Difference between revisions of "EBC Exercise 10a Analog In"

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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.
 
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$ '''SLOTS=/sys/devices/bone_capemgr.*/slots'''
+
  beagle$ '''cd /sys/devices/platform/bone_capemgr'''
beagle$ '''PINS=/sys/kernel/debug/pinctrl/44e10800.pinmux/pins'''
+
  beagle$ '''echo BB-ADC > slots'''
  beagle$ '''echo cape-bone-iio > $SLOTS'''
+
  
 
You can now access the analog interface, but where do they appear.  Try using the '''find''' command.
 
You can now access the analog interface, but where do they appear.  Try using the '''find''' command.
  
  beagle$ '''find /sys -name "*AIN"'''
+
  beagle$ '''find /sys -name "in_voltage*_raw"'''
  ./devices/ocp.2/helper.14/AIN0
+
 
  ./devices/ocp.2/helper.14/AIN1
+
  /sys/devices/platform/ocp/44e0d000.tscadc/TI-am335x-adc/iio:device0/in_voltage0_raw
  ./devices/ocp.2/helper.14/AIN2
+
  /sys/devices/platform/ocp/44e0d000.tscadc/TI-am335x-adc/iio:device0/in_voltage1_raw
  ./devices/ocp.2/helper.14/AIN3
+
  /sys/devices/platform/ocp/44e0d000.tscadc/TI-am335x-adc/iio:device0/in_voltage2_raw
  ./devices/ocp.2/helper.14/AIN4
+
  /sys/devices/platform/ocp/44e0d000.tscadc/TI-am335x-adc/iio:device0/in_voltage3_raw
  ./devices/ocp.2/helper.14/AIN5
+
  /sys/devices/platform/ocp/44e0d000.tscadc/TI-am335x-adc/iio:device0/in_voltage4_raw
  ./devices/ocp.2/helper.14/AIN6
+
  /sys/devices/platform/ocp/44e0d000.tscadc/TI-am335x-adc/iio:device0/in_voltage5_raw
./devices/ocp.2/helper.14/AIN7
+
  /sys/devices/platform/ocp/44e0d000.tscadc/TI-am335x-adc/iio:device0/in_voltage6_raw
 +
 
 +
 
 +
Ian's Notes: If find /sys -name "*AIN" fails, try find /sys -name "*AIN*"
  
 
You paths may be slightly different. Now explore.
 
You paths may be slightly different. Now explore.
  
  beagle$ '''cd /sys/devices/ocp.2/helper.14'''
+
  beagle$ '''cd /sys/bus/iio/devices/iio:device0'''
 
  beagle$ '''ls -F'''
 
  beagle$ '''ls -F'''
AIN0  AIN2  AIN4  AIN6  driver@  power/      uevent
 
AIN1  AIN3  AIN5  AIN7  modalias  subsystem@
 
  
There are the various analog inputs, but watch out.  This interface starts numbering at '''1''' and Table 11 starts at '''0''', so to read AIN5 you need to look at '''AIN6'''!
+
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 AIN6'''
+
  beagle$ '''cat in_voltage6_raw'''
 
  1185
 
  1185
  

Latest revision as of 13:32, 4 September 2016

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?

HeaderP9.jpg

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"
/sys/devices/platform/ocp/44e0d000.tscadc/TI-am335x-adc/iio:device0/in_voltage0_raw
/sys/devices/platform/ocp/44e0d000.tscadc/TI-am335x-adc/iio:device0/in_voltage1_raw
/sys/devices/platform/ocp/44e0d000.tscadc/TI-am335x-adc/iio:device0/in_voltage2_raw
/sys/devices/platform/ocp/44e0d000.tscadc/TI-am335x-adc/iio:device0/in_voltage3_raw
/sys/devices/platform/ocp/44e0d000.tscadc/TI-am335x-adc/iio:device0/in_voltage4_raw
/sys/devices/platform/ocp/44e0d000.tscadc/TI-am335x-adc/iio:device0/in_voltage5_raw
/sys/devices/platform/ocp/44e0d000.tscadc/TI-am335x-adc/iio:device0/in_voltage6_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
1185

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

Challenge

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




thumb‎ Embedded Linux Class by Mark A. Yoder