From: tnp@invalid.invalid   
      
   On 24/03/2024 09:39, Theo wrote:   
   > The Natural Philosopher  wrote:   
   >> It would seem from the pin states that it gets permanently stuck in   
   >>   
   >> while(!gpio_get(ULTRASONIC_IN))   
   >>                  ;   
   >>   
   >> Which as understand it is waiting for the module (HCSR04) to *start* to   
   >> send a pulse.   
   >   
   > Can you scope it to see if the module is actually sending a pulse?   
   >   
   I could, but in fact it was easier to simply look at it in 'stuck' mode   
   with a DVM.   
      
   > Is the pulse perhaps too short for the Pico to detect?  eg if the loop or   
   > gpio_get() function took some time, it could be the signal goes 0-1-0 in the   
   > middle of a loop iteration and so the gpio_get() never sees it go 1.   
   >   
   As you can see from my last reply that is roughly where I am headed. Or   
   similar. Lacking full ICE., its all a bit 'poke the black box with   
   different sized sticks, and try and infer from what it does, what is   
   happening inside it'   
      
   I think this must be where it sticks, because this is the only infinite   
   loop with both input and output to the module in a low state, which is   
   what I measured:   
      
   	gpio_put(ULTRASONIC_OUT,1);   
   	sleep_us(10);   
   	gpio_put(ULTRASONIC_OUT,0); //reset the input   
   	// wait for echo pulse start   
   	while(!gpio_get(ULTRASONIC_IN))   
   		;   
      
   I.e that it (allegedly) sends a 10µs wide high pulse, and then waits for   
   that to trigger a response from the unit, but that response never happens.   
      
   However that should not vary with the echo *delay*, and a longer target   
   distance seems to improve things..   
      
   ...unless, thinking a bit more, the pulse is so short it comes *and*   
   goes inside that loop, as you suggested.. it certainly should *not*  be,   
   as even on a few cm of target distance, its hundreds of microseconds (i   
   make it 58µs per cm roughly)   
      
   > Theo   
      
   --   
   “It is dangerous to be right in matters on which the established   
   authorities are wrong.”   
      
   ― Voltaire, The Age of Louis XIV   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)