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Paper Tape Readers

NeXT

NeXT

Veteran Member
Joined
Oct 22, 2008
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Location
Kamloops, BC, Canada
Being fed up with how much standalone readers cost I'm building my own. The basic idea works like this:

Diagram.png


The phototransistors are arranged in a line and each one can see through a hole in the perfboard. These hole spacing is identical to that used on regular 8 hole paper tape.
Underneath the paper tape is a block of LED's that shine up and trigger the phototransistors when a hole is present for that bit in the tape.

This could also be reversed where the light source is above and the bed of phototransistors is below. Might be more handy if I could somehow hinge the top for easier tape loading. The whole final assembly is then soldered to another perfboard with the rest of the logic.

So far this is what I have done.
CGS_0087.jpg

CGS_0089.jpg


From there I run into a snag. I don't know how to keep the paper tape aligned. It will need some sort of guides to prevent it form shifting to the left and right and once they are fitted they can't move.
CGS_0091.jpg


The other issue is the LED block. It has to sit in between the perfboard sandwich with the guides and the paper tape. I don't trust it having enough light to go through another set of perfboard holes. It can't be used as part of alignment with the paper tape as it's shifted to one side of the tape by almost 2mm.
CGS_0090.jpg


Any ideas?
 
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Now I'm wading into waters where I've never been.. but do you need a LED block? Wouldn't it be sufficient with a transparent panel of some kind (to press on the paper tape to help with the alignment), and just a single, bigger light above? Or in any case I guess the point is to have that transparent board on the light side of the paper tape. So that last picture would have a transparent panel/feeder between the light and the paper instead of the LED block currently pressing directly at the paper tape.

-Tor
 
Tor said:
Now I'm wading into waters where I've never been.. but do you need a LED block? Wouldn't it be sufficient with a transparent panel of some kind (to press on the paper tape to help with the alignment), and just a single, bigger light above?
Click to expand...

That's one way to do it -- that's how the Oliver Audio OP-80A works. Most commercial optical readers use an individual light source for each transistor, whether it's a discrete bulb or a bundle of optical fiber fed from a single source. Personally, I'd probably pick the fiber route, fibers are easy to stuff into perfboard holes and glue into place.

One thing to keep in mind about your light source: it must be either a very slow source (incandescent) or it must be fed from a well-filtered DC supply. While getting an OP-80A up and going recently, I discovered that non-incandescent lighting had enough AC flicker (including bulb-replacement LED devices) to produce false readings, especially false "data available" triggers from the sprocket hole.
 
I'd be tempted to use a "festoon"-type tubular incandescent auto lamp. More than enough brightness and enough thermal lag to mask any power supply ripple.
 
Chuck(G) said:
I'd be tempted to use a "festoon"-type tubular incandescent auto lamp. More than enough brightness and enough thermal lag to mask any power supply ripple.
Click to expand...

Really? I would of thought those would get too hot. Well I can make modifications to use that instead bus still, what would I use for alignment?
 
For alignment, I'd probably assemble a "sandwich" of a top sheet of clear acrylic, and two pieces of sheet metal (brass might be good) that are spaced just a smidgeon over the width of the tape under that, with your protoboard under that. Relieve any sharp edges. Thread the tape in the space between the acrylic and your protoboard. That should keep the tape flat against the protoboard and aligned correctly. You can get brass sheet in varying thicknesses from your local hobby store, who should have a K&S display. Alternatively, you can purchase shim stock at your local auto parts store or tool supply otufit.
 
Slightly o/t, but the "Colossus" tape readers have a light source behind the tape & a lens in front to project a magnified image of the tape onto the row of photomultipliers behind (obviously photomultiplier tubes are a little more than 0.1" across!) - just another good way of doing it.
 
NeXT said:
The phototransistors are arranged in a line and each one can see through a hole in the perfboard. These hole spacing is identical to that used on regular 8 hole paper tape.
Underneath the paper tape is a block of LED's that shine up and trigger the phototransistors when a hole is present for that bit in the tape.
Click to expand...

