[Roger]

Not to be contradictory -- but I guess I may be. I had to dig out our last year's pneumatic code to check how we did it. In autonomous, the routine was called with variable Position either 1 or 0:

   if (Position==1)                          //Open pinchers/release tube?
   {
      relay1_fwd= 1;                         //Pressurize to open
      relay1_rev= 0;                         //This always zero
   }
   else if (Position==0)                     //Close pinchers/pinch tube?
   {
      relay1_fwd= 0;                         //Depressurize to open (release tube)
      relay1_rev= 0;                         //This always zero
   }

The relay1_rev was always zero, and only relay1_fwd switched between one and zero. I always thought it was odd, but hey, it did work.

But another place was in user_routines.c/User_Initialization routine -- make sure your digital_io was set to INPUT:

  digital_io_18 = INPUT;  /* Used for pneumatic pressure switch. */

We also had a slightly different way with the joystick trigger, to click it each time to reverse state:

   if (p2_sw_trig != SqueezeTrigLast)           //Trigger changed state? (squeeze/no squeeze)
      {                                         //Yes:
         if (p2_sw_trig == 1)                   //...Trigger pressed
         {
            SqueezeState= 1 - SqueezeState;     //Toggle state 0 to 1 to 0
         }  
         //printf("SS=%d  fwd=%d  rev=%d",SqueezeState, relay1_fwd, relay1_rev); 
        // Part 2 Open... or... shut???   
         if (SqueezeState==0)                   //Is state to be OPEN?
         {                                      //Yes:
            relay1_fwd= 1;                      //Pressurize
            relay1_rev= 0;                      //This stays zero
            //printf ("OPEN\r\n");
         }
         else                                   //State is NOT OPEN
         {
            relay1_fwd= 0;                      //Depressurize       
            relay1_rev= 0;                      //This stays zero
            //printf ("SHUT\r\n");
         }
         SqueezeTrigLast= p2_sw_trig;           //Save trigger state for next time check
      }

This way you don't have to hold the trig button.

And yes, because programmers are always perfect, have the hardware guys make sure they did everything right.
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Every revolutionary idea seems to evoke three stages of reaction. They may be summed up by the phrases: (1) It's completely impossible. (2) It's possible, but it's not worth doing. (3) I said it was a good idea all along. RIP Arthur C. Clarke