Synchronizing the Scope and WaveGen

[ssm]

Dear Help,

I am trying to sync the scope in reading a signal applied using WaveGen for measurement,

here is the code/pseudocode for the scope:

SampleRate = 170.4997

NoSamples = 302

MaxVdd = 0.5

                FDwfAnalogInChannelEnableSet(hdwf, -1, true);

                FDwfAnalogInAcquisitionModeSet(hdwf, acqmodeSingle);

                FDwfAnalogInChannelRangeSet(hdwf, -1, 2);

                FDwfAnalogInFrequencySet(hdwf, SampleRate);

                FDwfAnalogInBufferSizeSet(hdwf, NoSamples);

                FDwfAnalogInTriggerSourceSet(hdwf, trigsrcAnalogOut1);

                //(samples/2-10)/frequency

                FDwfAnalogInTriggerPositionSet(hdwf, (NoSamples/2 -10) / SampleRate);

                FDwfAnalogInTriggerAutoTimeoutSet(hdwf, 1.0);

                FDwfAnalogInTriggerTypeSet(hdwf, trigtypeTransition);

                FDwfAnalogInTriggerLevelSet(hdwf, 0.0);

                FDwfAnalogInTriggerConditionSet(hdwf, trigcondRisingPositive);

                FDwfAnalogInChannelFilterSet(hdwf, -1, filterAverage);

                FDwfAnalogInConfigure(hdwf, true, false);

WaveGen setting

MeasurementTime = NoSamples/SampleRate

CustomSignalFreq = 1/MeasurementTime

                FDwfAnalogOutNodeEnableSet(hdwf, 0, AnalogOutNodeCarrier, true);

                FDwfAnalogOutNodeFunctionSet(hdwf, 0, AnalogOutNodeCarrier, funcCustom);

                FDwfAnalogOutNodeOffsetGet(hdwf, 0, AnalogOutNodeCarrier, &pvoltOutOffset);

                for (int i1=0; i1<NoSamples; i1++) {

                    InputFileSamples[i1]=(OriginalInputFileSamples[i1]-pvoltOutOffset)/EXP->MaxVdd;

                }

                FDwfAnalogOutNodeDataSet(hdwf, 0, AnalogOutNodeCarrier, InputFileSamples, NoSamples);

                FDwfAnalogOutNodeFrequencySet(hdwf, 0, AnalogOutNodeCarrier, CustomSignalFreq);

                FDwfAnalogOutRunSet(hdwf, 0, 1.0 / CustomSignalFreq);

                FDwfAnalogOutNodeAmplitudeSet(hdwf, 0, AnalogOutNodeCarrier, MaxVdd);

                

The Measured Signal is the one read by the scope and it is supposed to be like the signal above it,

please can you tell me what am I doing wrong?

thank you for the help,

ssm

Edited February 3, 2022 by ssm

[attila]

Hi @ssm

The transition triggering is more complex. It requires specifying the TriggerChannel, Level, Hysteresis, Condition, Length, LengthCondition

 

You could simply make the Scope trigger on Wavegen like this:
FDwfAnalogInTriggerSourceSet(hdwf, trigsrcAnalogOut1) # trigger on analog-out 1 start
FDwfAnalogInTriggerPositionSet(hdwf, NoSamples/SampleRate/2) # T0 on left, trigger the first sample
...
FDwfAnalogInConfigure(hdwf, 0, 1);
make sure the analog-in as suffice time for prefill/pretrigger before analog-out is started, use software sleep or AnalogOutWait
FDwfAnalogOutConfigure(hdwf, 0, 1);

 

[ssm]

thank you @attila for the quick reply, sorry I forgot to mention that I do have a pulse at the start the goes up to 0.5V and then -0.5 to trigger the scope, you can notice that from my figure above, I thought this should be good enough to trigger the system 

thanks again

ssm

[ssm]

thank you again for the reply, 

>>make sure the analog-in as suffice time for prefill/pretrigger before analog-out is started, use software sleep or AnalogOutWait

is there a way to estimate this time based on the SampleRate and the measurement time? or it is not relevant? 

 

[ssm]

it worked, thanks a lot, I added Wait(0.1)

[attila]

Hi @ssm

The delay should be at least, prefill = MAX(0, TriggerPosition - NoSamples/SampleRate/2)

For precise measurements to prevent temperature drift, if your application opens and closes the device often or you start this app often, use run or stop as initialization before open. The default shutdown will reduce power consumption app exit or device close but cause slight temperature drift.
dwf.FDwfParamSet(DwfParamOnClose, c_int(0)) # 0 = run, 1 = stop, 2 = shutdown
The first open or offset change should wait 1-2 seconds for these to stabilize, or 10-20 minutes to reach stable operation temp.