here’s an update on the new additions/approach to the Mellotronium. i’m attempting to redo the SD card routines once i get the functionality added. using the SD library just doesn’t work right when reading byte values at 8kHz. i’ve looked into the WaveHC library with the most success, but had to modify not to use an external DAC. a new wav file playing solution from the SD card will have to be found.

without the clunky SD lib, program space has opened up… a lot of it in fact. now i’ve started using a wavetable. this video just has a single sine wave, but it’s modulate with the LFO and its seven different waveforms not to mention an amplitude modulating ADSR filter.

the breadboard to the side contains an experimental active 2-band EQ (TLO82-based) which needs some work. if anyone has any experience with this, i would love to know why the schematic in the datasheet doesn’t work at all. i wound up having to recall the usage from a different schematic where you make a voltage divider from and peer it into the positive terminal on both opamps. it works… in a way. i think i’ve inverted the wave form or something strange. it also sometimes works better as a radio than an EQ which i think i like. it made for some interesting heterodyning.

here’s a picture of my mobile APRS setup in the Jeep. it’s been a fun project from time to time. eventually, i plan on constructing a 2m vertical antenna to throw on the roof for better satellite reception while being mobile. i’m currently using a high-gain Comet mag-mount which is an excellent antenna. i was actually able to get out over 20 miles the other night on 146.52 with K5YLE using only 5 watts on the FT-60. for satellite reception, i’ll have to do a custom design.

the setup uses the FT-60R packet cable design into my Gentoo Linux laptop (Samsung N210) running soundmodem and Xastir.

two days worth of soldering and layout. it’s a combination of the Magnus Modulus and Rebote delay schematics. i couldn’t get the mixing circuit to really work from the Rebote schematic (an older version) without some serious distortion, so i just kind of reworked it on my own. here’s the schematic. i wouldn’t commit to it 100%, but it’s a start. tomorrow i’ll see if it level from bypass to effect works.

here’s a treat for anyone that’s into the audio side of arduino. it’s an 8-bit two-timer based LFO Generator using timer 0/2 on an ATMega328p. i’m only using timer2 for output in this code. i’ve started implementing the LFO code into my 8-bit melotronium where timer 2 is dedicated for the audio output. in the larger code base, timer0 just stores values in an unsigned integer that the other timer grabs and modulates the output mathematically. for now, this should be a good reference to anyone looking for the outline of an LFO with seven different wave forms.

#include 
#include 

#define cbi(sfr, bit) (_SFR_BYTE(sfr) &= ~_BV(bit))
#define sbi(sfr, bit) (_SFR_BYTE(sfr) |= _BV(bit))

uint8_t sineTable[] = {
  127,130,133,136,139,143,146,149,152,155,158,161,164,167,170,173,176,178,181,184,187,190,
  192,195,198,200,203,205,208,210,212,215,217,219,221,223,225,227,229,231,233,234,236,238,
  239,240,242,243,244,245,247,248,249,249,250,251,252,252,253,253,253,254,254,254,254,254,254,
  254,253,253,253,252,252,251,250,249,249,248,247,245,244,243,242,240,239,238,236,234,
  233,231,229,227,225,223,221,219,217,215,212,210,208,205,203,200,198,195,192,190,187,184,
  181,178,176,173,170,167,164,161,158,155,152,149,146,143,139,136,133,130,127,124,121,118,
  115,111,108,105,102,99,96,93,90,87,84,81,78,76,73,70,67,64,62,59,56,54,51,49,46,44,
  42,39,37,35,33,31,29,27,25,23,21,20,18,16,15,14,12,11,10,9,7,6,5,5,4,3,2,2,1,1,1,0,0,0,
  0,0,0,0,1,1,1,2,2,3,4,5,5,6,7,9,10,11,12,14,15,16,18,20,21,23,25,27,29,31, 33,35,37,39,42,
  44,46,49,51,54,56,59,62,64,67,70,73,76,78,81,84,87,90,93,96,99,102,105,108,111,115,118,121,124
};

uint8_t tWave = 128;
uint8_t sWave = 255;
uint8_t ruWave = 128;
uint8_t rdWave = 128;
uint8_t rWave = 128;

int   i = 0;
int   rate;
int   waveform;
byte  d = HIGH;

void setup() {
  Serial.begin(9600);
  pinMode(6, OUTPUT);
  pinMode(5, OUTPUT);
  pinMode(3, OUTPUT);
  setupTimer();
  OCR0A = 128;
}

void loop() {
  waveform = map(analogRead(0),0,1023,1,7);
  rate = map(analogRead(1),0,1023,255,0);
  OCR0A = rate;
}

ISR(TIMER0_COMPA_vect) {
  if(i == 255) i = 0;
  switch(waveform) {
    case 1:
      analogWrite(3,sine(i));
    break;
    case 2:
      analogWrite(3,triangle(i));
    break;
    case 3:
      analogWrite(3, square(i));
    break;
    case 4:
      analogWrite(3, rampUp(i));
    break;
    case 5:
      analogWrite(3, rampDown(i));
    break;
    case 6:
      analogWrite(3, rand(i));
    break;
    case 7:
      analogWrite(3, white(i));
    break;
  }
  i++;
}

void setupTimer() {
  cli();
/*--- TIMER2 CONFIG ---*/
  sbi(TCCR2A,WGM20);
  sbi(TCCR2A,WGM21);
  cbi(TCCR2A,WGM22);

  sbi(TCCR2B, CS20);
  cbi(TCCR2B, CS21);
  cbi(TCCR2B, CS22);

  sbi(TCCR2A,COM2B1);
  cbi(TCCR2A,COM2B0);

