A good method for encasing LED/LDR combos. (May sell some?)

[JKowalski]

There's a tiny 1/8 watt metal film resistor there for size comparison.

The coating that they are encased in is pretty much 100% lightproof, is not affected by the heat of soldering in normal conditions, and looks nice!

I just did this first test one today. I hooked up a voltmeter and a very well regulated lab power supply for the LED, and tested it. There is a superbright LED and a standard photocell from futurlec inside. With no voltage, I get infinite resistance on my meter. With maximum current through the LED, I managed to get the resistance down to 50 ohms. In static conditions, the resistance fluctuates by at most 1 ohms, and then only very rarely. I also tested the difference between a dark room and a bright LED flashlight directly on it, and there was absolutely no change in resistance.

I am probably going to make quite a few of these, and I was wondering - would there be a market for some of them? I would probably sell them for $1.50 or so. I could also sort matching sets, and do a range of different type LED/LDR's for various voltage/resistance curves and sensitivities based on your needs.


If anyone wants to copy the process at home, here's how I do it:

- Sand the LED flat as far back as possible (to reduce the size of the LED and give a nice flat round surface for bonding). They do sell flat top LED's, but they generally don't come in a wide range of choices and they are usually a bit more expensive
- Epoxy the LED to the LDR, coating it so remove all the gaps
- Bend the leads 90 degrees as much as possible to again reduce the size (this one isn't really a good example of it, there actually was heat shrink tubing on it first - it was one I just had lying around)
- Buy some Plasti-Dip (I think the other brand calls it Dip-It). It's a rubber coating that is used to recreate the grips on hand tools. Basically, it's a can of liquid-y rubber that hardens in the air. You just dip your LED/LDR combo in it, holding it by the bent leads. It dries as a pretty thin layer, but it's multi-coatable (the new coat actually bonds with the old coat to form a new single layer coating). I found that 3-4 coats is a good thickness. You need to wait 30 minutes between coats, and then 4 hours after the final coat for best results.
- Done!

The Plasti-dip stuff claims that it dries out pretty easily if it is not sealed in a airtight container (and the one they sell is definitely not airtight). I need to find myself one of those rubber sealed food jars at a thrift store to store the stuff, I guess. I have yet to see how well the product holds out...

[dmaher]

I have seen that sort of thing before...   think it might've been digikey or RS or some other massive distributor.

IIRC fairly expensive though.

What's the difference between this and say an optocoupler ?

[JKowalski]

I have seen that sort of thing before...   think it might've been digikey or RS or some other massive distributor.

IIRC fairly expensive though.

What's the difference between this and say an optocoupler ?

There really isn't any difference at all between these and optocouplers. They are optocouplers. I prefer doing it this way because It gives me excellent results and is much cheaper then most vactrols out there. The plasti-dip costs $6 for a pretty big can, the LED costs 10 cents, the photocell costs 25 cents, and the epoxy costs $7 or so for a decent size tube. It's also alot smaller and less akwardly packaged then the vactrols.

Each one totals at about 40 cents in material cost, though obviously it's more if you don't make use of the whole cans of plasti-dip and epoxy to make alot of them.

[Solidhex]

It would be nice if that stuff worked as an insulator. Stick some germaniums in there!

--Brad

[Taylor]

Where do you get photocells for 25 cents? Mouser doesn't have any, and Small Bear's are a dollar.

[.Mike]

Futurlec, I presume:

http://www.futurlec.com/Photocells.shtml

[Taylor]

Awesome, thanks.

[Ice-9]

Lots of mojo value, neat looking component. It takes a long time to make the component though

[Nasse]

I think they banned "plastidip" or similar here, some poisonous chemicals perhaps so it is not available but some other substitutes like few coats of black paint might do the job good enough

[Taylor]

FWIW, Lovetone left all their LED/LDR combos unshielded in all of their pedals. The flanger has 5 or 6 of the combos. People seem to like them a lot...

I've got a ton of NSL-32s that I use, but to be honest I prefer the uncovered type because having that flashing LED visible makes debugging easier.

[earthtonesaudio]

That's pretty smart!  Make sure you use a fume extractor or fan though, those fumes are noxious.

[JKowalski]

FWIW, Lovetone left all their LED/LDR combos unshielded in all of their pedals. The flanger has 5 or 6 of the combos. People seem to like them a lot...
I've got a ton of NSL-32s that I use, but to be honest I prefer the uncovered type because having that flashing LED visible makes debugging easier.

Yeah, I was considering possibly adding some kind of tiny window in the rear of the LED (like a miniscule dowel of clear plastic). I think I am going to try that on the next one I make, and see how it goes. It's obviously going to compromise the ambient light shielding somewhat, but I guess I have to see just how much.

Let me tell you though, the light shielding makes it alot easier to use on the breadboard!

Lots of mojo value, neat looking component. It takes a long time to make the component though

It does, but it's so easy to do it. You just dip it in the stuff (takes 10 seconds) then go about your day, come back in half an hour and do it again, etc. Then just let it dry overnight.

[mth5044]

That looks really good! Great job.

[Ripthorn]

I've always wanted a good excuse to buy me a can of plasti-dip.  It works great on picks so that they don't slip on you during a song.  As soon as I move and get settled, plasti-dip here I come.