Enclosures, paint and heat dissipation.

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I wonder if something like clear Polyurethane would make a difference?

-Lasse

Reply to
langwadt
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man

the case.

B transmitter.

it kinda negates the point of a sleek slim computer if you have to put a processor fan next to it to use it ;)

-Lasse

Reply to
langwadt

Most organics are pretty opaque (high e) at thermal wavelengths, but I don't know about that one. Black plastic garbage bags are almost transparent!

John

Reply to
John Larkin

That's interesting. I was buying 'black' cloth to block near IR light ~800nm. Black 'plastic'* cloth was no good, where natural canvas worked great.

George H.

*think velour or plush velvet

Reply to
George Herold

Hi, George. I am looking at quickly pulling together a papertape reader. Something that will transmit to a virtual COM port via USB. Already have most of it done, due to a different project I completed a month ago or more -- this would simply be a 'front end.'

Anyway, I ordered up some standard LTR-4206 (not the E part with the dark blocking plastic) phototransistors from jameco because they had them 'dirt cheap' (0.75 cents each.)

(I am still going to play around with using simple LEDs as detectors, but I didn't have any phototransistors other than two very old ones.)

Anyway, I was curious about the paper in the paper tape. So I looked up transmission by wavelength for paper. (If you know of a good published paper on paper transmission and in particular the paper used in 1970's style paper tape, by all means tell me!!) I found that in the visible it's fairly opaque. But in the IR transmission rises and diffusion declines. So it gets a little more problematic for me, I think.

High emissivity is associated with high absorption (for obvious reasons.) Roberto's comment about finding some comments about high emissivity in the IR for organic pigments makes me wonder, as being as ignorant as I am right now about these things I'd tend to think that what I found recently about paper (which _is_ organic) flies just a little bit in the face of having higher emissivity in the IR.

But it's probably just my ignorance and these two facts are not in contradiction.

Anyway, I expect to find out soon. The LTR-4206's have been shipped out this morning and I may see them this week. That plus some testing with various LEDs as detectors in a micro setup will tell me what I'd like to do in terms of finishing this project. (Found a cache of old paper tapes from "back when" and I'd like to transmit them into the computer as archives.) Just in case you are interested, I plan to test out this idea regarding using the LEDs as detectors:

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Also suggests some interesting thoughts on low speed, bi directional, lost cost (zero, essentially) transmission using a simple LED. Looks like fun to do.

Jon

Reply to
Jon Kirwan

you need an audio file to play that goes 'ka-chunk,ka-chunk,ka- chunk,ka-chunk,ka-chunk'

we sometimes would 'butterfly' tapes instead of rolling them. make a figure eight between thumb and pinky - like an infinity symbol.

good times.....good times

Reply to
1 Lucky Texan

I had wired up my own "back in the day." I couldn't afford anything like a punch... probably would still blanche at the cost today. And at the time, I couldn't afford a reader, either. So i built a hand-pulled one using 9 detectors and an optical source and pulled the tapes through by hand. I still plan on doing something quite similar, except now I can use a microcontroller and some techniques that weren't available to me, back then.

There really wasn't much sound from hand-pulling. So I can live without the sound effects.

By the way, can still read an ASCII tape fluently by eye.

Yes, I remember. I didn't like the folded situation, though. I used, and still have, those clear cylindrical tape containers with the simple lids.

I think I might have a tyvek tape or two. I see that the stuff is still available (as is paper tape) but costs 10X the paper, about as it did back then.

Yes. Damn, if only I could have latched onto and kept an ASR-33 or even a KSR-35, and functioning. Current loop,

4-20mA, but I can convert that easily today.

Jon

Reply to
Jon Kirwan

That is correct you need to know how the paint behaves for thermal IR. Some of the better research on this in the open literature is for observatory domes which in the old days were as white as possible to minimise daytime heat load but now are mixed with other components.

Their problem was at night the dome surface would supercool because of radiative losses to the sky and cold air would pour into the dome through the slit producing local turbulence - which is always bad.

There is a lot of research for novel pigments in fire protection paints at the moment that reflect thermal IR and slow the ignition of painted wood (other flammable materials).

