I've recently purchased a Tsunami (must have been old stock I think!) however I'm having some issues with it.

I cannot seem to get an even frequency sweep - it drops off markedly below ~50Hz and above ~800kHz.

I have an Arduino driven AD9850 DDS module, and that is almost perfectly flat between 10Hz -> 1MHz+

Additionally, when I run the Tsunami test suite, I am seeing failures as below:

Test suite output:

Executing test suite... 
# usb_id = 583430353230158C10 
Read USB ID... OK 
# input_offset = 58 
Test zero offset... OK 
# output_offset_neg = -1270 
Test offset adjustment... FAIL 
output_offset_neg: -1270 is not between -1239 and -839 
# input_amp_6 = 3248 
# input_amp_1 = 605 
# input_amp_0 = 83 
Test amplitude adjustment... FAIL 
input_amp_0: 83 is not between -3280 and -2980 
# input_freq_1k = 1000 
# input_phase_1k = 30 
Test frequency and phase... FAIL 
input_phase_1k: 30 is not between 999 and 1001 
Press enter to rerun test suite.

Are these failures normal? I note that someone else on the forum has reported these too.

I am using what I believe to be the latest libraries as I only downloaded and installed it all during this past week.

Thanks.

Hi,

I'm sorry about the long delay responding; it appears something went wrong with email notifications.

When you say the frequency sweep is uneven, are you looking at output amplitude, or measured input amplitude?

The first failure looks like a minor drift, but the other two are more surprising. Do you have the input and output connected via a BNC cable?

The uneven frequency response was measured using loopback (BNC linking input & output), but I see the same response pattern when I measure a device with a known flat (wideband) response.

For the test suite I also had the input and output connected via a BNC cable.

Some dropoff at high frequency is expected due to the input filters; see this post and this post for an example of the baseline frequency response. Below about 50Hz, the averaging period of the peak detector is too short, leading to a lot of noise.

The test failures are still surprising, though; how are you measuring frequency response?

I am using a sketch based on your sample provided on Github, but I have added some routines to enable selection of fixed frequency, amplitude and also to define the sweep frequency.
This is all controlled from a vb.net application I wrote.
So all this does, is a log sweep (can be 1/3, 1/6, 1/12, 1/24 octave) selectable in my interface (pictured at the bottom of this post)

This is the sketch (I think this is the current sketch - I'm not near my test PC right now).

    /* usage:
 * c responds with connected (used for testing the connection)
 * f 1000 sets the frequency to 1k / ~1Vp
 * d 1000 3 sets frequency to 1k and voltage to ~3Vp
 * s 20 20000 26 3 initiates a 3rd octave sweep of 20 -> 20k at ~3Vp
 * octave values are: 1/3rd (25.9921) | 1/6th (12.2462) | 1/12th (5.9463) | 1/24th (2.930)
 * It's not recommended to use the 1/24th option as it creates far too many points
 * The amplitude of the sweep is output in dBu
 * At initial startup, the generator is set to 1kHz / 2Vp
 */
#include <SPI.h>
#include <tsunami.h>
#define MAXBUF 40

double freqValue = 0;
double freqStart = 0;
double freqEnd = 0;
double freqStep = 0;
double freq = 0;
double Volts = 0;
double outputVolts = 0;
char freqStr[MAXBUF];
int bufPos = 0;
char byteIn = 0;

void setup() {
  // Initialize the Tsunami
  Serial.begin(115200);
  while (!Serial)
  {}
  Serial.println("Initialising...");
  Tsunami.begin();
  //Tsunami.reset(false);
  Tsunami.setAmplitude(2000); // 2Vp
  Tsunami.setFrequency(0, 1000.0);
  // Tsunami.enableSignOutput();
  memset(freqStr, 0, sizeof(freqStr));
}

void fixedFreq() {
  char *fEnd1, *fEnd2;
  freq = abs(strtod(freqStr + 2, &fEnd1));
  outputVolts = abs(strtod(fEnd1, &fEnd2));
  if (outputVolts >= 5) {
    outputVolts = 5;
  }
  outputVolts = outputVolts * 1000;
  Tsunami.setAmplitude(outputVolts);
  Tsunami.setFrequency(freq);
  Serial.print("Set frequency to: ");
  Serial.println(freq);
  Serial.print("Set voltage to: ");
  Serial.println(outputVolts);
  memset(freqStr, 0, sizeof(freqStr));
  byteIn = 0;
  bufPos = 0;
}

void loop() {
  while (Serial.available())
  {
    byteIn = Serial.read();
    if (bufPos < sizeof(freqStr))
      freqStr[bufPos++] = byteIn;
    else
    {
      bufPos = 0;
      byteIn = 0;
      memset(freqStr, 0, sizeof(freqStr));
      Serial.println("Error: Command too long. Ignored.");
    }
  }
  if (byteIn == 0x0a) {
    switch (freqStr[0]) {
      // fixed frequency
      case 'c': // check if connected
        Serial.println("Connected");
        break;
      case 'd': // assign static frequency and amplitude
        fixedFreq();
        break;
      case 'f': // 1kHz tone at fixed amplitude
        freqStart = 0;
        freqEnd = 0;
        freqStep = 0;
        freqValue = strtod(freqStr + 2, NULL);
        Serial.print("Frequency ");
        Serial.print(freqValue);
        Serial.print(" Voltage ");
        Serial.println("1000");
        Tsunami.setFrequency(freqValue);
        Tsunami.setAmplitude(1000);
        break;
      case 's': // sweep
        freqValue = 0;
        delay(500);
        mySweep();
        break;
      default:
        Serial.println("Unknown command");
    }
    memset(freqStr, 0, sizeof(freqStr));
    byteIn = 0;
    bufPos = 0;
  }
}

void mySweep() {
  freqValue = 0;
  delay(500);
  char *fEnd1, *fEnd2;
  freqStart = abs(strtod(freqStr + 2, &fEnd1));
  freqEnd = abs(strtod(fEnd1, &fEnd2));
  freqStep = abs(strtod(fEnd2, &fEnd1));
  outputVolts = abs(strtod(fEnd1, &fEnd2));
  if (outputVolts >= 5) {
    outputVolts = 5;
  }
  outputVolts = outputVolts * 1000;
  Tsunami.setAmplitude(outputVolts);
  delay(50);
  if (freqStep == 0) {
    Serial.println("Error: Please select sweep type");
  }
  Serial.println("# Sweep:");
  Serial.print("# Start: ");
  Serial.print(freqStart);
  Serial.print(" End: ");
  Serial.print(freqEnd);
  Serial.print(" Octave: ");
  Serial.print(freqStep);
  Serial.print(" Output Voltage: ");
  Serial.print(outputVolts);
  Serial.println("");
  for (double freq = freqStart; freq < freqEnd; freq = freq + (freq / 100) * freqStep) {
    Tsunami.setFrequency(freq);
    if (freq <= 1000) {
      delay(500);
    }
    delay(10);
    // read voltage and convert to mV
    double mVoltsPk = Tsunami.measurePeakVoltage();
    double milliVolts = (mVoltsPk / 1000);
    // convert mV to RMS
    double mVoltsRMS = (milliVolts * 0.7071);
    // convert RMS to dBu
    double logV = 20 * log10(mVoltsRMS / 0.775);
    delay(10);
    Serial.print(freq);
    Serial.print(",");
    Serial.println(logV);
  }
  Serial.println("# end");
}

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