AM335x Linux ADC Measurement on EVM

Hiroyasu Tazawa1

Guru 12350 points

Hi,Everyone

I need your help.
We use AM335x EVM and evaluate ADC.

I use ADC driver of Linux ProcesserSDK 1.0 and 2.0. like this.

○AM335x ADC Driver's Guide
How to set it up
processors.wiki.ti.com/.../AM335x_ADC_Driver's_Guide

We use TSC_AIN5 of J8 on Daughterboard.
but We got noize.I do not why.

LinuxADC.xlsx

Could you give me advice ?

Best Regards
Hiroyasu

over 9 years ago

0 Biser Gatchev-XID over 9 years ago

TI__Guru**** 393215 points

Hi,

The wiki guide you use is for old Linux versions. The current ADC wiki portal is here: processors.wiki.ti.com/.../Processor_SDK_Linux_ADC

0 Hiroyasu Tazawa1 over 9 years ago in reply to Biser Gatchev-XID

Guru 12350 points

Hi, Biser

I think it is not old version.
Because I watch　”AM335x ADC and Touchscreen Linux Driver Users Guide” in URL you send.
Can you check it ?

Best Regards
Hiroyasu

0 Biser Gatchev-XID over 9 years ago in reply to Hiroyasu Tazawa1

TI__Guru**** 393215 points

This is the wiki guide for current kernels: processors.wiki.ti.com/.../Linux_Core_ADC_User's_Guide Perhaps there is a wrong link in the previous wiki page.

0 Hiroyasu Tazawa1 over 9 years ago in reply to Biser Gatchev-XID

Guru 12350 points

Hi, Biser

I watched your link.
I think it is not same link. but it is same shell command I use between old link and new link, isn't it?

===================
How to set it up

Set up the channels in use (you can enable any combination of the channels you want)

root@arago-armv7:~# echo 1 > /sys/bus/iio/devices/iio\:device0/scan_elements/in_voltage0_en
root@arago-armv7:~# echo 1 > /sys/bus/iio/devices/iio\:device0/scan_elements/in_voltage5_en
root@arago-armv7:~# echo 1 > /sys/bus/iio/devices/iio\:device0/scan_elements/in_voltage7_en

Set up the buffer length

root@arago-armv7:~# echo 100 > /sys/bus/iio/devices/iio\:device0/buffer/length

Enable the capture

root@arago-armv7:~# echo 1 > /sys/bus/iio/devices/iio\:device0/buffer/enable

===================

I call same shell command.
I wanna know why it get noize.

Best Regards
Hiroyasu

0 Biser Gatchev-XID over 9 years ago in reply to Hiroyasu Tazawa1

TI__Guru**** 393215 points

I would suggest you do the same test without the signal source, tying the AIN to GND with a resistor. This will let you know if the noise is coupled from outside or from the EVM itself.

0 peaves over 9 years ago in reply to Biser Gatchev-XID

TI__Guru 62945 points

For some reason the noise seamed to disapear as your input voltage approached zero. I think you need to understand why this happened, as it may be key to understanding your issue. I would suggest you connect the input to a low impeadnce divide by 2 voltage divider connected across VREFP and VREFN. This should produce a steady half-scale value.

Regards,
Paul

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AM335x Linux ADC Measurement on EVM