HyperPixel Touchscreen Calibration Issue

[gadgetoid]

@LyyK

I ran the python code above on the raspi but nothing explicitly stood out in a way that I could make sense of. I’ve used similar code as the one above for testing when first getting into reverse engineering as a hobby, only it monitored changes in mouse (the computer kind) position readings instead, little of which is likely to be applicable here except for x and y but I digress.

And that’s half the battle :D Briefly:

The touch screen is driven by a discrete grid of electrodes wired up to an ADC. As such it doesn’t have 800x480 actual points of sensitivity, but rather (IIRC) 13 x 7 lines.

The line row/column intersection that your finger is closest to will read the highest value, and the next closest will have the next highest value and so on. If your finger is exactly between two intersections then they should, in theory, both read the same value. So, to get the position of a finger you find the adjacent intersections that have a highest value, and interpolate between their locations depending on their values.

IE: If you have point A and point B that are reading 75 and 25 (totally arbitrary values you wont see in reality) then you can approximate that the finger is 3 times closer to A than it is to B.

There’s no electrical limit to the number of touches you can track simultaneously on this display, but there are practical ones - sooner or later it becomes impossible to tell the difference between fingers.

I agree with right-click emulation, it’s something I miss from the official display. There is an app to make it work, but it’s a bodge. See: GitHub - pimoroni/raspberry-pi-two-finger-touch: Simple installer and binary for running the twofing application on the official Raspberry Pi 7" touchscreen, to enable two-finger right click

(Note: This doesn’t work well on HyperPixel because it’s native tracking of two-fingers leaves a little to be desired)

@thediveo

Using the Python script and then touching my shiny new HyperPixel I can clearly see that it doesn’t detect anything within a certain region.

As it happens I saw your post late last night and thought I should link you to this code example to confirm. Looks like you’ve taken the initiative though and beat me to it.

It sound like a bug, not a feature. I think you might need a replacement.

@alphanumeric

Slightly off topic, but one of my biggest disappointments with the Pi Foundation touch screen and Raspbian, is the lack of multi touch. It’s 10 point capacitive touch, but only supports single touch out of the box? Not even right click functionality. So I can se why people would want this on what ever display they are using.

Yeah, I’m not sure 100% why there’s a total lack of support for gestures in Pixel, but then I haven’t used many Linux desktops, much less touchscreen-enabled ones so I don’t know what the wider state of support is like.

It’s a shame, because all 10 points of multi-touch are there and supported in my Python-MultiTouch examples to do things like dual-analog onscreen controls and multi-player pong: GitHub - pimoroni/python-multitouch: Multi-touch pure Python driver for the official 7" touchscreen display.