SRF04 Ultrasonic Rangefinder Unresponsive

[geeknerd99]

tried it. It is now official that we are not gettting any feedback...

[basicxman]

i have an SRF04 but also an SRF08, way better!!! and not to mention its controlled by i2c also it has a built in light sensor (CdS cell)

[jgannon]

Originally Posted by geeknerd99

tried it. It is now official that we are not gettting any feedback...

I'm still not totally convinced. As Steve pointed out, the return pulse is very short, and it's possible that the pulse is coming and going faster than even the fast loop can keep up with. To be totally sure, could you set it up as an interrupt, and then see if you ever trigger it?

[geeknerd99]

It says that if there is no "echo," it won't timeout until 18 ms have passed. I'm sure the fast routine loops faster than 18 ms.

[dcbrown]

how about something like this. It should fire a ~20us drive pulse and then listen on the echo line. The echo line should be asserted shortly after the sonar is fired and remain high until the first echo is detected -or- no echo and the line will drop in 36ms.

void ping()
{

unsigned int count;
char usec;
#define drive_pin rc_dig_in01
#define echo_pin  rc_dig_in02

    //~20uS pulse out
    drive_pin = 1;
    for (usec=20; --usec != 0; )
    {
	Nop();
	Nop();
	Nop();
	Nop();
	Nop();
    }
    drive_pin = 0;

    //echo pulse should start shortly... timeout in ~20ms
    count = 35500;
    while(echo_pin == 0)
    {
	count++;
	if (count == 0)
	{
	    printf( "whoa, where'd the pulse go?\n");
	    return;
	}
     }

     // ok, count the pulse width, count*2 is approx. uSec.
    count = 0;
    while (echo_pin != 1)
    {
	Nop(); Nop(); Nop(); Nop();
	count++;
            if (count == 0) break;
    }
    printf( "count = %d\n", count );
    return;
}

[Gdeaver]

You could always fire up Easy C and check the operation with a Known working code.

[the401tauntaun]

thanks a lot for your help! I will try this tuesday, when I can go back to the shop.

[Qbranch]

Or you could try my single-pin ultrasonic driver.

-q