Here’s my Arduino code so far:

#include <SPI.h>

#define PIN_SCK          13             // SPI clock
#define PIN_MISO         12             // SPI data input
#define PIN_MOSI         11             // SPI data output
#define PIN_SS1          10             // SPI hardware default SS pin, 4021
#define PIN_595_1        9              // SPI 74HC595

// result byte for 4021
byte buttons8;

// global vars for button timeout and debounce
long button1timeout = 0;
long button2timeout = 0;
long debounce = 200;

void setup() {
  Serial.begin(9600);
  SPI.begin();

  // set all IC select pins HIGH
  digitalWrite(PIN_SS1,HIGH);
  pinMode(PIN_595_1, OUTPUT);
  digitalWrite(PIN_595_1,HIGH);
}

void loop() {

  // SS1 = HIGH -> 4021 is gathering data from parallel inputs

  // select 595
  digitalWrite(PIN_595_1,LOW);

  // send BIN number to 595 to light 1 LED (not necessarily the 1 example LED on the schematic)
  SPI.transfer(B00000100);

  // deselect 595
  digitalWrite(PIN_595_1,HIGH);

  // select 4021
  digitalWrite(PIN_SS1,LOW);
  // read CD4021 IC
  buttons8 = SPI.transfer(0x00);

  // button functions and debounces
  // needs refactoring for smaller footprint
  if((B10000000 & buttons8) && (millis() - button1timeout > debounce)) {
    Serial.println("but1");
    button1timeout = millis();
  }
  if((B01000000 & buttons8) && (millis() - button2timeout > debounce)) {
    Serial.println("but2");
    button2timeout = millis();
  }

  // deselect 4021
  digitalWrite(PIN_SS1,HIGH);
}

Setup as described in the Arduino tutorial. Reconnect the clock, the MOSI and the slaveselect as the #defines in the following code. And you’re all set.

#include

#define PIN_SCK          13             // SPI clock
#define PIN_MISO         12             // SPI data input
#define PIN_MOSI         11             // SPI data output
#define PIN_SS1          10             // SPI hardware default SS pin

void setup() {
  Serial.begin(9600);
  SPI.begin();
}

void loop() {
  digitalWrite(PIN_SS1,HIGH);

  // while gathering info from parallel inputs
  // do some other processing
  // for now I'll use
  delayMicroseconds(200);

  // select PIN_SS1 CD4021 IC
  digitalWrite(PIN_SS1,LOW);
  // read byte from CD4021 IC
  Serial.println(SPI.transfer(0x00),BIN);
}

tip: buy some resistor arrays instead of all individual resistors

Speed up

In the LCD3Wire library, I removed two delays:

131c131
<   //delay(1);
---
>   delay(1);
155c155
<   //delayMicroseconds(1);
---
>   delayMicroseconds(10);

This gives a good speed increase when using the LCD3Wire library. Furthermore, reading this post (http://solar-blogg.blogspot.com/2009/02/displaying-custom-5×8-characters-on.html) I copied the code to the Arduino and displayed my own custom character (using the LCD3Wire library)

lcd.commandWrite(0x40);
lcd.print(0b00000);
lcd.print(0b00100);
lcd.print(0b00010);
lcd.print(0b11111);
lcd.print(0b00010);
lcd.print(0b00100);
lcd.print(0b00000);
lcd.print(0b00000);
lcd.cursorTo(1,0);
lcd.print(0x00);

And another great LCD speedup trick by designer2k2 on the Arduino forums is to avoid using lcd.cursorTo. Instead use his direct positioning code

http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1240088162

lcd.commandWrite(0x80);                //Line=1, Cursor 0
lcd.commandWrite(0xC0+val);            //Line=2, Cursor val
lcd.commandWrite(0x94+7);              //Line=3, Cursor 7
lcd.commandWrite(0xD4);                //Line=4, Cursor 0

In Thor I recreated the sound of a single analog oscillator like so:

A single Analog Osc generating a sawtooth waveform, no filters, enveloppe only sustain. Sounds… the same! Listen for yourself:

ReasonanalogFLAC by sinneb

This recording was made via the buildin soundcard of my MacBook. Sound quality will improve when better audio interface hardware equipment is being used. The soundcloud conversion didn’t work out, not in PCM nor FLAC…

My soundcloud comment:

Tough upload, still sounds horrible. It’s not that important, just wanted to let you hear the hard-to-hear difference between my own VCO prototype and a construction in Propellerhead Reason’s Thor synthesizer.

vco1_test1

This sawtooth is generated through an orange drop capacitor (sounded better then its wima counterpart) in a 100% analog sound path. Reset pulses are generated by an Arduino and the rise of the sawtooth waveform is controlled by a MCP4921 DAC. Each frequencies requires an exact voltage to level out the sawtooth. I haven’t calibrated these voltages yet so the sawtooth isn’t very precise yet. I like the raw sound though!

The filterpart, 4 pole low pass with resonance. Download LTSpice schematic file:

juno106BetaFilterReplacement_FilterPart (pdf version)

The exponential current source. Leave 10 ohm resistor out when connecting to filterpart. Download LTSpice schematic file:

juno106BetaFilterReplacement_ExpoPart (pdf version)

The VCA of this beta filter was built like the schematic supplied by Mooger5 (check older posts). The redesigned VCA based on a LM13700 should work also (check older posts).

Best sounding values came out like this:

which I, after some thinking, recognized as the original values like in the JUNO6! Very nice! Just had to replace the 100pF capacitor with a 240pF capacitor like in the original. Only thing missing is the “mystery resistor” on the + input of the OTA to ground. For now I just left this res out.

A fitting frequency range for the filter should be achieved by a good control current. According to the IR3109 specifications, transconductance should range from 1µƱ – 10mƱ. The expo converter from the previous post delivers a current ranging from 70nA to 1.65mA which translate to a transconductance of 1.34µƱ to 31mƱ. Ok for now.

I made a mockup of the JUNO6 board and the IR3109 ic:

listen:

Juno106 1pole replacement filter, for now only cutoff by sinneb

btw this is a one pole LP filter, not a two pole

VCF sound like this now:
Juno2poleFilter-v2 by sinneb

and here’s the real 2 pole LP filter:

Juno2poleFilter-v3-real2pole by sinneb

Since I couldn’t figure out a proper way to calculate the cutoff frequency when using different current and resistor combination, I decided to use the default lowpass filter circuit from the LM13700 datasheet.

Hooked my expo converter up to pin 1 (100nA < Iabc < 1.1mA) and started testing. The Vout of this pole is the Vin of the second pole. Unfortunately I only had 1 LM13700 working left, since I blew up all my other’s ;). I experimented a lot with different capacitor and resistor combination and the only ok sounding combination is a 1nF capacitor with 10K big and 220Ohm small resistors. Check the following sound files for the results:

Juno2polefilter by sinneb

Oh, just for fun: a pic of the breadboard in action

left bottom: BA6110 based VCA. Right top: dual 2N3906 based expo converter. Right bottom: Only remaining LM13700 configured as a 2-pole lowpass filter.