Heat shrinking LED/LDR combos

[Govmnt_Lacky]

Working on a project that calls for a few LED/LDR combos. I have already put them together and used black heat shrink to keep them nice and dark when the LED is off. After looking at them together, I am left wondering if the heat shrink will impede the LED from fully illuminating the LDR.

Anyone have experience with this? Has anyone experienced problems with the resistance range of the LDR when using heat shrink?

[Liquitone]

I can imagine it would indeed so that.
I once pulled apart a LED/LDR combo from an EHX pedal and they put the LDR/LED inside a sort of semi-rigid tube made from polyester-cloth before putting them inside the heat-shrink, to prevent the problem you just described.

[artifus]

haven't done any heat shrinking here but what i do use is black drinking straws. something which is not talked about much here is led/ldr proximity...

[Liquitone]

The one I pulled apart had the LDR and LED touching each other under the heat-shrink.

[Govmnt_Lacky]

The one I pulled apart had the LDR and LED touching each other under the heat-shrink.

This is how I have my combos set up. tip of LED touching face of the LDR.

I noticed that the heat shrink collapsed and formed around the dome of the LED and is semi-inhibiting the face of the LDR. I know the LED will light up the LDR... I am just wondering if the decreased facial area of the LDR, due to the heat shrink, will effect the resistance range.

[Liquitone]

I think it will, and I think that's why the EHX Opto-thingy (from The Worm) had a tube around it before putting it inside the heat-shrink.

[Govmnt_Lacky]

@Liquitone

Thanks for the confirmation and opinion.... SIGH****  Now I gotta take them all out and cut off that DAMN heat shrink! 

@artifus

Tell me more about the drinking straw idea PLEASE! 

Will a typical drinking straw fit a 5mm LDR?

[Jdansti]

If you use a rigid tube with heat shrink in the outside of it, do you use epoxy or some other adhesive in the ends of the tube to hold the parts in place?

[gritz]

Yeah, intuitively all of the light from the LED has to hit the LDR evenly across it's entire active area. This would suggest that a "pinched, waisted" heatshrink join would be a_bad_thing and that encasing in a tube (maybe even one with a reflective internal surface) would be the way to go. A short length of aluminium tube with heatshrink on top? Or maybe a strip of thin card with shiny tape on one side, under the heatshrink.

"Touching, or not quite touching?" Should be easy to work out with a meter and a few seconds of one's time.

[artifus]

just fill your pockets next time you're at the bar or at the counter of your local fast food outlet. cut to size and experiment. i've had different diameters from different sources. as i've had different ldr's from different sources. the main pro over heat shrink is being able to adjust ldr/led proximity post soldering.

Tell me more about the drinking straw idea PLEASE!  

Will a typical drinking straw fit a 5mm LDR?

*edit* something i've thought about but not experimented with yet: using cut and drilled bits of glue stick as diffuser? *glue stick - as in what you use in a hot glue gun*

like this but using a glue stick instead of a perspex rod and a led instead of a lamp:



from: http://sound.westhost.com/project45.htm

[Govmnt_Lacky]

If you use a rigid tube with heat shrink in the outside of it, do you use epoxy or some other adhesive in the ends of the tube to hold the parts in place?

I could ASSume that if you use a rigid tube and cut it to the right length, there would be no need to use adhesive. If it is true 5m ID, then the part fit "should be" tight enough to keep it together. Then again, you would need to find 5mm ID BLACK tube  

The heat shrink would probably not collapse around the ends well enough anyway  

[Jdansti]

I guess you wouldn't have to rely on a press fit or adhesive as long as you can easily make the necessary bends in the leads in the proper places and the parts are soldered into place.

It seems that if the heat shrink that extends beyond the tube would not shrink up tight enough to hold the leads in place.  I kinda like having my LDR/LED as a unit that can be handled and soldered into ace as a single unit. It seems that this would work for me:

1) Place the components inside the drinking straw.
2) Place a small dab of hot glue or epoxy in the two ends of the straw where the leads stick out.
3) Enclose the whole thing with black heat shrink.
4) Bend the leads as necessary to fit on the board.

