A more complete listing

***PI_Controller.py***
#!/usr/bin/python
"""
PI Controller for BeagleBone Black
"""
__author__ = "Joe Moquin"
__copyright__ = "Copyright 2015, Smart Green Power Node"
__credits__="""
                Brett Beauregard:
                http://brettbeauregard.com/blog/2011/04/improving-the-beginners-pid-introduction/
            """
__email__ = "sjmoquin@gmail.com"
__maintainer__ = "Joe Moquin"
__status__ = "Alpha"
__version__ = "0.1"

from time import clock
import Adafruit_BBIO.ADC as ADC
#import Adafruit_BBIO.PWM as PWM
import signal

class PI_Controller:
    """
    Handles storage and calculation of PWM output from ADC input.
    Derivative values removed.
    """
    def __init__(self):
        self.ADC_input = 0.0
        self.errSum = 0.0
        self.kp = 0.0
        self.ki = 0.0

        self.lastTime = 0
        self.lastErr = 0.0
        self.PWM_output = 0.0
        self.sample_time = 1000
        self.setpoint = 0.0

    def Compute(self, ADC_input):
        #For reporting
        self.ADC_input = ADC_input
        #How long since we last calculated, in miliseconds
        now = int(1000*clock())

        dt = now - self.lastTime
        if dt >= self.sample_time
            """
            #boost_voltage = Black_Magic * ADC_input

            #Compute all the working error variables for PI
            error = self.setpoint - boost_voltage
            self.errSum = self.errSum + error


            #Compute PID Output
            boost_feedback_voltage = self.kp * error + self.ki * self.errSum
            PWM_output = Devil_Magic * boost_feedback_voltage

            #For reporting
            self.PWM_output = PWM_output
            """
            PWM_output = 90.0
            self.PWM_output
            #Remember some variables for next time
            #self.lastErr = error
            self.lastTime = now

            return PWM_output
        else:
            return self.PWM_output

    def print_handler(self, signum, frame):
        """
        Prints ADC input and PWM output upon USR1 signal from environment.

        In Terminal, type:
        ps -C python

        You'll get something like
        debian@beaglebone:~$ ps -C python
          PID TTY          TIME CMD
          2276 pts/0    00:04:16 python
        in reply.

        Type in the following, using the PID from the ps command:
        sudo kill -s USR1 2276

        In the PI_Controller.py's terminal, the following will print.
        """
        print "ADC_input:\t{}".format(self.ADC_input)
        print "boost_PWM:\t{}".format(self.PWM_output)

    def set_kp(self, kp):
       self.kp = kp

    def set_ki(self, ki):
        self.ki = ki * self.sample_time/1000

    def set_setpoint(self, setpoint):
        self.setpoint = setpoint




if __name__ == "__main__":
    ADC.setup()
    #PWM.start(channel, duty, freq=2000, polarity=0)
    #PWM.start("P9_14", 100, 10000, 0)
    pi = PI_Controller()
    signal.signal(signal.SIGUSR1, pi.print_handler)

    while True:
        #Pesky ADC read gives faulty values for first few reads.
        #So, just read a few times, saving the last read.
        ADC_input = 0.5
        for __ in range(5):
            ADC_input = ADC.read("P9_40")

        boost_PWM = pi.Compute(ADC_input)
        #PWM.set_frequency(boost_PWM)



***Python Output***

debian@beaglebone:~/UCB$ sudo python PI_Controller.py
Traceback (most recent call last):
  File "PI_Controller.py", line 101, in <module>
    ADC.setup()
RuntimeError: Unable to setup ADC system. Possible causes are:
  - A cape with a conflicting pin mapping is loaded
  - A device tree object is loaded that uses the same name for a fragment: helper

***BASH Output***
root@beaglebone:/lib/firmware# echo BB-UART1 > /sys/devices/platform/bone_capemgr/slots
bash: echo: write error: Invalid argument
root@beaglebone:/lib/firmware# echo BB-UART1 >> /sys/devices/platform/bone_capemgr/slots
bash: echo: write error: Invalid argument
root@beaglebone:/lib/firmware# echo ADAFRUIT-SPI0-00A0 >> /sys/devices/platform/bone_capemgr/slots
bash: echo: write error: No such file or directory