zwabbit

Second opinion on whether this touchscreen shield will fry a papilio

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So it might just be my bad luke but one of the shields I was working to see if I could get working connected to a papilio is the adafruit 2.8" LCD shield. The schematic is located here: https://raw.github.c...aster/schem.png

The thing that caught my attention was their marking the I/O pins as 5V, both read and right. Does that actually mean this thing will output 5V or will I need to take a volt meter to the thing to be sure? Cause if it does output 5V, I presumably need to wrap up that voltage buffer board to avoid frying the papilio I have.

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If you look at the schematic carefully and also the datasheet for the ILI9325 you will see that the ILI9325 is a 3.3V device. The schematic for the shield shows that power to the LCD goes from 5V via the ADP122 LDO regulator which drops the 5V down to 3.3V. I don't see any purpose for the ACT245 buffers, the way they are connected to 3.3V power, other than they are being used as 5V tolerant voltage level translators to bring down the input signals down to the 3.3V required by the LCD. Because the ACT245 buffers are powered by 3.3V they cannot output any voltage higher than that, so they can be directly connected to the FPGA.

So long story short, if you supply the shield with 5V it can still be safely connected to teh FPGA. You will not be able to use the touch functionality of the LCD, pins X+/- Y+/- as they require analog to digital conversion.

You should be also able to connect the SD/MMC slot to the FPGA as that is also powered from 3.3V, basically anything labeled VCC is powered by the ADP122 output which is 3.3V

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zwabbit,

Take a look at this blog post:

http://www.gadgetfactory.net/2011/10/experimentation-with-tft-touchscreens/

I used the adafruit tft library to drive a $10 ILI9325 display that was purchased from ebay. Those displays are designed to run at 3.3V originally, and Alex might be on to something that the level translators are just providing 5V tolerance but really outputting 3.3V. Do a test with your multimeter to be sure.

Keep us posted how it goes, I have some experience with those displays so I can help out.

Jack.

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