Random output on decoding time from LTC audio using arduino UNO

Question

I am a newbie in Arduino and I am trying to decode time from ltc audio. For this I got Arduino UNO.

I got a sample code from here.. Here my code:

#define icpPin 8 // ICP input pin on arduino
#define one_time_max 588 // these values are setup for NTSC video
#define one_time_min 422 // PAL would be around 1000 for 0 and 500 for 1
#define zero_time_max 1080 // 80bits times 29.97 frames per sec
#define zero_time_min 922 // 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 bit_time;
volatile boolean valid_tc_word;
volatile boolean ones_bit_count;
volatile boolean tc_sync;
volatile boolean write_tc_out;
volatile boolean drop_frame_flag;
volatile byte total_bits;
volatile byte current_bit;
volatile byte sync_count;
volatile byte tc[8];
volatile char timeCode[11];
/* ICR interrupt vector */
ISR(TIMER1_CAPT_vect)
{
 //toggleCaptureEdge
 TCCR1B ^= _BV(ICES1);
 //Serial.println("Inter");
 bit_time = ICR1;
 //resetTimer1
 TCNT1 = 0;
if ((bit_time < one_time_min) || (bit_time > zero_time_max)) // get rid of anything way outside the norm
 {
 //Serial.println(bit_time, DEC);
 total_bits = 0;
 }
 else
 {
 if (ones_bit_count == true) // only count the second ones pluse
 ones_bit_count = false;
 else
 { 
 if (bit_time > zero_time_min)
 {
 current_bit = 0;
 sync_count = 0;
 }
 else //if (bit_time < one_time_max)
 {
 ones_bit_count = true;
 current_bit = 1;
 sync_count++;
 if (sync_count == 12) // part of the last two bytes of a timecode word
 {
 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++)
 {
 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
 timeCode[9] = (tc[1]&0x03)+0x30; // 10's of frames
 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
*/
 timeCode[9] = ((tc[0]&0xF0)>>4)+0x30; // user bits 8
 timeCode[8] = ((tc[1]&0xF0)>>4)+0x30; // user bits 7
 timeCode[7] = ((tc[2]&0xF0)>>4)+0x30; // user bits 6
 timeCode[6] = ((tc[3]&0xF0)>>4)+0x30; // user bits 5
 timeCode[5] = '-';
 timeCode[4] = ((tc[4]&0xF0)>>4)+0x30; // user bits 4
 timeCode[3] = ((tc[5]&0xF0)>>4)+0x30; // user bits 3
 timeCode[2] = '-';
 timeCode[1] = ((tc[6]&0xF0)>>4)+0x30; // user bits 2 
 timeCode[0] = ((tc[7]&0xF0)>>4)+0x30; // user bits 1
 drop_frame_flag = bit_is_set(tc[1], 2);
 write_tc_out = true;
 }
 }
}
void setup()
{
 Serial.begin(9600);
 pinMode(8, 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;
 Serial.println("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)
 //Serial.print("TC-[df] ");
 //else
 //Serial.print("TC-[nd] ");
 Serial.print((char*)timeCode);
 //Serial.print("\r");
 }
}

I am generating LTC audio from this link. On running my code I am getting this output:-

Finished setup
?>-00-0000??-??-77=??>-??-;?????-??-?>???>-:?-=????>-??-?=???>-;=-??5>?>-;=-??=7?>-?;-??=>?>-?:-??=7?>-;=-??>??>-;;-??=7??-?=-=7?>?>->7-?????>-;;-??=7?>-;>->??:??-?=-7????>-;?-??5>?>-;?-?=?>??-?=-?7>??>-7:-?67=?>-;?-???5?>-;=-7?==?>-;;-??=7?>-7=-??>>?>-:?-7????>-;=-?;;=??-?=->?=5?>-;=-???=?>-;?-?=5>??-?;->=???>-?>-7>;???-?;->????>-;?-?7=??>-;>-??>;?>-;=-;?5>?>-??-=7;7?>-;=-;?=??>-;=-??=7?>-;=-??:??>->7-=?????-?7-=?>>?>-?6-??;>?>-7;-???=?>-??-;=???>-;=-?7=7?>-?=-??>;?>-:?->??

So, can anyone one tell me where is mistake.

Answer 1

((tc[0]&0xF0)>>4)+0x30

Will generate values in the range x30 to x3F, which are 0 to 9 :;<=>? This is what you are seeing in you output (because you are adding in x2D '-')

I'm not sure what you are expecting to see, but as far as I can tell there are no mistakes and your code is working fine.

If you are trying to turn tc[0] into a hex digit then I would use this function

char ToHex (const char input)
{
 char output = '0';
 if (input > 9)
 { 
 output = (input - 10) + 'A';
 }
 else
 {
 output = input + '0';
 }
 return output;
}
char TCToHex (const char input)
{
 return ToHex(((input & 0xF0) >> 4));
}
char* CharToHex(const char input, char buffer[3])
{
 buffer[0] = ToHex((input & 0xF0) >> 4);
 buffer[1] = ToHex((input & 0x0F));
 buffer[2] = '0円'; // Always null terminate a string
 return buffer;
}

So what you will get if you call the functions is

 char buffer[3];
printf("CharToHex 0x%s\n", CharToHex('A', buffer)); //0x41 65 in decimal, ASCII A
printf("TCToHex = 0x%c \n", TCToHex(0x50)); // 5, because this function only takes the high nibble.
printf("ToHex = 0x%c \n", ToHex(0x0f)); // F

Hope that helps.

• tabish: I am trying to send time stamp on serial port. But your code is not working. Any idea?
• Code Gorilla: Unless your timestamp is in the same format as the TC array then no it won't. I'll edit the answer to provide you with a more generic solution too.