Need help writing script for Digital DAQ

Question

Hello,
I am trying to write an aquisition program for digital input coming from a hall sensor.  I will be passing a magnet over a hall sensor on a motor and want to record the number of rotations.  I have pasted together a script based on various websites, but it isn't functioning the way I want.  I would like to be able to collect data points indefinately, or fixed, and then print out the resulting count.  I have attepted to use the ctypes wrapper in Python.  The NI functions remain unchanged though, so if you don't know Python it shouldn't be a problem to read.  I am using a NI PCI-6503. 
NI PCI-6503
NI PCI-6503
NI PCI-6503
The code:
# C:\Program Files\National Instruments\NI-DAQ\Examples\DAQmx ANSI C\Analog In\Measure Voltage\Acq-Int Clk\Acq-IntClk.c
import ctypes
import numpy
nidaq = ctypes.windll.nicaiu # load the DLL
# Setup some typedefs and constants
# to correspond with values in
# C:\Program Files\National Instruments\NI-DAQ\DAQmx ANSI C Dev\include\NIDAQmx.h
# the typedefs
int32 = ctypes.c_long
uInt32 = ctypes.c_ulong
uInt64 = ctypes.c_ulonglong
float64 = ctypes.c_double
TaskHandle = uInt32
# the constants
DAQmx_Val_ChanForAllLines = int32(0)
def CHK(err):
"""a simple error checking routine"""
     if err < 0:
          buf_size = 200
          buf = ctypes.create_string_buffer('\000' * buf_size)
          nidaq.DAQmxGetErrorString(err,ctypes.byref(buf),buf_size)
          raise RuntimeError('nidaq call failed with error %d: %s'%(err,repr(buf.value)))
# initialize variables
taskHandle = TaskHandle(0)
max_num_samples = 1000
# array to gather points
data = numpy.zeros((max_num_samples,),dtype=numpy.float64)
# now, on with the program
CHK(nidaq.DAQmxCreateTask("",ctypes.byref(taskHandle)))
CHK(nidaq.DAQmxCreateDIChan(taskHandle,'Dev1/port1/line1',"", DAQmx_Val_ChanForAllLines))
CHK(nidaq.DAQmxStartTask(taskHandle))
read = int32()
CHK(nidaq.DAQmxReadDigitalU32(taskHandle,int32(-1),float64(1),DAQmx_Val_GroupByChannel,data.ctypes.data,max_num_samples,ctypes.byref(read),None))
print "Acquired %d points"%(read.value)
if taskHandle.value != 0:
     nidaq.DAQmxStopTask(taskHandle)
     nidaq.DAQmxClearTask(taskHandle)
print "End of program, press Enter key to quit"
raw_input()
This script returns "Acquired 1 points" immediately, regardless of how many times the hall sensor has been switched.  
I apologize for the sloppy code, but I understand very little of the underlying principles of these DAQ functions, despite reading their documentation.  Seeing as how the code does not return an error, I am hoping there is just a minor tweak or two that will be farily obvious to someone with more experience.  
Thanks

Answer 1

Hey Daniel,
Most of this script is from http://www.scipy.org/Cookbook/Data_Acquisition_with_NIDAQmx. 
I needed to run the ReadDigitalU32 function in Python loop because my DAQ device did not support timed aquistion and I don't have LabView.  
import numpy
import time
import ctypes
nidaq = ctypes.windll.nicaiu # load the DLL
# Setup some typedefs and constants
# to correspond with values in
# C:\Program Files\National Instruments\NI-DAQ\DAQmx ANSI C Dev\include\NIDAQmx.h
# the typedefs
int32 = ctypes.c_long
uInt32 = ctypes.c_ulong
uInt64 = ctypes.c_ulonglong
float64 = ctypes.c_double
TaskHandle = uInt32
# the constants
DAQmx_Val_Cfg_Default = int32(-1)
DAQmx_Val_Volts = 10348
DAQmx_Val_Rising = 10280
DAQmx_Val_FiniteSamps = 10178
DAQmx_Val_GroupByChannel = 0
DAQmx_Val_ChanForAllLines = int32(0)
# initialize variables
taskHandle = TaskHandle(0)
max_num_samples = 10000
data = numpy.zeros((max_num_samples,),dtype=numpy.float64)
read = uInt32()
bufferSize = uInt32(10000)
def CHK(err):
"""a simple error checking routine"""
     if err < 0:
          buf_size = 200
          buf = ctypes.create_string_buffer('\000' * buf_size)
          nidaq.DAQmxGetErrorString(err,ctypes.byref(buf),buf_size)
          raise RuntimeError('nidaq call failed with error %d: %s'%(err,repr(buf.value)))
# Start up DAQ
CHK(nidaq.DAQmxCreateTask("",ctypes.byref(taskHandle)))
CHK(nidaq.DAQmxCreateDIChan(taskHandle,"Dev?/port?/line?","", DAQmx_Val_ChanForAllLines))
CHK(nidaq.DAQmxStartTask(taskHandle))
#initialize lists and time 1 
t1 = time.time()
times = []
points = []
while True:
     try:
          CHK(nidaq.DAQmxReadDigitalU32(taskHandle,int32(-1),float64(1),
          DAQmx_Val_GroupByChannel,data.ctypes.data,uInt32(2*bufferSize.value)
         ,ctypes.byref(read), None))
          t2 = time.time()
         #data[0] is the position in the numpy array 'data' that holds the value aquired
         #from your device
         points.append(data[0])
         times.append(t2 - t1) 
         t1 = time.time()
         #Choose time interval between data aquisition
         time.sleep(.02)
     except KeyboardInterrupt:
          break
#process the lists of points and time intervals as you so choose
Thanks for the help!
Paul