SHARP PHOTO-INTERRUPTER HELP  - Page 1
Forum section: electronics / repair

author: gooseEL34
author_rank: Regular Contributor
timestamp: June 23, 2015, 03:55:29 am
content: Hey allI have a MIDI footpedal used to switch patches for a guitar processor. There are two foot driven pedals thatpivot so you can rock the pedal back and forth.On the underside of the pedal, there is a small 3/8" wide and 4" long strip of a flexible plastic with horizontal lines every 2mm or so.The strip passes through a Sharp GP1A71R photointerrupter., Datasheet is here:http://pdf.datasheetcatalog.com/datasheet/Sharp/mXuzuuu.pdfThis sends info to the main processor so you can adjust a parameter of one of the guitar patches in real time...For example, if you set it to control the overall volume of the output signal, rocking all the way back gives you 0 outputand all the way forward 100% output,Problem is that the clear plastic strip with the horizontal black lines has damage as it did not pass through thegap in the GP1A71R cleanly....Any thoughts on how to find a replacement?? Digikey once sold the GP1A71R, but now obsoleteThanksTim

author: alsetalokin4017
author_rank: Super Contributor
timestamp: June 23, 2015, 04:52:55 am
content: Hmmm... I checked the USDigital site for linear encoder strips, but the coarsest they list is 120 lines per inch and they are pricey, like over 20 dollars for a 4 inch strip.Have you considered making your own? Lay out the pattern in a graphics program, then laser-print it to overhead-transparency film.

author: Mr.B
author_rank: Unknown
timestamp: June 23, 2015, 04:53:15 am
content: The datasheet says: GP1A71R Disk slit pitch :0.7mmI don't know if it would work, but you may be able to rip one out of an old inkjet printer.IIRC they are used for head positioning and run the full width of the printer.Was a few years ago though. I don't know if the very modern ones use that method.

author: alsetalokin4017
author_rank: Super Contributor
timestamp: June 23, 2015, 05:05:52 am
content: Quote from: Mr.B on June 23, 2015, 04:53:15 amIn this application, it sounds like the encoder is just counting lines as the pedal travels. So whatever the OEM setup is for the encoder and _disk_, in this application one wants to have the same number and thickness of lines on the replacement linear strip as on the original, so that pedal travel distance = line count as before.Really, it doesn't sound too difficult simply to make one with the required line count and spacing. I don't have any idea how the strip is mounted mechanically though.

author: Mr.B
author_rank: Unknown
timestamp: June 23, 2015, 07:07:31 am
content: Quote from: alsetalokin4017 on June 23, 2015, 05:05:52 amAppreciate this is a linear application.Thats why I suggested investigating the inkjet printer head measurement strips.They would probably be a bit finer than 0.7mm.Your idea of printing one is probably better.

author: amyk
author_rank: Super Contributor
timestamp: June 23, 2015, 01:03:12 pm
content: The inkjet linear encoder strips are far higher resolution than "horizontal lines every 2mm or so" - they start at 150lpi (roughly 170um pitch) and go up from there. Yours is low enough resolution that it should be quite easy to print one on transparency.