MATLAB Examples

Simultaneously Acquire and Generate Arbitrary Periodic Waveforms using Digilent® Analog Discovery™

This example shows how to use the function generator to generate an arbitrary waveform function at a rate of 1 KHz and record data at the same time, using an analog input channel. The output voltage-range of the outgoing signal is -5.0 to +5.0 volts. This example uses the session-based interface with Digilent Analog Discovery hardware.

Contents

Discover Digilent devices

Discover Digilent devices connected to your system using daq.getDevices

daq.getDevices()
ans = 

Data acquisition devices:

index   Vendor    Device ID                            Description                           
----- ----------- --------- -----------------------------------------------------------------
1     digilent    AD1       Digilent Inc. Analog Discovery Kit Rev. C
2     directsound Audio0    DirectSound Primary Sound Capture Driver
3     directsound Audio1    DirectSound Primary Sound Driver

Create a session

s = daq.createSession('digilent')
s = 

Data acquisition session using Digilent Inc. hardware:
   Will run for 1 second (10000 scans) at 10000 scans/second.
   No channels have been added.
   

Add a function generator channel

Add a function generator channel with device ID AD1 and channel ID 1. Set the waveform type to Arbitrary.

fgenCh = addFunctionGeneratorChannel(s, 'AD1', 1, 'Arbitrary')
fgenCh = 

Data acquisition arbitrary waveform generator '1' on device 'AD1':

       WaveformData: [4096x1 double]
              Range: -5.0 to +5.0 Volts
     TerminalConfig: SingleEnded
               Gain: 1
             Offset: 0
          Frequency: 4096
       WaveformType: Arbitrary
     FrequencyLimit: [0.0001 25000000.0]
               Name: ''
                 ID: '1'
             Device: [1x1 daq.di.DeviceInfo]
    MeasurementType: 'Voltage'


Define the waveform function to be a sum of sinusoids

The function generator produces periodic outputs by repeatedly generating the contents of its buffer (4096 points). A waveform is constructed to fill this buffer without repeating.

buffersize = 4096;
len = buffersize + 1;

f0 = 1;
f1 = 1 * f0;
f2 = 2 * f0;
f3 = 3 * f0;

waveform  = sin(linspace(0, 2*pi*f1, len)) + ...
            sin(linspace(0, 2*pi*f2, len)) + ...
            sin(linspace(0, 2*pi*f3, len));

A = 5;
waveform = A*waveform./max(abs(waveform));
waveform(end) = [];

Set the waveform data of the channel

fgenCh.WaveformData = waveform;

Set the frequency of the channel to 1 KHz

frate = 1000;
fgenCh.Frequency = frate;

Add an analog input channel

Add an analog input channel with device ID AD1 and channel ID 1. Set the measurement type to Voltage.

aiCh = addAnalogInputChannel(s, 'AD1', 1, 'Voltage')
aiCh = 

Data acquisition analog input voltage channel '1' on device 'AD1':

       Coupling: DC
 TerminalConfig: Differential
          Range: -25 to +25 Volts
           Name: ''
             ID: '1'
         Device: [1x1 daq.di.DeviceInfo]
MeasurementType: 'Voltage'


Define the rate of the acquisition for the session

Acquire data at a higher rate than the highest frequency in the generated waveform (oversample by a factor of 50)

oversamplingratio = 50;
nyquistrate = 2 * frate;
s.Rate = oversamplingratio * nyquistrate;

Define the duration of the acquisition/generation for the session

s.DurationInSeconds = 3;

Generate a periodic waveform function and record input simultaneously

[data, timestamps] = startForeground(s);

Plot waveform function to be generated by the function generator

% Plot parameters
k = 5;
period = 1/frate;
numperiods = k * period;

% Desired waveform
wavedesired = repmat(waveform', k, 1);
tsamples = linspace(0, numperiods, k * buffersize)';

fig = figure;
subplot(311)
plot(tsamples, wavedesired);
xlabel('Time (seconds)'); ylabel('Voltage (Volts)');
title('Desired Waveform: sin(2\pi*1000t) + sin(2\pi*2000t) + sin(2\pi*3000t)');
axis([0 numperiods -A A])

% Acquired waveform
subplot(312)
plot(timestamps, data);
xlabel('Time (seconds)'); ylabel('Voltage (Volts)');
title('Acquired Waveform');
axis([0 numperiods -A A])

% Frequency-Domain Plot (using fft)

L = 2 * oversamplingratio * buffersize;
Fs = s.Rate;
NFFT = 2^nextpow2(L);
Y = fft(data, NFFT)/L;
f0 = (Fs/2) * linspace(0, 1, NFFT/2 + 1);

plotScaleFactor = 12;
plotRange = NFFT / 2; % Plot is symmetric about n/2
plotRange = floor(plotRange / plotScaleFactor);

Yplot = Y(1:plotRange);
fplot = f0(1:plotRange);

% Plot single-sided amplitude spectrum.
subplot(313)
stem(fplot, 2*abs(Yplot));
title('Single-Sided Amplitude Spectrum of Waveform')
xlabel('Frequency (Hz)')
ylabel('|Y(f)|')
axis tight