Your ideal would like the astronomers of old be a perfect white paint in the visible and near IR that is black for thermal IR around 10um.

One thought is that you might be able to get away with something as simple as black dry marker pen over the hotspots (assuming they are 50C or more which is when radiative losses become really important).

Test it on some bit that won't matter first. Some anodised type finishes can end up permanently disfigured by pens that will wipe off a whiteboard - don't ask how I know this ;-).

Regards, Martin Brown

Reply to
Martin Brown

On a sunny day (Tue, 23 Aug 2011 15:20:47 -0700 (PDT)) it happened " snipped-for-privacy@fonz.dk" wrote in :

Dunno, I have a fan on my Nvidia graphics card that adds maybe 1 cm to the height. Just a bit of airflow along the outside of a cabinet makes ALL the difference. And it would keep the look from the front intact.

Reply to
Jan Panteltje

Hi Jon,

"But it's probably just my ignorance and these two facts are not in contradiction."

Well we are equally ignorant then. I have no idea why black canvas was better at blocking NIR (N=3Dnear), than manmade materials. I guess the lesson to learn is never assume that behavior in the visible extends to other wavelengths.

Many moons ago we used sheets of white paper as attenuators for a FIR (F=3Dfar, lambda > 10 um) laser. Each sheet blocked something like

20-30% of the light. (but don't quote me on that number.) So I can at least confirm the white paper transmission at long wavelengths.

BTW 3M black electrical tape is great at blocking light out to at least ~1 um. (A piece over a silicon photodiode blocks almost everything.)

George H.

Reply to
George Herold

Keep an eye on sleazebay. Not too much there at the moment but it does tend to be the default place old junque shows up (sometimes desperately overpriced, but you learn to let those slide, or grit your teeth and pay, in which case it may not have been all that overpriced after all...) I guess there is something described as a model 33 teletype (searching on teletype rather than paper tape), but it looks like only the middle part of what you want.

On the other had, paper tape reader units off old cnc machine tools are more common there.

Also several standalone PTR units of various types (GE, Barudan, K&T)

--
Cats, coffee, chocolate...vices to live by
Please don't feed the trolls. Killfile and ignore them so they will go away.
Reply to
Ecnerwal

Shipping an ASR-33 will kill you. I remember how hard it was getting mine into the dumpster..

Reply to
Spehro Pefhany

It helps to unplug it, first. ;-)

--
You can't have a sense of humor, if you have no sense.
Reply to
Michael A. Terrell

Emissivity of average equipment enclosures is not very meaningful. Equipment that runs reasonably near room temperature exchanges nearly all the heat by conduction/convection, not radiation. Now, if you are talking about major heating elements, then radiation does enter the picture. But, for electronic enclosures where you can put your hand on the box, coatings for the most part make no difference at all. Stirring the air inside the box so the internally-generated heat warms the entire box's inside can be a big help.

Jon

Reply to
Jon Elson

Yeah, but I like feeling that I grasp theory, too. When I get information that questions my grasp, .... Anyway, no matter what.... test, test, test.

Yeah, I was looking at curves that went into the NIR, only. Maybe a micron? It was mostly dealing with visible, because that's what they were discussing for the most part. They just happened to show a tail in the NIR. It had gone from strong blocking in the blue to perhaps 40% transmission at 1 micron.

But paper is so different, too. Fiber thicknesses, density, layers, and so on. I think I read it is usually at least 10 fiber layers deep. Anyway, papertape is a little different in appearance than stock paper and may have significant differences. I'm going to have to test at various wavelengths.

Interesting thing is that at 0.1" between holes, I can't use anything like the 5mm or 3mm bodies of typical LEDs and photo transistors designed for throughhole. Unless I grind the daylights out of them to reduce thicknesses. I'm considering other ideas, since I also don't want cross-talk from pressing closely a bunch of plastic bodies with ground surfaces. Standard vectorboard with plated throughholes looks like an option, but I'd probably need fiber optic wire of the right diameter (haven't measured that, though I could always order what I want, I suppose) to fit those holes. That would allow me to basically place the detectors anywhere. (Could also drill an aluminum block for same purpose.) I'd use a bright source above and to mount the fibers on the LED bodies I'd hold by hand and observe where the light targets and then glue them down to the LED/photobjt body and hold until dry?

