How to get frequency of waveforms measured through the SDK

[arnavguptagenerac]

Hello, 

 

I am trying to get some waveforms from a device to make sure that is outputting what I want. The voltage of the waveform is already confirmed to be done but I do not know how to determine the frequency of the waveform from the SDK. I am using the following code. Any tips?

 

"""
   DWF Python Example
   Author:  Digilent, Inc.
   Revision:  2018-07-19

   Requires:                       
       Python 2.7, 3
"""

from ctypes import *
from dwfconstants import *
import math
import time
import matplotlib.pyplot as plt
import sys
import numpy

if sys.platform.startswith("win"):
    dwf = cdll.dwf
elif sys.platform.startswith("darwin"):
    dwf = cdll.LoadLibrary("/Library/Frameworks/dwf.framework/dwf")
else:
    dwf = cdll.LoadLibrary("libdwf.so")

#declare ctype variables
hdwf = c_int()
sts = c_byte()
hzAcq = c_double(100000)
nSamples = 200000
rgdSamples = (c_double*nSamples)()
cAvailable = c_int()
cLost = c_int()
cCorrupted = c_int()
fLost = 0
fCorrupted = 0

#print(DWF version
version = create_string_buffer(16)
dwf.FDwfGetVersion(version)
print("DWF Version: "+str(version.value))

#open device
print("Opening first device")
dwf.FDwfDeviceOpen(c_int(-1), byref(hdwf))

if hdwf.value == hdwfNone.value:
    szerr = create_string_buffer(512)
    dwf.FDwfGetLastErrorMsg(szerr)
    print(str(szerr.value))
    print("failed to open device")
    quit()

print("Generating sine wave...")
dwf.FDwfAnalogOutNodeEnableSet(hdwf, c_int(0), AnalogOutNodeCarrier, c_bool(True))
dwf.FDwfAnalogOutNodeFunctionSet(hdwf, c_int(0), AnalogOutNodeCarrier, funcSine)
dwf.FDwfAnalogOutNodeFrequencySet(hdwf, c_int(0), AnalogOutNodeCarrier, c_double(1))
dwf.FDwfAnalogOutNodeAmplitudeSet(hdwf, c_int(0), AnalogOutNodeCarrier, c_double(2))
dwf.FDwfAnalogOutConfigure(hdwf, c_int(0), c_bool(True))

#set up acquisition
dwf.FDwfAnalogInChannelEnableSet(hdwf, c_int(0), c_bool(True))
dwf.FDwfAnalogInChannelRangeSet(hdwf, c_int(0), c_double(5))
dwf.FDwfAnalogInAcquisitionModeSet(hdwf, acqmodeRecord)
dwf.FDwfAnalogInFrequencySet(hdwf, hzAcq)
dwf.FDwfAnalogInRecordLengthSet(hdwf, c_double(nSamples/hzAcq.value)) # -1 infinite record length

#wait at least 2 seconds for the offset to stabilize
time.sleep(2)

print("Starting oscilloscope")
dwf.FDwfAnalogInConfigure(hdwf, c_int(0), c_int(1))

cSamples = 0

while cSamples < nSamples:
    dwf.FDwfAnalogInStatus(hdwf, c_int(1), byref(sts))
    if cSamples == 0 and (sts == DwfStateConfig or sts == DwfStatePrefill or sts == DwfStateArmed) :
        # Acquisition not yet started.
        continue

    dwf.FDwfAnalogInStatusRecord(hdwf, byref(cAvailable), byref(cLost), byref(cCorrupted))
    
    cSamples += cLost.value

    if cLost.value :
        fLost = 1
    if cCorrupted.value :
        fCorrupted = 1

    if cAvailable.value==0 :
        continue

    if cSamples+cAvailable.value > nSamples :
        cAvailable = c_int(nSamples-cSamples)
    
    dwf.FDwfAnalogInStatusData(hdwf, c_int(0), byref(rgdSamples, sizeof(c_double)*cSamples), cAvailable) # get channel 1 data
    #dwf.FDwfAnalogInStatusData(hdwf, c_int(1), byref(rgdSamples, sizeof(c_double)*cSamples), cAvailable) # get channel 2 data
    cSamples += cAvailable.value

dwf.FDwfAnalogOutReset(hdwf, c_int(0))
dwf.FDwfDeviceCloseAll()

print("Recording done")
if fLost:
    print("Samples were lost! Reduce frequency")
if fCorrupted:
    print("Samples could be corrupted! Reduce frequency")

f = open("record.csv", "w")
for v in rgdSamples:
    f.write("%s\n" % v)
f.close()
  
plt.plot(numpy.fromiter(rgdSamples, dtype = numpy.float))
plt.show()
 

[attila]

Hi @arnavguptagenerac

The FDwfAnalogOutNodeFunctionSet specifies the AWG signal frequency in Hz, except for random and play mode the update/sample rate, and the FDwfAnalogInFrequencySet the Oscilloscope sampling frequency/rate in Hz.

[arnavguptagenerac]

On 10/7/2022 at 10:33 AM, attila said:

Hi @arnavguptagenerac

The FDwfAnalogOutNodeFunctionSet specifies the AWG signal frequency in Hz, except for random and play mode the update/sample rate, and the FDwfAnalogInFrequencySet the Oscilloscope sampling frequency/rate in Hz.

@attila I understand that I can set the sampling rate and output frequency of the analog channels. I was more wondering if there was anyone to get the frequency value that shows up in the actual waveform application scope. Like the ones you can access under measurements for C1 and C2. I want to try and recieve the frequency value of both channels of the actual waveform I am measuring. 

[attila]

Hi @arnavguptagenerac

Those measurements are performed in the WF application and are not available if the API only from the app's Script tool.
For periodic signals FFT is a preferable method, see: AnalogIn_Frequency.py