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measure time for 1 input

 
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iseron



Joined: 21 Feb 2004
Posts: 12
Location: Santiago - Chile

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measure time for 1 input
PostPosted: Thu Jul 15, 2004 10:30 am     Reply with quote
Hi.

Developing an IR receiver i need to measure the timeof duratio of pulses when receving. ( for a sony protocol)

How can i discriminate between 2 pulses?

For example and 600 ms pulse is a "zero" and a 1200 ms pulse is a "one".

Exists a simplfied code for that?

thnks
ignacio
Ttelmah
Guest
Re: measure time for 1 input
PostPosted: Thu Jul 15, 2004 10:47 am     Reply with quote
iseron wrote:
Hi.

Developing an IR receiver i need to measure the timeof duratio of pulses when receving. ( for a sony protocol)

How can i discriminate between 2 pulses?

For example and 600 ms pulse is a "zero" and a 1200 ms pulse is a "one".

Exists a simplfied code for that?

thnks
ignacio

Use an input supporting 'interrupt on change' (RB4..7). In the interrupt code, if the edge is a rising edge (assuming the electronics decodes the pulses to +ve logic), reset a timer (timer2?). If it is a falling edge, take the reading from the timer. Depending on the setup used for the timer, you have a number proportional to the pulse width.
I have done a similar thing on a 12F675, where five different pulse widths have to be detected, by sitting in a loop (instead of using the interrupt), with:
Code:

#define inp_mask (0x08)

   int timeval;
   int last;
   setup_TIMER_0(RTCC_INTERNAL|RTCC_DIV_16);
   last=GPIO;
   while (last==GPIO) restart_wdt();
   //Here I may have an edge on the incoming signal
   if (GPIO & inp_mask) {
       //Here the input is high
       if (!(last & inp_mask)) {
          // Here I have a rising edge on the pulse train.
          set_timer0(0);
          // Now I time the high pulse
          while (GPIO & inp_mask) {
              if (get_timer0()>=120) break;
          }
          timeval=get_timer0();
          // The timer counts in 16uSec ticks from it's trigger point
          // I can now check this value to see where I should be.
          }
      }

'GPIO', is programmed as the port I am watching, and 'inp_mask' is a mask matching the bit I am watching. 'timeval', counts the width of the pulse in 16uSec 'steps' (using the internal 4MHz oscillator on the 12F675), so for a pulse that is 1/2400th second wide, returns a count of 26. You can just test for the required 'width' to match your needs (in this case the processor is doing nothing else). The interrupt approach, would allow you to be doing other tasks while waiting.

Best Wishes
Guest
Re: measure time for 1 input
PostPosted: Sat Jul 17, 2004 12:56 am     Reply with quote
iseron wrote:
Hi.

Developing an IR receiver i need to measure the timeof duratio of pulses when receving. ( for a sony protocol)

How can i discriminate between 2 pulses?

For example and 600 ms pulse is a "zero" and a 1200 ms pulse is a "one".

Exists a simplfied code for that?

thnks
ignacio


Try Google search: pic ir receiver sircs

Erkki
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