Bass Guitar Tuner

This is a tuner for four-string bass guitars. As i dont play this instrument myself, i built it for a friend. I think it turned out quite good and it works really well. If you liked this project, please consider subscribing to my youtube channel. I plan on making more videos about my creations in the futute.

Thanks!

Step 1: Video Explaining Everything

Step 2: The Final Product

Step 3: CAD / CAM

These are some pictures taken from the model in Fusion 360 and the toolpaths generated for the CNC mill.

Step 4: Building the Case

Here you can see the milling process and the first working version. I didnt have the dust collector turned on during this process, hence why it looks like a mess.

Step 5: The Software

Here are some of the important parts of the software.

It is a little bit messy as it has changed a lot over the development.

At first i just used a fast fourier transform for the frequency detection, but this turned out to be too slow and impercise.

First the sampling function:

void sampleTimerISR() { 
  if(SampleCount != frameSize){
    if(enablePreamp){
      sampleFrame[SampleCount] = adc1_get_raw(ADC1_CHANNEL_0)-signalOffsetPreamp;
      if(sampleFrame[SampleCount] == 511-signalOffsetPreamp) maxScaleCnt ++;
    } 
    else{
      sampleFrame[SampleCount] = adc1_get_raw(ADC1_CHANNEL_3)-signalOffset;
      if(sampleFrame[SampleCount] == 511-signalOffset) maxScaleCnt ++;
    }              
    if((sampleFrame[SampleCount] < zeroLevelTolerance) && (sampleFrame[SampleCount] > zeroLevelTolerance*-1)) zeroSampleCnt ++;
    if(sampleFrame[SampleCount] > lowLevelThreshold) lowLevelCnt ++;
    avgCount += sampleFrame[SampleCount];
    SampleCount++;
  }
  else{
    if(enablePreamp){
      if(avgCount/frameSize > 0) signalOffsetPreamp++;
      else if(avgCount/frameSize < 0) signalOffsetPreamp--;
    }
    else{
      if(avgCount/frameSize > 0) signalOffset++;
      else if(avgCount/frameSize < 0) signalOffset--;
    }
    if(maxScaleCnt > maxScaleSamplesThresshold)  enablePreamp =false;
    if(lowLevelCnt < lowsignalSamplesThresshold)  enablePreamp =true;
    if(zeroSampleCnt > zeroSamplesThreshold){
      disconnectDevice();
      SampleCount =0;
    }
    else{
      timerAlarmDisable(sampleTimer);
      connectDevice();
      frameCollected = true;
    }
    avgCount =0;
    zeroSampleCnt =0;
    lowLevelCnt =0;
    maxScaleCnt =0;
  }
}

Frequency calculation function:

//Autocorrelation based
int FreqDet::calcFreq(int* frame){
    //calculate autocorrelation
    int autocor[frameSize];
    for(int i=0; i < frameSize; i++){
        autocor[i] =0;
        for(int k=0; k < frameSize-i; k++){
            autocor[i] += (frame[k])*(frame[k+i]);    
        } 
    }
    //find indices of peaks in autocorrelation
    int peakIdx[peakSearchCnt];
    peakIdx[0] = 0;//autocorrelation always has  peak at 0 
    int peakCnt =1;
    for(int i =1; i < frameSize-1; i++){
        if(autocor[i-1] < autocor[i] && autocor[i+1] < autocor[i] && autocor[i] > autocor[0]/peakRejectFactor){
            peakIdx[peakCnt] =i;
            peakCnt ++;
        }
        if(peakCnt == peakSearchCnt) break;
    }
    //sort peak-indices by peak-size 
    for (int i = 1; i < peakCnt; i++){
        for (int j = 0; j < peakCnt - i ; j++) {
            if (autocor[peakIdx[j]] < autocor[peakIdx[j + 1]]) {
                int tmp = peakIdx[j];
                peakIdx[j] = peakIdx[j + 1];
                peakIdx[j + 1] = tmp;
            }
        }
    }
    //return freqiencies
    int avgPeriod = peakIdx[1];
    for (int i = 2; i < peakCnt; i++){
        if(peakIdx[i] < peakIdx[1]*i + basePeriodDeviation*i  &&  peakIdx[i] > peakIdx[1]*i - basePeriodDeviation*i ){
            avgPeriod = peakIdx[i]/i;
        }
    }
    return sampFreq/avgPeriod;
}

Display function:

void displayFreq(int f){
  if(f<15 || f == 50){//High Pass filter to display and 50Hz line noise filter
    //display::displayNumber(0);
    display::displayLine();
    display::displayNote(' ');
    display::blinkCenter(false);
    display::displayBar(0x1<<10);
    return;
  }
  int meanFreaq =0;
  if(f >= FREQ_E - 10   &&   f < (FREQ_E+(FREQ_A-FREQ_E)/2)){
    meanFreaq = ema_E.addPoint(f);
    display::displayNumber(meanFreaq);
    display::displayNote('E');
    if(meanFreaq == FREQ_E) display::blinkCenter(false);
    else display::blinkCenter(true);
    display::displayBar(0x1<<((FREQ_E+(FREQ_A-FREQ_E)/2)+3-meanFreaq));
  }
  else if(f >= (FREQ_A-(FREQ_A-FREQ_E)/2)   &&   f < (FREQ_A+(FREQ_D-FREQ_A)/2)){
    meanFreaq = ema_A.addPoint(f);
    display::displayNumber(meanFreaq);
    display::displayNote('A');
    if(meanFreaq == FREQ_A) display::blinkCenter(false);
    else display::blinkCenter(true);
    display::displayBar(0x1<<((FREQ_A+(FREQ_D-FREQ_A)/2)+1-meanFreaq));
  }
  else if(f >= (FREQ_D-(FREQ_D-FREQ_A)/2)   &&   f <= (FREQ_D+10)){
    meanFreaq = ema_D.addPoint(f);
    Serial.println(meanFreaq);
    display::displayNumber(meanFreaq);
    display::displayNote('D');
    if(meanFreaq == FREQ_D) display::blinkCenter(false);
    else display::blinkCenter(true);
    display::displayBar(0x1<<((FREQ_D+10)-meanFreaq));
  }
  else if(f >= FREQ_G - 10  &&  f <= FREQ_G +10){
    meanFreaq = ema_G.addPoint(f);
    display::displayNumber(meanFreaq);
    display::displayNote('G');
    if(meanFreaq == FREQ_G) display::blinkCenter(false);
    else display::blinkCenter(true);
    display::displayBar(0x1<<(FREQ_G+10-meanFreaq));
  }
  else {//some frequenzy not related to a note
    display::displayNumber(f);
    display::displayNote(' ');
    display::blinkCenter(false);
    display::displayBar(0x1<<10);
  }
}