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Topic: 7 inch led touchscreen (Read 3691 times) previous topic - next topic

E-CarNut

Has anyone set up a 7 inch touchscreen with an Arduino?  I notice that most of the touchscreens are not very big 2.8 inch or 3.2 inch. What is the reason screens are so small?  I am wanting to set up a http://www.ebay.com/itm/7-Touch-Panel-SSD1963-TFT-LCD-Module-STM32-Dev-Board-/200641684729?pt=BI_Electrical_Equipment_Tools&hash=item2eb72d24f9 panel.  The item has a ssd1963 chip just like the smaller displays. Any starter advice.

Msquare

I'd hazard a guess that 7" is more expensive as the main reason others use smaller displays - or the project has a size limit.

If the chip is the same, there should be no reason why more/fewer inches make any difference. Have you looked at the pixel count? The Arduino has to generate the pixels somehow, and it requiures some trickery with handling/expanding simple shapes to manage that with the RMA in the Arduino. If the 7" has many more pixels...

winner10920

4dsystems makes a 4 inch screen I believe that's very compatible with the arduino, main reason I don't have it is the 300$ price tag
if you get that 7" working that'd be pretty sweet, probably not useful for much tho since I imagine the time it takes for the arduino to refresh a page would be quite slow

E-CarNut

I was also afraid of the possibility of a slower refresh rate.  When programming you can refresh certain block or blocks  and not refresh the whole screen in order to speed up the refresh rates.  But that gets cumbersome trying to figure out what blocks to refresh.  It also eats up lots of memory.

winner10920

I used that technique on a 2.8 in tft screen, simply always having a black background and drawing black a line behind the new drawing, and even still it wasn't very fast, also my loop did many things so it would slow down regularly, and to stop those processes while drawing would be silly

MichaelMeissner

I would imagine that it would be either impossible or very complicated with reduced functionality on an Arduino.  The screen you mention is 800x480 pixels, which is 384,000 bytes using 1 byte for the colors (375k).  Using 1 byte will give you 256 possible colors.  A more common way to represent the image is to use 3 bytes (1 byte for each of the 3 primary colors) which is 1,152,000 bytes (1.1m).  Given the Mega only has 8k of SRAM and 256k of flash memory (the Uno has 2k/32k, the Leonardo 2.5k/32k), there is no way to even hold the entire image in memory to be able to write it out 30 times a second.  If you had just a few images you were using, in theory it might be possible to store them on a SD card and rapidly copy them from the card to the display.

E-CarNut

With over 375k bytes for just the screen size it sounds like an impossibility.  However lots of things seem impossible until tried.  If I was to use a sd card it wouldn't be for pictures it would be for bar graph functions and the such.  It sounds like the arduino would work with a 7 inch screen if the onboard chip had larger SRAM.  Thanks for the facts Michael .

winner10920

Yeah the screens processor can help alot, that's what I like about the 4dsystems one, its basically got its own processor that you can make complex commands on and then have the arduino trigger those and save the arduinos memory for something else

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