I've managed to adapt some code from the Arduino forums to display timecode on an LCD display.
What I would like some extra help with is first is there a way of defining the one_time_max etc differently depending on the high low state of a pin? This way I could use a switch to change the times so it could switch between NTSC and PAL.
Secondly would anyone be kind enough to explain what is happening in the middle part of this code? I've made some notes but any help would be really appreciated.
Here is a picture of how it's going so far. I'll keep you guys up to date as the project continues :)
[![enter image description here][1]][1]
// Code from forum post Dec 12, 2007
// include the library code:
#include <LiquidCrystal.h>
// initialize the library with the numbers of the interface pins
LiquidCrystal lcd(12, 11, 5, 4, 3, 2);
#define one_time_max 600 // these values are setup for PA video
#define one_time_min 400
// It's the durstion of a one and zero with a little bit of room for error.
#define zero_time_max 1050 //
#define zero_time_min 950 //
#define icpPin 8 // ICP input pin on arduino
//#define one_time_max 475 // these values are setup for NTSC video
//#define one_time_min 300 // PAL would be around 1000 for 0 and 500 for 1
//#define zero_time_max 875 // 80bits times 29.97 frames per sec
//#define zero_time_min 700 // equals 833 (divide by 8 clock pulses)
#define end_data_position 63
#define end_sync_position 77
#define end_smpte_position 80
volatile unsigned int pin = 13;
volatile unsigned int bit_time;
// volatile instructs the variable to be stored in RAM
volatile boolean valid_tc_word;
// boolean can be either of two values true or false but default to false
volatile boolean ones_bit_count;
// boolean can be either of two values true or false but default to false
volatile boolean tc_sync;
// boolean can be either of two values true or false but default to false
volatile boolean write_tc_out;
// boolean can be either of two values true or false but default to false
volatile boolean drop_frame_flag;
// boolean can be either of two values true or false but default to false
volatile byte total_bits; //this stores a an 8-bit unsigned number
volatile byte current_bit; //this stores a an 8-bit unsigned number
volatile byte sync_count; //this stores a an 8-bit unsigned number
volatile byte tc[8]; //this stores a an 8-bit unsigned number
volatile char timeCode[11]; //this stores a an 8-bit unsigned number
/* ICR interrupt vector */
ISR(TIMER1_CAPT_vect) {
//ISR=Interrupt Service Routine, and timer1 capture event
//toggleCaptureEdge
TCCR1B ^= _BV(ICES1);
//toggles the edge that triggers the handler so that the duration of both high and low pulses is measured.
bit_time = ICR1; //this is the value the timer generates
//resetTimer1
TCNT1 = 0;
// Ignore phase changes < time for 1 bit or > time for zero bit (zero bit phase change time is double that of 1 bit)
if ((bit_time < one_time_min) || (bit_time > zero_time_max)) {
// this gets rid of anything that's not what we're looking for
total_bits = 0;
} else {
// If the bit we are reading is a 1 then ignore the first phase change
if (ones_bit_count == true)
// only count the second ones pulse
ones_bit_count = false;
else {
// We have already checked the outer times for 1 and zero bits so no see if the inner time is > zero min
if (bit_time > zero_time_min) {
// We have a zero bit
current_bit = 0;
sync_count = 0; // Not a 1 bit so cannot be part of the 12 bit sync
} else {
// It must be a 1 bit then
ones_bit_count = true; // Flag so we don't read the next edge of a 1 bit
current_bit = 1;
sync_count++; // Increment sync bit count
if (sync_count == 12) {
// part of the last two bytes of a timecode word
// We have 12 1's in a row that can only be part of the sync
sync_count = 0;
tc_sync = true;
total_bits = end_sync_position;
}
}
if (total_bits <= end_data_position) {
// timecode runs least to most so we need
// to shift things around
tc[0] = tc[0] >> 1;
for(int n=1;n<8;n++) {
//creates tc[1-8]
if(tc[n] & 1) tc[n-1] |= 0x80;
tc[n] = tc[n] >> 1;
}
if(current_bit == 1) tc[7] |= 0x80;
}
total_bits++;
}
if (total_bits == end_smpte_position) {
// we have the 80th bit
total_bits = 0;
if (tc_sync) {
tc_sync = false;
valid_tc_word = true;
}
}
if (total_bits <= end_data_position) {
// timecode runs least to most so we need
// to shift things around
tc[0] = tc[0] >> 1;
for(int n=1;n<8;n++) {
//creates tc[1-8]
if(tc[n] & 1) tc[n-1] |= 0x80;
tc[n] = tc[n] >> 1;
}
if(current_bit == 1) tc[7] |= 0x80;
}
total_bits++;
}
if (total_bits == end_smpte_position) {
// we have the 80th bit
total_bits = 0;
if (tc_sync) {
tc_sync = false;
valid_tc_word = true;
}
}
if (valid_tc_word) {
valid_tc_word = false;
timeCode[10] = (tc[0]&0x0F)+0x30;
// frames this converst from binary to decimal giving us the last digit
timeCode[9] = (tc[1]&0x03)+0x30;
// 10's of frames this converst from binary to decimal giving us the first digit
timeCode[8] = ':';
timeCode[7] = (tc[2]&0x0F)+0x30; // seconds
timeCode[6] = (tc[3]&0x07)+0x30; // 10's of seconds
timeCode[5] = ':';
timeCode[4] = (tc[4]&0x0F)+0x30; // minutes
timeCode[3] = (tc[5]&0x07)+0x30; // 10's of minutes
timeCode[2] = ':';
timeCode[1] = (tc[6]&0x0F)+0x30; // hours
timeCode[0] = (tc[7]&0x03)+0x30; // 10's of hours
drop_frame_flag = bit_is_set(tc[1], 2);
//detects whether theree is the drop frame bit.
write_tc_out = true;
}
}
void setup() {
lcd.begin (16, 2);
pinMode(icpPin, INPUT); // ICP pin (digital pin 8 on arduino) as input
bit_time = 0;
valid_tc_word = false;
ones_bit_count = false;
tc_sync = false;
write_tc_out = false;
drop_frame_flag = false;
total_bits = 0;
current_bit = 0;
sync_count = 0;
lcd.print("FINISHED SETUP");
delay (1000);
TCCR1A = B00000000; // clear all
TCCR1B = B11000010; // ICNC1 noise reduction + ICES1 start on rising edge + CS11 divide by 8
TCCR1C = B00000000; // clear all
TIMSK1 = B00100000; // ICIE1 enable the icp
TCNT1 = 0; // clear timer1
}
void loop() {
if (write_tc_out) {
write_tc_out = false;
if (drop_frame_flag)
lcd.print("TC-[df] ");
else
lcd.print("TC-NO DROP FRAME");
lcd.setCursor(0, 1);
lcd.print((char*)timeCode);
lcd.print("\r");
lcd.setCursor(11, 1);
lcd.print("......");
delay (30);
lcd.clear();
}
}
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[1]: https://i.sstatic.net/V6CxE.jpg
