bonding LDR to LED

[bassmannate]

What's a good way to do this? I tried using cyanoacrylate (super glue) last night. It seemed to bond fairly quickly but remained wet/gummy around the joint for several hours. I left it over night and it was cured up this morning. While handling it this morning to try and get black heat shrink around them, they snapped apart. I really don't want to try that again. I think I have some clear casting epoxy but it takes quite a while to cure. It's  not the 5-minute stuff.

Any help would be appreciated. This is the last on-board component for an optical compressor and then I can start the off-board stuff and boxing it up.

Edit: forgot to mention I did flatten the lens of the LED a bit with some sand paper to get more surface area on the LDR to bond with.

[GibsonGM]

I don't bother try to actually "bond" them, bassman...what most people do is to get some heat-shrink tubing of the appropriate size, snug the 2 tightly together, slide the tube over and heat it.  It works well this way, at least for all the things I've used this method for (phasers, trems n stuff).

Maybe someone else has a different way, let's see if they chime in...

[bassmannate]

I don't bother try to actually "bond" them, bassman...what most people do is to get some heat-shrink tubing of the appropriate size, snug the 2 tightly together, slide the tube over and heat it.  It works well this way, at least for all the things I've used this method for (phasers, trems n stuff).

Maybe someone else has a different way, let's see if they chime in...

Alright. As soon as I find something to do with the baby that's sleeping on my chest, I'll try just using heat shrink by itself. Do I need to bother filling in the space behind the LED and LDR to block any stray light? It's going to end up in a closed box so I doubt there will be much opportunity for light to get to it at all anyway.

[peterg]

As GibsonGM said heat-shrink tubing is the way to go. Leave the tubing long enough to pinch the ends together around the leads.

[peterg]

bassmannate - you posted your reply just before my previous post. Pinching works to keep out the light.

[bassmannate]

Perfect! Perhaps I'll try pinching it shut while it's still hot and slightly sticky.

[GibsonGM]

I've used dark colored caulking to 'seal up the back', but I bet pinching it works too!     

[davent]

The double-walled with adhesive type heatshrink seals up really well if pinched while still hot.

[thermionix]

For assembling neon/LDR Fender tremolo optoisolators, I've used a dab of hot glue to hold everything together while heat shrinking.

+1 on pinching the ends while still hot and sticky.  (Ooh baby!)

[bassmannate]

Got it! Thanks guys!

[fraser]

hi folks-
im a stranger to most of you, but i have a query relative to this thread.

ive been tinkering with a magnavibe clone and an ldr/led setup in a delay modulation circuit.

the magnavibe is really subtle, so i tried a bunch of combinations, always shrinkwrapping.
but im finding i get the most 'wobble' if i dont cover the ldr/led at all, and have it all boxed up.
i wonder if its because the light bouncing around the box helps to modulate the resistance in a less predictable way.
im going to try adding reflective material to the inside of the box next.

doesnt seem to make a difference really in the delay modulation setup, but i havent really played with it much.

anybody have any thoughts on this? or am i just displaying signs of early dementia?

[Kipper4]

@Fraser
For the magnavibe I've found using a super bright clear 5mm led and 1M dark Ldr worked best for me. I rolled my own with a top hat led and pretty much made it like Bassmannate did in his photo.
Black heat shrink.
Welcome aboard Fraser

@Bassmannate
Personally I don't bother to put separate heat shrink around each leg of each led/Ldr
I use 6mm black heat shrink as you did and cut it 6mm longer than the componants butted together.
Hold them head to head in the helping hands heat up on all sides. Remove before it cools down and bend all legs down. It pays to pre plan the bending so the anode /cathode of the led are correctly orientated for my layout.
It makes the vactrol footprint much smaller.
If needs be I'm sure you could reheat for amendments.
Just being picky. Sorry.
You did a good job.

Edit. It's worth typing led Ldr into the search function here too. There's plenty of threads including a very nice test rig from Duck Arse, something about map your led Ldr

[TejfolvonDanone]

I haven't worked on any LED/LDR thing but maybe a reflective LED case might direct more light to the LDR.
http://www.conrad.biz/medias/global/ce/1000_1999/1400/1490/1497/149769_LB_00_FB.EPS_400.jpg

[fraser]

For the magnavibe I've found using a super bright clear 5mm led and 1M dark Ldr worked best for me. I rolled my own with a top hat led and pretty much made it like Bassmannate did in his photo.
Black heat shrink.
Welcome aboard Fraser

thanks kipper-
i used black shrinkwrap, and pretty much followed what everyone else did on that project-
i got the best results with a 5mm blue super bright-
but yeah, it sounds better without any wrap at all.

i tried all kinds of angles etc-
thus far, led pointing straight down at ldr, maybe 2mm away, no wrap gives me the most pronounced effect.

its all good, im really happy with how it sounds.
just trying to understand 'the why' really.

[Kipper4]

Probably to do with Ldr more than the led.
I'm no expert but I'd imagine Ldr manufacture tolerances vary quite a bit depending on the substrate.
When I've metered some Ldr that supposedly have a 1M dark resistance ,they go way over that.
This is probably not a very scientific way of testing ,just a Q and D method.
There are so many variables. I don't know what to blame.

[bassmannate]

Yeah i realized how silly wrapping the individual leads was after i wrapped the whole thing that pressing the leads together wasn't going to be an issue.

[PRR]

The LED should maybe light the WHOLE active area of the LDR. With the old large LDRs that usually was NOT nose-to-glass, but a little separation. Light the LED and look at the pattern as you vary the distance.

I must admit I never had shrink-tube handy. I do know the LEAST stray light can cause trouble in some circuits (I learned to work in near total darkness). Aluminum case looks dark inside but in real room light there is significant leakage around the edges. I liked little bent-up cardboard shields over my LED/LDRs pairs. I blackened them inside and out.

[GaryM]

Here's a coupling method I stumbled upon while doing a web search for optical compressor schematics. It ought to work just as well with an LED.

I usually just glue an LED and LDR together in a section cut from a black plastic ball point pen.

[pinkjimiphoton]

shoot, i've done it with just black electrical tape with some pretty awesome results.  if it's gonna be in an enclosure anyways, it shouldn't make that much diff.

my fav was the wobbltron build... actually, i never got that working so i did the bearfoot magnavibe instead. on that one, i used one of them gigantic water clear white ones about as big around as my pinky, and a bog standard ldr, no heat shrink or tape or anything, just pointed them at each other in the box, and it worked out great. in that build at least, the larger led gave it a lot more depth.

it's currently on tour in europe somewhere with my bro glenn guay. it's been on tour to newfoundland too. kinda cool!!