Restoring Old Paper Tape
applecorey at optonline.net
Fri Jan 22 05:25:41 CST 2016
Another option is something like an op-80a where you can manually pull the tape across sensors making sure you don't damage it. Essentially a low tech version of what you guys described using a video camera.
The op-80a doesn't have a physical sprocket to break the tape, it uses the sprocket holes only for timing/triggering the character. Even if you don't have access to an one, they can be built pretty easily and the schematic is readily available on line.
I keep one around just for such a purpose, though I really should put a microcontroller together to bit bang the parallel to serial or a simple UART so that I can hook it up to a modern computer. It would remove the middle step of reading it into my sol-20 and then dumping it to my laptop.
> On Jan 21, 2016, at 9:46 PM, Charles Anthony <charles.unix.pro at gmail.com> wrote:
>> On Thu, Jan 21, 2016 at 6:21 PM, Jason T <silent700 at gmail.com> wrote:
>> On Thu, Jan 21, 2016 at 8:04 PM, Charles Anthony
>> <charles.unix.pro at gmail.com> wrote:
>>> For part 2, personally, I would take movies of the paper tape moving and
>>> doing image analysis to recover that data; this occurs to me because I've
>>> done a fair bit of image recognition software, so this solution may not
>>> feasible for all. If you sent me a sample movie, I would make a stab at
>>> writing some data recovery software.
>> I have heard of those approach and was thinking it may be a solution
>> in cases where the tape is too fragile (and that's pretty likely
>> here.) It would be well beyond my abilities but might make an
>> interesting project for you or anyone else with the skills.
> The general approach would be to have the tape backlit (on a piece of
> glass, with a light source and and diffuser underneath ) and guide block
> that the tape slides against so the holes move left-to-right but not up and
> down. The camera is set up so that the tape fills the image as much as is
> feasible. You start the camera, and slide the tape. Constant speed is not
> important, but avoid backing up.
> Grab a frame from the movie. Figure out the approximate pixel coordinates
> of the data and pin feed holes in the axis moving across the tape (eg, the
> 1 bit is about 24 pixels from the top of the image, the 2 bit is about 47
> pixels from the top, etc).
> Process the movie a frame at a time. Grab a column of pixels from the
> center of the image from top to bottom. Look at the pixels around where the
> pin feed is, decide if they are light or dark. If light, the a character is
> centered in the column. If not, move to the next frame. look at the pixels
> around where each data bit is, and decide if the are light (punched) or
> dark (unpunched). Write out that data. Skip frames until the pin feed
> pixels go dark, and then skip frames until it goes light again; that will
> be the next character. Repeat.
> The pin feed holes greatly simplify the process. This process is quite
> analogous to reading multi-track magnetic media with a timing track.
> Test on a known tape. Debug. Run over damaged tapes; data recovered.
> -- Charles
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