This optical head is not entirely going to be easy, if I don't use SMT. The SMT path is nice. LEDs are tiny and can actually be spaced at 0.1" even when used long-wise, let alone along the thin width. But then I have to go get those

-- I have zero SMT LEDs in my collection. Plus make a board with spots for nine of them.

And I still have to work out what is going to do well with this paper, wavelength wise and detector wise. The rest is all going to be a piece of cake.

Hmm. I may think about that as a barrier between detectors if I don't go the SMT route.

Jon

Reply to
Jon Kirwan

Well, I noticed that the description of the punches mentioned that the tape was "oiled paper", which would affect light transmission quite a bit. Before glass was cheap, oiled paper (among other things) was used for windows by the less wealthy, since it transmitted more visible light than plain paper (shedding water was likely also good...) Presumably tape is oiled to keep the punches happy and/or cut down on dust.

--
Cats, coffee, chocolate...vices to live by
Please don't feed the trolls. Killfile and ignore them so they will go away.
Reply to
Ecnerwal

t

If you alternated some small front-surface, 45degree mirrors, you can double the 'pitch'/spacing required for the detectors. 2 staggered rows if you get the idea.

Reply to
1 Lucky Texan

It sounds like you may be rather further along on this, but if I were tasked with reading paper tape today, particularly a one-off application, I think my first inclination would be to use a camera of decent resolution, and pull the tape past that at a relatively constant rate. Add a little lighting, a contrasting background so the camera can see the holes, and then processes the data stream out of the video.

Actually that would be my second inclination - a friend of mine actually has a couple of ASR-33s in his basement (and one of them was actually hauled out and operated, four or five years ago). And I probably have an RS-232/current loop converter somewhere in the parts bin.

Reply to
Robert Wessel

Yeah. I think I have an easier method, right now. I've used a metal washer (convenient only, not because it is a washer) that is about 2" diameter and wide. I used a piece of vector board for my 0.1" spacings and drilled through each of 9 holes, but two rows for a total of 18 holes. I then milled out the span between adjacent holes making 9 slots. I then ground the sides of 9 3mm LTR-4206 phototransistors so that they would neatly fit in. These will be glued (haven't done that yet) into the holes and let dry. Once that is over, I use a dremel and a grind stone to flaten the tops down to the surface. Then I cut the metal rectangle out of the washer, polish and nicen up the edges and mount it into a similarly sized depression I cut into a block of hardwood. Large flat surface, over which I mount a polished bit of clear plastic over the area to keep the papertape near the detector tops. Then the electronic testing begins and I figure out and test a reasonable circuit.

And I hope I don't run into problems dicerning when a hole is present.

Turns out a friend of mine still has his Remex reader. 120cps full speed, but allows 'step mode.' I might adapt that one, too, for USB. (It hooks up to a 68020 PIO chip of some kind, right now, and was used with an Altair 8800 system and is pretty dusty right now.)

This is kind of fun. Too bad I don't have proper tools. But I'm getting by okay.

Jon

Reply to
Jon Kirwan

I am looking around for an ASR-33. :) Tell your friend if he's not going to make that stuff useful, to consider the idea of parting with it so someone else can.

I don't like the camera idea... It's not necessarily a one-off (I do have friends who are interested in the results.) I don't want to have to use a controlled pull rate. And I'm doing this in part as a project to teach my son more about design and construction as well as software. Just taking a bunch of photos that are stitched together in some fashion and then analyzed will take more development time, anyway. This is going very fast, already. I just started about an hour ago dilling holes in a washer and grinding the detectors. The read head will be complete in less than 3 hours' time, at this rate. I already have almost all the software done from a different project that accepts parallel port data and strobe and sends it into the USB port that I started and finished quite quickly, more than a month back. With the sprocket hole being the strobe, it's almost a dead match for this, given a little bit of signal conditioning on the read head. And I can handle thousands of characters per second on the other device, already -- way more than I can ever need here. I like leveraging other work

-- it also teaches lessons.

Jon

Reply to
Jon Kirwan

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