Somewhere between the Omnichord and the Stylophone lies this thing... simple but suprisingly effective... a PIC16F688 microcontroller, 2 shift registers IC's, 36 switches and a bunch of wire. The buttons select major/minor/maj7/min7/7/dim/aug chords based on any root note, and you "strum" across 3-4 octaves of notes from the chord by touching bits of exposed wire with a "stylus". The output is all MIDI (circuit makes no sound by itself) and Reason is being used here for sounds.
Note - If you are new to PIC stuff and want to make your own version of this project, remember you will need some way to program the PIC chip (its like a tiny computer and it comes without any software installed). The code is included below, but you'll need to compile it (using the free SourceBoost compiler) and "burn" it to the PIC... you can buy a programmer (e.g. PICkit2) or maybe borrow one. If there is enough demand I might be able to provide pre-programmed PIC16F688's for this, or my other PIC projects. Drop me a message if you'd be interested.
Schematic
The business end...
The mess on the back...
How it works (if you are interested)...
It's the tried and trusted principle of the keyboard matrix - the 74HC595 IC's are "shift registers" which are simply used to scan a single "on" bit across 16 lines, one at a time (all 16 are used for the stylus, the first 12 are used for the columns of the kepad). The program running on the PIC chip reads the voltage coming back from each row of the keypad and also from the stylus. Since the program knows which one of the 16 shift register outputs it has switched "on" at any moment in time it then knows which buttons are pressed / which "strings" the stylus is touching at any moment in time by which input lines (if any) it reads the voltage back on. The rest is down to the program code to convert this info into MIDI notes and send them to a synth. One other important things are the 10k "pull down" resistors on each of the 3 keyboard rows and the stylus line... they make sure that an unconnected line settles at 0V rather than reading spurious random values.
The source code
// STRUM CHORD CONTROLLER
// (c) 2010 J.Hotchkiss
// SOURCEBOOST C FOR PIC16F688
#include <system.h>
#include <memory.h>
// PIC CONFIG
#pragma DATA _CONFIG, _MCLRE_OFF&_WDT_OFF&_INTRC_OSC_NOCLKOUT
#pragma CLOCK_FREQ 8000000
// Define pins
#define P_CLK porta.2
#define P_DS portc.0
#define P_STYLUS portc.1
#define P_HEARTBEAT portc.2
#define P_KEYS1 portc.3
#define P_KEYS2 porta.4
#define P_KEYS3 porta.5
typedef unsigned char byte;
// Chord types
enum {
CHORD_NONE,
CHORD_MAJ,
CHORD_MIN,
CHORD_DOM7,
CHORD_MAJ7,
CHORD_MIN7,
CHORD_AUG,
CHORD_DIM
};
// special note value
#define NO_NOTE 0xff
//byte silent[1] = {NO_NOTE};
// Define the chord structures
byte maj[3] = {0,4,7};
byte min[3] = {0,3,7};
byte dom7[4] = {0,4,7,10};
byte maj7[4] = {0,4,7,11};
byte min7[4] = {0,3,7,10};
byte dim[3] = {0,3,6};
byte aug[3] = {0,3,8};
// Define the MIDI root notes mapped to each key
byte roots[16]={36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51};
// bit mapped register of which strings are currently connected
// to the stylus (notes triggered when stylus breaks contact
// with the strings)
unsigned long strings =0;
// Notes for each string
byte notes[16] = {0};
// current chord type
byte lastChordType = CHORD_NONE;
// current root note
byte lastRoot = NO_NOTE;
////////////////////////////////////////////////////////////
// INITIALISE SERIAL PORT FOR MIDI
void init_usart()
{
pir1.1 = 1; //TXIF transmit enable
pie1.1 = 0; //TXIE no interrupts
baudctl.4 = 0; // synchronous bit polarity
baudctl.3 = 1; // enable 16 bit brg
baudctl.1 = 0; // wake up enable off
baudctl.0 = 0; // disable auto baud detect
txsta.6 = 0; // 8 bit transmission
txsta.5 = 1; // transmit enable
txsta.4 = 0; // async mode
txsta.2 = 0; // high baudrate BRGH
rcsta.7 = 1; // serial port enable
rcsta.6 = 0; // 8 bit operation
rcsta.4 = 0; // enable receiver
spbrgh = 0; // brg high byte
spbrg = 15; // brg low byte (31250)
}
////////////////////////////////////////////////////////////
// SEND A MIDI BYTE
void send(unsigned char c)
{
txreg = c;
while(!txsta.1);
}
////////////////////////////////////////////////////////////
// CONTINUOUS CONTROLLER MESSAGE
void sendController(byte channel, byte controller, byte value)
{
P_HEARTBEAT = 1;
send(0xb0 | channel);
send(controller&0x7f);
send(value&0x7f);
P_HEARTBEAT = 0;
}
////////////////////////////////////////////////////////////
// NOTE MESSAGE
void startNote(byte channel, byte note, byte value)
{
P_HEARTBEAT = 1;
send(0x90 | channel);
send(note&0x7f);
send(value&0x7f);
P_HEARTBEAT = 0;
}
////////////////////////////////////////////////////////////
// CALCULATE NOTES FOR A CHORD SHAPE AND MAP THEM
// TO THE STRINGS
void changeToChord(int root, int which)
{
int i,j,len=0;
byte *struc = maj;
byte chord[16];
if(CHORD_NONE == which || NO_NOTE == root)
{
// stop playing
for(i=0;i<16;++i)
