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Without going into boring details, I need to get a touchscreen input into a Raspberry Pi which will be "faked" by a microcontroller - so the micro is reading some input and translating it to a touch coordinate and passing it to the Pi.

This means I want to choose a well-supported and hopefully not too complicated touchscreen device to emulate in the micro so that I don't have to modify the standard Raspberry Pi OS with extra drivers etc. any more than is absolutely necessary.

It doesn't need anything more than single-touch capability if that helps, but it must be I2C based.

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    Pretty sure touchscreens are standardized for USB (ie., generally made to fulfill a generic public protocol). So chances are all you have to do is make something that also fulfills it (no need for reverse engineering).
    – goldilocks
    Feb 3, 2021 at 15:17
  • It's not USB though, it's through I2C interface.
    – John U
    Feb 3, 2021 at 16:25
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    Dunno if there is a generic standard for that. There are a bunch of drivers for them in the kernel source though, grep -i i2c [src]/drivers/input/touchscreen should get them. Take your pick...
    – goldilocks
    Feb 3, 2021 at 17:53
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    What I2C based touch screens have you found so far @JohnU? Feb 3, 2021 at 22:29

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There are many touschscreens for the Pi that use an I2C interface.

Pimoroni's HyperPixel uses a FocalTech FT6236. Datasheet for the controller.

AdaFruit's PiTFT 2.8" uses a FocalTech FT6206.

Both of these are capactive multi-touch, and use drivers that are already in the Raspberry Pi OS. Check out the DTS file to see which driver is used, how it is configured etc.

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