This is a quick example of using ctypes and numpy to do data acquisition using National Instrument's NI-DAQmx library. This library allows access to their wide range of data acquisition devices. By using ctypes, we bypass the need for a C compiler. The code below assumes a Windows platform. NI-DAQmx is also available for Linux, but the code below would require a few minor changes, namely loading the shared library and setting the function signatures.
See also Data acquisition with PyUniversalLibrary.
OK, enough talk, let's see the code!
#Acq_IncClk.py
# This is a near-verbatim translation of the example program
# 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_Cfg_Default = int32(-1)
DAQmx_Val_Volts = 10348
DAQmx_Val_Rising = 10280
DAQmx_Val_FiniteSamps = 10178
DAQmx_Val_GroupByChannel = 0
##############################
def CHK(err):
"""a simple error checking routine"""
if err < 0:
buf_size = 100
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
data = numpy.zeros((max_num_samples,),dtype=numpy.float64)
# now, on with the program
CHK(nidaq.DAQmxCreateTask("",ctypes.byref(taskHandle)))
CHK(nidaq.DAQmxCreateAIVoltageChan(taskHandle,"Dev1/ai0","",
DAQmx_Val_Cfg_Default,
float64(-10.0),float64(10.0),
DAQmx_Val_Volts,None))
CHK(nidaq.DAQmxCfgSampClkTiming(taskHandle,"",float64(10000.0),
DAQmx_Val_Rising,DAQmx_Val_FiniteSamps,
uInt64(max_num_samples)));
CHK(nidaq.DAQmxStartTask(taskHandle))
read = int32()
CHK(nidaq.DAQmxReadAnalogF64(taskHandle,max_num_samples,float64(10.0),
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()