beaglebone ADC AIN0 AIN2 AIN3 cannot be used?

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1

I used beaglebone white to implement ADC.
However, when I use a signal generator and oscilloscope to see the input wave,
There is always 1.8V in AIN0 , and always 0V in AIN2 and AIN3, but it is correct when I use AIN1 4 5 6,
Could anyone help me？

does that adc internal resistance cause it？ Or how should I modify ADC-related files to get correct signal？

2

This seems to be a problem with the ADC configuration. You could run one of the libpruio examples io_input or oszi to check the hardware or the example analyse to check the configuration. (The pins may be configured for touch screen?)

To get more detailed information you should describe the steps you perform to receive the ADC values. (Do you use sysfs, mmap, a library, … ?)

3

I used beaglebone white to implement ADC.
However, when I use a signal generator and oscilloscope to see the input wave,
There is always 1.8V in AIN0 , and always 0V in AIN2 and AIN3, but it is correct when I use AIN1 4 5 6,
Could anyone help me？

Disable the touchscreen driver.

Regards,
John

4

thanks, TJF, I will try John’s method first, it seems easier.

5

Hi, John.
Could you teach me how to disable touchscreen driver？
should I delete the “cape-bone-lcd3-00A0.dtbo” under /lib/firmware ?
or should I modify “am335x-bone.dtb” under /boot ？

6

Hi, John.
Could you teach me how to disable touchscreen driver？
should I delete the “cape-bone-lcd3-00A0.dtbo” under /lib/firmware ?
or should I modify “am335x-bone.dtb” under /boot ？

You need to disable the touchscreen in the kernel .config. Easiest way is to do the following:

In the Kernel folder:
make xconfig

Under Device Drivers/Staging drivers

Unselect "TI Touchscreen Interface”

Save and rebuild kernel

Alternatively, edit the .config file:

Search for CONFIG_TOUCHSCREEN_TI_AM335X_TSC=y

Change to

CONFIG_TOUCHSCREEN_TI_AM335X_TSC is not set

Save and rebuild kernel.

http://eewiki.net/display/linuxonarm/BeagleBone+Black

Regards,
John

7

John:
It works fine on my beaglebone, thanks.
Also I can see that there is an small offset (~10mV) in different ADC input, but it doesn’t matter because I can handle it by using a voltage divider.

john3909於 2014年6月11日星期三UTC+8下午1時42分35秒寫道：