Hi,
I'm testing an AD7746 eval board using a Diolan DLN-2 adapter. I wrote
some basic notes about the installation an instanciation process for my
own use. But then I thought it could be useful for someone else. So
maybe I could put this in the kernel newbies page under the IIO section?
If you think is worth it, I would be glad to add it to the wiki page.
Best regards,
Gaston
Notes:
The setup
=========
AD7746-EVAL BOARD --> Diolan DLN-2 Adapter --> Thinkpad T430
The connection between the AD7746 eval board and adapter is as detailed
in [2] I2C Interface Configuration Options, External connection (pag 4).
The connection between Diolan DLN-2 and the T430 is USB straighforward.
Drivers
=======
Both in mainline kernel:
- Diolan DLN-2 driver: I2C_DLN2 (prompt Diolan DLN-2 USB I2C adapter)
Loc: drivers/i2c/busses/
- AD7746: AD7746
Loc: drivers/staging/iio/cdc/
Bus of interest
===============
$ sudo i2cdetect -l
We get something like:
...
i2c-10 i2c dln2-i2c-1-1.2:1.0-0 I2C adapter
...
So our bus is the number 10.
Getting the address
===================
$ sudo i2cdetect -y -r 10
We get something like:
0 1 2 3 4 5 6 7 8 9 a b c d e f
00: -- -- -- -- -- -- -- -- -- -- -- -- --
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
40: -- -- -- -- -- -- -- -- 48 -- -- -- -- -- -- --
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
70: -- -- -- -- -- -- -- --
3. Device instantiation:
# echo add7746 0x48 > /sys/bus/i2c/devices/i2c-10/new_device
We must see something like:
$ cd /sys/bus/i2c/devices/i2c-10/10-0048/
$ ls
driver iio:device0 modalias name power subsystem uevent
$ cd iio:device0
$ ls
dev in_capacitance-capacitance_calibbias
in_capacitance0_calibbias_calibration
in_capacitance-capacitance_sampling_frequency
in_capacitance0_calibscale in_capacitance-capacitance_scale
in_capacitance0_calibscale_calibration in_capacitance_sampling_frequency
in_capacitance0-capacitance2_calibscale
in_capacitance_sampling_frequency_available
in_capacitance0-capacitance2_offset in_capacitance_scale
in_capacitance0-capacitance2_raw in_temp0_input
in_capacitance0_offset in_temp1_input
in_capacitance0_raw in_voltage0_calibscale_calibration
in_capacitance1_calibbias_calibration in_voltage0_raw
in_capacitance1_calibscale in_voltage1_supply_raw
in_capacitance1_calibscale_calibration in_voltage_sampling_frequency
in_capacitance1-capacitance3_calibscale in_voltage_sampling_frequency_available
in_capacitance1-capacitance3_offset in_voltage_scale
in_capacitance1-capacitance3_raw name
in_capacitance1_offset power
in_capacitance1_raw subsystem
in_capacitance_calibbias uevent
Checking the permits:
$ ll
-r--r--r-- 1 root root 4096 mar 31 09:57 dev
--w------- 1 root root 4096 mar 31 09:57 in_capacitance0_calibbias_calibration
-rw-r--r-- 1 root root 4096 mar 31 09:57 in_capacitance0_calibscale
--w------- 1 root root 4096 mar 31 09:57 in_capacitance0_calibscale_calibration
-rw-r--r-- 1 root root 4096 mar 31 09:57 in_capacitance0-capacitance2_calibscale
-rw-r--r-- 1 root root 4096 mar 31 09:57 in_capacitance0-capacitance2_offset
-rw-r--r-- 1 root root 4096 mar 31 09:57 in_capacitance0-capacitance2_raw
-rw-r--r-- 1 root root 4096 mar 31 09:57 in_capacitance0_offset
-rw-r--r-- 1 root root 4096 mar 31 09:57 in_capacitance0_raw