 /*--- TIMER0 CONFIG ---*/
  cbi(TCCR0B,CS00);
  cbi(TCCR0B,CS01);
  sbi(TCCR0B,CS02);

  sbi(TCCR0A, COM0A1);
  cbi(TCCR0A, COM0A0);

  cbi(TCCR0A, WGM00);
  sbi(TCCR0A, WGM01);
  cbi(TCCR0A, WGM02);

  cbi(TIFR0,OCF0A);
  sbi(TIMSK0,OCIE0A);
  sei();
}

int sine(int i) {
  return sineTable[i];
}

int triangle(int i) {
  if(tWave >= 255) d = LOW;
  if(tWave <= 0) d = HIGH;
  if(d == HIGH) tWave++;
  if(d == LOW) tWave--;
  return tWave;
}

int rampUp(int i) {
  ruWave++;
  if(ruWave > 255) ruWave = 0;
  return ruWave;
}

int rampDown(int i) {
  rdWave--;
  if(rdWave < 0) rdWave = 255;
  return rdWave;
}

int square(int i) {
  if(i >= 128) sWave = 255;
  if(i <= 127) sWave = 0;
  return sWave;
}

int rand(int i) {
  if(i == rWave) rWave = random(255);
  return rWave;
}

int white(int i) {
  return random(255);
}

i’ve been pretty Arduino obsessed over the past month. i got in my head this idea about building a midi-controlled digital sampler that uses SD cards for storage after thumbing through the Arduino Cookbook and have finally started to make some headway on the project.

there were some major obstacle to overcome, unfortunately. the first came about when i had some trouble loading the larger libraries (e.g. MIDI.h, SD.h). i spent days trying to figure out what the problem was and even went so far as to update the bootloader to use optiboot. it turned out to be the version of GCC that i was using to compile my sketches. the toolchain setup on Gentoo is no easy task, so i went ahead and just compiled it manually. for those of you tempting to use develop AVR software in a Linux environment, i’d recommend the avr-libc install guide as your path to unbridled success. i myself could never get cross-dev to work with out failing and it needs certain USE flags which it just always overrode when i specified them.

from then on, things were pretty standard. i was able to load SD.h and begin reading files from the card. i used simple voltage dividers to convert the ATMega328′s 5v logic to the SD’s 3.3v like the standard schematic shows and then hacked up the PCMAudio Library to work as i’ve wanted. i borrow some of the techniques from Max’s article on generating real-time audio using PCM. much different than my overall goal, but extremely educational. if you’re baffled by the ATMega328′s use of PWM as i was, Ken Sherif’s article on PWM will clear all that up.

the code’s not worth posting at the moment. it’s a commented out mess of gray. i’ll most likely post it (for my own sake) when i’ve got more of the kinks worked out.

well, not really. feeble attempt and making some sort of microprocessor controlled tempo clock, but a good exercise in the ATMEGA328s finicky behavior. don’t ask me what that squeal is. i think it comes from the way the input was wired up (mistaking the second sleeve as a synonym for ground) coupled with the PWM stream not having a negative offset, but who knows. eventually, i’ll move off the tone() crutch and start working with more interesting DSP. it’ll be nice to start using some of the memory on the chip.

i will also post the schematic for the delay pedal once i’ve got the values i want in it. i won’t have any time nor tools to tear into it until next week though.

Essentially the oBITerator program with aerials instead of actual input signal. Of course, we’ve got to mix in the newly constructed PT2399 pedal. A little work needs to happen in the common-collector preamp which I’m mainly using to lower the input impedance into the delay chip. I’ll be recalculating those values soon as well as switching out a couple of the ceramic caps. They sounded good on the bread board initially, but I’d like to have a little less cutoff. Of course, no experiment would be complete without an LM386-based cigar box amplifier powering a Weber 12″ signature alnico.

here’s a short clip of the delay circuit that i intend to convert to a stomp box. i’m still working out the kinks in the pre-amp stage to solidify the input signal from the guitar though. just a sample though to hear how it might sound with some guitar tones. more soon.

this was a short experiment where i wanted to see how analog AC signals from a guitar were received and converted to digital signals by the ATMEGA328. to “hear” the results along with seeing the numbers as i plucked the strings, i combined digitalWrite() and the tone() functions to output on the same pin giving it a broken-video-game effect just for fun. overall, pretty useless, but the idea of extrapolating the tonal frequency from the input voltage (or at least getting close by using an array of predefined tonal constants) seems feasible enough.

here’s a bit of the code i was using.

const int inputPin = 2;
const int outputPin = 10;

void setup() {
  Serial.begin(9600);
  pinMode(outputPin, OUTPUT);
  pinMode(inputPin, INPUT);
}

void loop() {
  Serial.println(analogRead(inputPin));
  int frequency = map(analogRead(inputPin), 0, 1023, 82.4, 5000);
  int duration = map(analogRead(inputPin), 0, 1023, 0, 1000);
  if(duration != 0) {
    digitalWrite(outputPin, analogRead(inputPin));
    tone(outputPin, frequency, duration);
  }
  delay(duration);
}

Eico Model 460 Oscilloscope Test from abram on Vimeo.

Eico Oscilloscope 460 Manual

Thanks, Daniel.