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If I got an LCD, and I didn't know anything about it, and there were no markings on the pins, how would I go about interfacing with it? For example, I got this small (around 2.5") colour display out of an old printer, I tried everything I could, looking up a datasheet, asking on forums, but I was unable to get it to work. What is a general process I could use? Is there like, a few common interfaces I could use?

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    \$\begingroup\$ First step: Count the number of pins. Second step: Observe the pins: Are they all the same size? Are they grouped in any way? Third step: Do the total number of pins or the number of pins in a group correspond with any protocols you can find? \$\endgroup\$ – Dampmaskin Jan 18 '18 at 9:20
  • \$\begingroup\$ Okay, thanks for the advice, I don't have the LCD with me right now, but I will try it later. \$\endgroup\$ – skillz21 Jan 18 '18 at 9:21
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    \$\begingroup\$ Very often these displays are custom designs so only the manufacturer of the display and company which made the printer know how to control this LCD. I expect that quite a lot of reverse engineering would need to go into this before you can use such a display in a meaningful way. If you really need a display for some project then it is often much less work to use a readily available display (from ebay for example) which also has software libraries (for Arduino or Rpi) to control it. \$\endgroup\$ – Bimpelrekkie Jan 18 '18 at 9:27
  • \$\begingroup\$ Your best option is to buy a new one with all the data necessary to make it work - trying to reverse engineer it is probably a fruitless exercise... \$\endgroup\$ – Solar Mike Jan 18 '18 at 9:43
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Your best shot is to hook up a signal analyzer on the LCD interface while you still have the working device it comes from. Then you can look at the captured signals and try to identify which protocol it is, what the init sequence looks like and what are typical displaying commands. If all you have is the LCD, there's noting you can analyze, only guess.

Another creative approach I can think of is to take a few pictures of your LCD and p̵o̵s̵t̵ ̵t̵h̵e̵m̵ ̵h̵e̵r̵e̵ use reverse image search. If your LCD is widely used, you will usually find out its model name. If not, I wouldn't even bother, since you can get a known LCD for as little as $2 from e-bay or similar.

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  • \$\begingroup\$ $2??? Do you mean the 16x2 ones? I seriously doubt you could get a graphical LCD for that cheap. \$\endgroup\$ – skillz21 Jan 19 '18 at 3:46
  • \$\begingroup\$ @skillz21 I'm not that familiar with US shops, but here's a graphical LCD for €1.82 including shipping to where I live. \$\endgroup\$ – Dmitry Grigoryev Jan 19 '18 at 8:20

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