EBC Exercise 10a Analog In

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thumb‎ Embedded Linux Class by Mark A. Yoder

Analog in

3.8 Kernel

This page is for the Bone (Black or White) running the 3.8 Kernel. See EBC_Exercise_10_Flashing_an_LED_-_xM_WhiteBone for the White Bone or xM running 3.2.

(This is based on BeagleBone Black Analog Input.)

The bone has eight Analog Inputs. Several are exposed on P9. They are labeled AIN in table 11 below. How many do you find?


The AIN pins are sampled at 12 bits and 100k samples per second. The input voltage is between 0 and 1.8V. Fortunately, both voltages are available on P9.

The photo below shows a small potentiometer wired to the bone. One end goes to the analog ground (pin 34), the other analog 1.8V (pin 32). The wiper is attached to AIN5 which is pin 36.

Bone gpio.JPG BoneGPIO.png

You interact with the analog in much like the gpio, but it appears in a different. We have to run a command before the AIN interface appears. Just run them now, later we'll explain what you did. Note: On the debian 8.5 image, you must be logged in as root in order to use the '>' modifier. use 'su root' to do this. (otherwise you will get a permissions error)

beagle$ cd /sys/devices/platform/bone_capemgr
beagle$ echo BB-ADC > slots

You can now access the analog interface, but where do they appear. Try using the find command.

beagle$ find /sys -name "in_voltage*_raw"

Ian's Notes: If find /sys -name "*AIN" fails, try find /sys -name "*AIN*"

You paths may be slightly different. Now explore.

beagle$ cd /sys/bus/iio/devices/iio:device0
beagle$ ls -F
buffer		 in_voltage1_raw  in_voltage4_raw  name     scan_elements
dev		 in_voltage2_raw  in_voltage5_raw  of_node  subsystem
in_voltage0_raw  in_voltage3_raw  in_voltage6_raw  power    uevent

There are the various analog inputs, in_voltage6_raw corresponds with AIN6

beagle$ cat in_voltage6_raw

Change the pot and rerun cat. What's the min and max value you get? Is it 12 bits?


Rewrite the scripts from before to read an AIN pin and continuously display it's value.

thumb‎ Embedded Linux Class by Mark A. Yoder