Hi NeXT,

I always wanted to do this! I missed my chance to get one of those Oliver Audio OP-80 so many years ago, and they are now quite rare.

Anyway, what is the part number of those photo transistors? Are they available at Jameco or Digi-Key or Mouser?

Thanks,
smp
 
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I built the optical block with a thin sheet of transparency on top and on the bottom. The sides were made out of card paper used in picture framing. The whole thing was then bolted together with nylon bolts and nuts.

CGS_0092.jpg

CGS_0093.jpg

CGS_0094.jpg

The alignment IS a little off but I'm going to hope that works well enough, otherwise I just need to tear it apart and recut the guides.

I decided that the best mounting method will be to have the block mounted to the logic PCB with the lamp underneath and a ribbon cable connecting the transistors to the other board. I gotta buy more nylon bits.
CGS_0095.jpg

CGS_0096.jpg
 
Okay, new problem.
Either the phototransistors are extremely sensitive, this is a very effective bulb or my logic probe is playing with me. When have the bulb's power cranked down to 3v the phototransistors are stuck low (light striking the phototransistors = LOW TTL signal = the light on my probe goes out) when you pull a tape through. If I slowly back the block away from the light I have to pass six inches before the phototransistors go high again. I have to drop the voltage way the hell down to 2v before I can get the phototransistors to behave and by then they're stuck high and I can't kick them low with the lamp with the holes in the tape. It's either no tape or tape inserted.
Yet if I turn on my fluorescent table lamp and put it up to that (or even my LED flashlight) it won't trigger them until I'm about an inch away
 
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Siemens HSFH309FA5

Edited: Oh for ****s sake. NOW I know why they are encapsulated in black. Yes the transistor is for between 380 and 1180nm but the dark packaging narrows what wavelengths can get IN to the phototransistor.
I'm essentially using the pickups for remote controls.
 
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Peak at about 900 nm--pretty well into IR. Well, that lamp is just too bright in that range. Try a smaller (incandescent) lamp. A couple of IR LEDs might do the trick.
 
Well ten 940nm LED's can be sourced for $3 but it will take until the middle of August to arrive. Don't think I have much of a choice now though considering I really don't want to redo that top PCB.
 
Just use one or two LEDs and position them somewhat farther away so that all holes are illuminated. Or just use a small lamp, like that in a night light. Or take that festoon bulb and drop the voltage way down.
 
I had to drop the festoon down to 2v and it was still unreliable. I have a bunch of small 3mm red LEDs that were working far more reliably but I only had five and they wern't good enough to serve multiple holes at once so I'll pay the $3 for more LED's because they aren't breaking the bank unlike the $7 festoon bulbs I'm returning....

While that's off to the side while the parts are int he mail would anyone recommend a place to lookup how I can then convert the 8-bit data stream into RS-232 serial? I'm seeing a fair number of projects on Youtube but nobody seems to mention how they converted it into a serial output. Some are using microcontrollers and others a half dozen blurry IC's. Best I can think of in a block diagram is:
Code: 
[buffer] -> [address decoding] -> [ROM table] -> [shift register] -> [serial output]
Stuff like PIC chips, EPROMs and MAX232's are readily on hand here. I had a brainstorm that perhaps the finished unit can fit in the expansion keypad knockout on my LA-120 and a switch can toggle the system between terminal I/O and paper tape input.
 
I'm trying to understand why you think they are too expensive. You can get a facit highspeed paper tape reader surplus for about $50-75. At that price they usually are parallel. You can use a simple latch circuit and hook them up to a parallel input port or there is instructions here on how to make a converter http://juliepalooza.8m.com/sl/remex.htm

I actually have my decitek high speed reader setup to be both parallel and serial since I run my terminal at 1200 baud, the parallel is faster to load basic on the altair. It loads at 600cps, but it cost a little more than $50 for a vintage reel to reel decitek that works (usually the motors need new brushes) though there are a few 200cps disk/paper tape combo ones on eBay for less than $100 buy it now, that could be fixed up if they don't work(decitek is still in business so you may be able to find schematics. I found the ones for my reader and its an older one (1970's)

Cheers,
Corey
 
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