--w------- 1 root root 4096 mar 31 09:57 in_capacitance1_calibbias_calibration
-rw-r--r-- 1 root root 4096 mar 31 09:57 in_capacitance1_calibscale
--w------- 1 root root 4096 mar 31 09:57 in_capacitance1_calibscale_calibration
-rw-r--r-- 1 root root 4096 mar 31 09:57 in_capacitance1-capacitance3_calibscale
-rw-r--r-- 1 root root 4096 mar 31 09:57 in_capacitance1-capacitance3_offset
-rw-r--r-- 1 root root 4096 mar 31 09:57 in_capacitance1-capacitance3_raw
-rw-r--r-- 1 root root 4096 mar 31 09:57 in_capacitance1_offset
-rw-r--r-- 1 root root 4096 mar 31 09:57 in_capacitance1_raw
-rw-r--r-- 1 root root 4096 mar 31 09:57 in_capacitance_calibbias
-rw-r--r-- 1 root root 4096 mar 31 09:57 in_capacitance-capacitance_calibbias
-rw-r--r-- 1 root root 4096 mar 31 09:57
in_capacitance-capacitance_sampling_frequency
-rw-r--r-- 1 root root 4096 mar 31 09:57 in_capacitance-capacitance_scale
-rw-r--r-- 1 root root 4096 mar 31 09:57 in_capacitance_sampling_frequency
-r--r--r-- 1 root root 4096 mar 31 09:57
in_capacitance_sampling_frequency_available
-rw-r--r-- 1 root root 4096 mar 31 09:57 in_capacitance_scale
-rw-r--r-- 1 root root 4096 mar 31 09:57 in_temp0_input
-rw-r--r-- 1 root root 4096 mar 31 09:57 in_temp1_input
--w------- 1 root root 4096 mar 31 09:57 in_voltage0_calibscale_calibration
-rw-r--r-- 1 root root 4096 mar 31 09:57 in_voltage0_raw
-rw-r--r-- 1 root root 4096 mar 31 09:57 in_voltage1_supply_raw
-rw-r--r-- 1 root root 4096 mar 31 09:57 in_voltage_sampling_frequency
-r--r--r-- 1 root root 4096 mar 31 09:57 in_voltage_sampling_frequency_available
-rw-r--r-- 1 root root 4096 mar 31 09:57 in_voltage_scale
-r--r--r-- 1 root root 4096 mar 31 09:57 name
drwxr-xr-x 2 root root 0 mar 31 09:57 power
lrwxrwxrwx 1 root root 0 mar 31 09:57 subsystem ->
../../../../../../../../../../../bus/iio
-rw-r--r-- 1 root root 4096 mar 31 09:57 uevent
4. Capacitance
According to [2], the capacitive length sensor is connected to CIN2+ and
CIN2-. In the driver, the values are mapped to capacitance0.
Raw values vs sensor length:
Note: (+) values means the sensor was moved to the left, (-) values
means the sensor was moved to the right. I.e. +1 cm means the rule was
moved 1 to the left, while -1 means the rule was moved 1 cm to the
right.
Note2: note the raw value for -10 is 8224733, while +10 is -8224726, the
difference is because when the rule is moved 10 cm to the left, the is
still 2 o 3 cm of dielectric between the plates. The design is obviously
thought to move the rule to the right.
Length (cm) | Raw Value Cap0
------------------------------
-10 -8224733
-9 -8224730
-8 -8224728
-7 -8224725
-6 -8224724
-5 -8224722
-4 -8224720
-3 -8224718
-2 -8224716
-1 -8224714
+0 -8224711
+1 -8224711
+2 -8224711
+3 -8224711
+4 -8224713
+5 -8224715
+6 -8224717
+7 -8224719
+8 -8224721
+9 -8224723
+10 -8224726
References
==========
[1]
http://www.analog.com/media/en/technical-documentation/data-sheets/AD7745_7746.pdf
[2]
http://www.analog.com/media/en/technical-documentation/evaluation-documentation/EVAL-AD7746EB.PDF
[3] https://i2c.wiki.kernel.org/index.php/Main_Page
[4]
https://kernelsense.wordpress.com/2016/01/22/achievement-unlocked-first-iio-driver/
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