ADC.read() returns wrong value

[dengber]

BBB has 12‐bit ADCs (2^12 = 4,096), meaning a value between 0 and 2^12 − 1 (0 to 4,095), read() should return the raw value divided by 4095, not by 1800.

[pdp7]

4.1.15-bone18

read_raw() value:
2782.0
read() value:
0.713308930397
voltage value:
1.28395607471

4.1.16-ti-rt-r44

root@beaglebone:~# python ./adc_test.py 
read_raw() value:
2773.0
read() value:
0.720390737057
voltage value:
1.2967033267

Test program adc_test.py

import Adafruit_BBIO.ADC as ADC
ADC.setup()

#read_raw returns non-normalized value 
value = ADC.read_raw("P9_40")
print "read_raw() value:"
print value

#read returns values 0-1.0 
value = ADC.read("P9_40")
print "read() value:"
print value

print "voltage value:"
voltage = value * 1.8 #1.8V
print voltage

[pdp7]

Thanks @dengber

I've realized that the older 3.81.13 kernel produces ADC raw value of 0 to 1800, so I'm going to push a commit that chooses the right scaling based on kernel version.

[pdp7]

Test OK for all kernels after 4371949

3.8.13-bone80

root@beaglebone:~# python ./test_adc.py
read_raw() value:
1694.0
read() value:
0.94055557251
voltage value:
1.69300003052

4.1.16-ti-rt-r44

root@beaglebone:~# python ./adc_test.py
read_raw() value:
3849.0
read() value:
0.939682543278
voltage value:
1.6914285779

4.1.15-bone18

root@beaglebone:~# python ./test_adc.py
read_raw() value:
3848.0
read() value:
0.941636145115
voltage value:
1.69494506121

4.4.27-bone14

root@beaglebone:~# python ./test_adc.py
read_raw() value:
3849.0
read() value:
0.938949942589
voltage value:
1.69010989666

Test program adc_test.py

import Adafruit_BBIO.ADC as ADC
ADC.setup()

#read_raw returns non-normalized value 
value = ADC.read_raw("P9_40")
print "read_raw() value:"
print value

#read returns values 0-1.0 
value = ADC.read("P9_40")
print "read() value:"
print value

print "voltage value:"
voltage = value * 1.8 #1.8V
print voltage