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Beaglebone black adc noise induced from touchscreen LCD

Naseer Nazar
Intellectual 470 points

Hi All,

I have a simple setup, a beaglebone black (version c) with a 4dcape-43T and 4 adc channels. Adc channels are not connected. I am getting noise on BBB adc AIN7 (measuring the BBB 3v3 line).  The noise exists for sdk  1.00.00.00, 02.00.01.07 and 02.00.02.11. Physically removing the LCD the noise on AIN7 drops to 2 LSB and with LCD connected, AIN7 noise goes over 100 LSB.

So I did some hacking. Disconnected the backlight, LCD data lines. Boiled down to LCD PCLK inducing noise on the adc lines. I also noticed the LCD FFC cable has no separate analogue ground (is this common?). Now the touchscreen is kind of working so could someone tell me how the noise was dealt with on the BBB.

best regards

Naseer