[gritz]

Not making the entire assembly "light tight" can send your expected meg-Ohm dark resistance up the Swanee when you engage the pedal and a bit of light from the back of your indicator LED leaks into the enclosure. Been there, done that. 

[artifus]

i'd assumed light proofing the assembly was taken for granted given the nature of ldr's. apologies if that was not made obvious.

[Govmnt_Lacky]

i'd assumed light proofing the assembly was taken for granted given the nature of ldr's. apologies if that was not made obvious.

What i dont understand is that SO MANY pedals that I have seen have the LED/LDR out in the open 

No heat shrink, tubing, or enclosing at all. Just the LED butted up against the LDR. Is it because when the enclosure is sealed up it shuts out the ambient light?

[Liquitone]

If you use a rigid tube with heat shrink in the outside of it, do you use epoxy or some other adhesive in the ends of the tube to hold the parts in place?

The one I pulled apart didn't have any adhesive, the tube fitted very tightly around the LED and LDR and the heat-shrink kept everything in place pretty good.
But I must add seeing the top picture, (those are the LDR's I pulled from the photo-coupler) they are of the enclosed type making it the same diameter as the LED.
The tube had a inner diameter of 5mm and the length fell just inside the wider rims of the LDR and the LED, I can imagine a non-enclosed LDR would need some help staying in place.

i'd assumed light proofing the assembly was taken for granted given the nature of ldr's. apologies if that was not made obvious.

What i dont understand is that SO MANY pedals that I have seen have the LED/LDR out in the open 

No heat shrink, tubing, or enclosing at all. Just the LED butted up against the LDR. Is it because when the enclosure is sealed up it shuts out the ambient light?

I kept them in the open on my builds;




I kept them open because I used these metal LED-bezels with a plastic holder on the inside that doesn't let any light through, and with the enclosure shut I figured I didn't need to put the LDR/LED assembly inside a heat-shirk tube.
Also on the lower picture I used a Lamp instead of an LED, and it got so hot that the heat-shrink sort of started to melt and get all sticky.

[Jdansti]

i'd assumed light proofing the assembly was taken for granted given the nature of ldr's. apologies if that was not made obvious.

What i dont understand is that SO MANY pedals that I have seen have the LED/LDR out in the open  

No heat shrink, tubing, or enclosing at all. Just the LED butted up against the LDR. Is it because when the enclosure is sealed up it shuts out the ambient light?

It's all about keeping stray light out. As Liquitone says, he uses a LED bezel that doesn't allow stray light into the enclosure. It seems that you could potentially have a problem with open style jacks. [Edit-Unless of course there's a cable plugged into them!  Duh!  ] The other thing is if you have multiple optocouplers operating on different cycles or brightnesses, you could have some crossover light issues.

I kept them in the open on my builds;

I kept them open because I used these metal LED-bezels with a plastic holder on the inside that doesn't let any light through, and with the enclosure shut I figured I didn't need to put the LDR/LED assembly inside a heat-shirk tube.
Also on the lower picture I used a Lamp instead of an LED, and it got so hot that the heat-shrink sort of started to melt and get all sticky

Are the three optocouplers in your photo all operating in sync?

[Liquitone]

Haha!,. yeah I had the same brain-fart with the open jacks when I built it.
yeah those 3 LED's are running in sync.
I made advantage of stray light once. I had build this tremulus lune with 2 lfo's you could switch between or kept them both running at the same time.
The LED of each LFO both controlled the one LDR  of the signal-path, this way I could create all sort of weird tremolo rhythms. different speeds, waveforms, depths all mixed together.

[Thecomedian]

well, in a pinch, heatshrink them separately, and then combine and heatshrink them together?

[armdnrdy]

One thing that may help eliminate the issue of shrink tubing wrapping around the LED is to file the front of the LED flat.

I crazy glue the LED and LDR together before I shrink tube it. Filing the LED serves two purposes: it's much easier to get a good bond with a flat surface rather than a round one, and the overall footprint of the DIY optocoupler is reduced.

When applying heat to the LED/LDR combo, concentrate on the ends to seal the component leads and less on the junction of the LED/LDR.