beagle bone black read ain7

Ahn

Intellectual 1000 points

Hi,

I want read the ain7 value in BBB.

But following command's result is empty.

# find /sys/ -name "ain*"

How to read?

over 9 years ago

0 Biser Gatchev-XID over 9 years ago

TI__Guru**** 393215 points

Hi,

What Linux version are you using?

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

Intellectual 1000 points

I'm using the linux-3.14.26-g2489c02

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

TI__Guru**** 393215 points

See this wiki for ADC configuration and usage: processors.wiki.ti.com/.../Linux_Core_ADC_User's_Guide

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

Intellectual 1000 points

Here is my test result.

##############################################################
# ls -al /sys/bus/iio/devices/iio\:device0/
drwxr-xr-x 5 root root 0 Jan 1 00:00 .
drwxr-xr-x 4 root root 0 Jan 1 00:00 ..
drwxr-xr-x 2 root root 0 Jan 1 00:00 buffer
-r--r--r-- 1 root root 4096 Jan 1 00:00 dev
-rw-r--r-- 1 root root 4096 Jan 1 00:00 in_voltage4_raw
-rw-r--r-- 1 root root 4096 Jan 1 00:00 in_voltage5_raw
-rw-r--r-- 1 root root 4096 Jan 1 00:00 in_voltage6_raw
-rw-r--r-- 1 root root 4096 Jan 1 00:00 in_voltage7_raw
-r--r--r-- 1 root root 4096 Jan 1 00:00 name
drwxr-xr-x 2 root root 0 Jan 1 00:00 power
drwxr-xr-x 2 root root 0 Jan 1 00:00 scan_elements
lrwxrwxrwx 1 root root 0 Jan 1 00:00 subsystem -> ../../../../../bus/iio
-rw-r--r-- 1 root root 4096 Jan 1 00:00 uevent

# cat /sys/bus/iio/devices/iio\:device0/in_voltage7_raw
3871
##############################################################

Is it correct to read in_voltage7_raw?

3871 what that means? 3.871v?

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

TI__Guru**** 393215 points

Ahn said:
3871 what that means? 3.871v?

ADC input voltages cannot exceed VREFP, which is 1.8V in BBB. This is the binary value that is read from AIN7 in decimal representation. This would correspond to 1.8V * (3871 / 4096) = 1.7V

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

Intellectual 1000 points

How to determined VREFP?

Is VREF of am335x always 1.8V?

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

TI__Guru**** 393215 points

Ahn said:
How to determined VREFP?

This is the ADC reference voltage. It's either provided on processor pins or taken from internal source. Read the AM335X documentation for details.

Ahn said:
Is VREF of am335x always 1.8V?

Not necessarily, but if 1.8V positive reference and GND negative reference is used you will get best performance from the ADC.

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beagle bone black read ain7