then trying to get the on and off resistance in the same ballpark is a good idea. As long as you can get enough of a resistance swing between the light and dark states (between about 10k and 1M is not unreasonable)  then you can usually tweak to make it work. Tremolos are usually more forgiving than some other applications too. I don't think you can do much about the 'attack' and 'recovery' rates - LDRs are just relatively slow - but this can sometimes work in your advantage.

Mark - no worries. I do quite a lot of optical spectroscopy, so it was nice to be able to put my day job to use for once. Hope your arm didn't suffer any ill effects from yesterday's adventures.

[duck_arse]

I've got a 77 page pdf "Photoconductive Cells and Analog Optoisolators (Vactrols®)" from the PerkinElmer Optoelectronics people, a link to which I can't find/ too slow/ won't load, which has all the ins and outs of their cds and vactrols, including spectral maps and sensitivity data. it should answer a few of your questions, dpaul_gtr.

seeing as it is usually their product numbers being bandied about, I'm surprised more people don't look them up.

[Lurco]

Try this: http://www.datasheetcatalog.org/datasheet/perkinelmer/VT500.pdf

[duck_arse]

well spotted. I just checked the last page of my pdf, and it does indeed say blah blah www.datasheetcatalog.org.

[dpaul_gtr]

Thanks everyone for the input and advice!

I just wanted to say that I've finally managed to start working on the trem (I've been kinda swamped with schoolwork and other stuff lately, that's why it took me almost a month ).
I have bought a LDR and a high-brightness 3mm white LED and I've rolled my own optocoupler. It's ON resistance is around 200-250 ohms, and it's OFF resistance is higher than 20 megs (I'm not sure how much higher - my cheap DMM stops at 20 MOhms), which is better than I've hoped for and I reckon it should work just fine. I don't know what type of LDR it was, the guy at the store had like 6 or 7 of them in a small bag, without any labels, and I've measured them - some wouldn't go lower than 100k when subjected to light, some wouldn't go higher than 600k in darkness.

Hi--

If you want to order from within the EU to avoid problems with Customs and keep shipping down, try Musikding or Banzai. I notice that they stock various CdS opto devices, so clearly they are still being sold. If you are OK with ordering from across the pond, the "F" model of this photocoupler:

http://www.smallbearelec.com/servlet/Detail?no=1296

works well in DIY trems. If you want to roll your own, try a Silonex NSL-5542 with a high-brightness red LED:

http://www.smallbearelec.com/servlet/Detail?no=357
http://www.smallbearelec.com/servlet/Detail?no=334

For ideazz for a great trem:

https://www.smallbearelec.com/Projects/TremBear/TremBear.html

Regards
SD

That Tremulous Bear really does looks interesting, and very versatile. If you don't mind me asking, could you tell me approximately how much would it cost to ship to Romania?