chord[i] = NO_NOTE;
}
else
{
// select the correct chord shape
switch(which)
{
case CHORD_MIN:
struc = min;
len = sizeof(min);
break;
case CHORD_DOM7:
struc = dom7;
len = sizeof(dom7);
break;
case CHORD_MAJ7:
struc = maj7;
len = sizeof(maj7);
break;
case CHORD_MIN7:
struc = min7;
len = sizeof(min7);
break;
case CHORD_AUG:
struc = aug;
len = sizeof(aug);
break;
case CHORD_DIM:
struc = dim;
len = sizeof(dim);
break;
case CHORD_MAJ:
default:
struc = maj;
len = sizeof(maj);
break;
break;
}
// fill the chord array with MIDI notes
int from = 0;
for(i=0;i<16;++i)
{
chord[i] = root+struc[from];
if(++from >= len)
{
root+=12;
from = 0;
}
}
}
// stop previous notes from playing if they are not a
// part of the new chord
for(i=0;i<16;++i)
{
if(notes[i] != NO_NOTE)
{
// check to see if it is part of the new chord
byte foundIt = 0;
for(j=0;j<16;++j)
{
if(chord[j] == notes[i])
{
foundIt = true;
break;
}
}
// if not, then make sure its not playing
if(!foundIt)
{
startNote(0, notes[i], 0);
}
}
}
// store the new chord
for(i=0;i<16;++i)
notes[i] = chord[i];
}
////////////////////////////////////////////////////////////
// POLL KEYBOARD MATRIX AND STRINGS
void pollIO()
{
// clock a single bit into the shift register
P_CLK = 0;
P_DS = 1;
P_CLK = 1;
P_DS = 0;
// get ready to scan
int root = NO_NOTE;
int chordType = CHORD_NONE;
unsigned long b = 1;
// scan for each string
for(int i=0;i<16;++i)
{
// clock pulse to shift the bit (note that
// the first bit does not appear until the
// second clock pulse, since we tied shift and store
// clock lines together)
P_CLK = 0;
P_CLK = 1;
// did we get a signal back on any of the
// keyboard scan rows?
if(P_KEYS1 || P_KEYS2 || P_KEYS3)
{
// have we decided on the root note yet?
if(NO_NOTE == root)
{
// look up the root note
root = roots[15-i];
// get the correct chord shape
switch(
(P_KEYS1? 0b100:0)|
(P_KEYS2? 0b010:0)|
(P_KEYS3? 0b001:0))
{
case 0b111:
chordType = CHORD_AUG;
break;
case 0b110:
chordType = CHORD_DIM;
break;
case 0b100:
chordType = CHORD_MAJ;
break;
case 0b101:
chordType = CHORD_MAJ7;
break;
case 0b010:
chordType = CHORD_MIN;
break;
case 0b011:
chordType = CHORD_MIN7;
break;
case 0b001:
chordType = CHORD_DOM7;
break;
default:
chordType = CHORD_NONE;
break;
}
}
}
// now check whether we got a signal
// back from the stylus (meaning that
// it's touching this string)
byte whichString = 15-i;
if(P_STYLUS)
{
// string is being touched... was
// it being touched before?
if(!(strings & b))
{
// stop the note playing (if
// it is currently playing). When
// stylus is touching a string it
// is "damped" and does not play
// till contact is broken
if(notes[whichString] != NO_NOTE)
{
startNote(0, notes[whichString], 0);
}
// remember this string is being touched
strings |= b;
}
}
// stylus not touching string now, but was it
// touching the string before?
else if(strings & b)
{
// start a note playing
if(notes[whichString] != NO_NOTE)
{
startNote(0, notes[whichString], 127);
}
// remember string is not being touched
strings &= ~b;
}
// shift the masking bit
b<<=1;
}
// has the chord changed?
if(chordType != lastChordType || root != lastRoot)
{
// change to the new chord
lastChordType = chordType;
lastRoot = root;
changeToChord(root, chordType);
}
}
void main()
{
// osc control / 8MHz / internal
osccon = 0b01110001;
// timer0... configure source and prescaler
option_reg = 0b10000011;
cmcon0 = 7;
// configure io
trisa = 0b00110000;
trisc = 0b00001010;
ansel = 0b00000000;
// initialise MIDI comms
init_usart();
// initialise the notes array
memset(notes,NO_NOTE,sizeof(notes));
for(;;)
{
// and now just repeatedly
// check for input
pollIO();
}
}
Saturday, 6 March 2010
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I'd be interested in a pre-programmed pic for this project and the beancan sequencer too!
ReplyDeleteCool... I listed some on ebay
ReplyDeletehttp://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=150426687494
Hey,
ReplyDeleteI live in New Zealand and am very interested in this project. So far I've had a lot of soldering experience in making guitar pedals and such but no programming experience what so ever.
Could I get you to ship me a pre-programmed chip all the way on the otherside of the globe here?
Thanks, Louis
Hey Louis that should be fine.. give me a couple of weeks to get somethng sorted out Cheers J
ReplyDeleteDid you ever get a pre-programmed chip? I'm interested as well!
ReplyDeleteI made one, I'm now building a man sized version with parts from a PC keyboard and brass rods as the "strings".
ReplyDeletePlanning to incorporate a VS1103b as a built-in synth.
Awesome! any pics or clips?
ReplyDeleteI'll try once it's near completion, the VS1103b is a separate module for the moment.
ReplyDeletep.s. i'm logged in via yahoo as Dave, but I can't leave a message thru my login???
excuse a question, I can do this project with another processor than the PIC?. if you can answer in this way to watch
ReplyDelete