==== PID-functions ====

Set of helper functions to initiate and update a PID control loop 

=== Description ===

<code>PID_new( pid[], Float:set, Float:out ) // set up new PID</code>
<code>PID_dir( pid[], direction ) // set direction of control</code>
<code>PID_set( pid[], Float:set ) // adjust the target value</code>
<code>PID_tune( pid[], Float:Kp, Float:Ki, Float:Kd ) // set the P, I, D parameters</code>
<code>PID_limits( pid[], Float:min, Float:max ) // set the control range</code>
<code>PID_update( pid[], Float:in ) // update PID with feedback, and return new control value</code>

=== Parameters ===

| ''set'' | setpoint / target |
| ''out'' | Initial output value |
| ''direction'' | 1 (normal) or -1 (reverse) |
| ''Kp'' | Proportional component |
| ''Ki'' | Integral response component |
| ''Kd'' | Derivative response component |
| ''min'' | Smallest output value allowed |
| ''max'' | Largest output value allowed |

=== Return value ===

The PID_update function returns the calculated output value.

=== Example usage ===

<code javascript>    

   new p[PID];  // create a PID 

   main() 
   {
      // Initialize the PID with target and no output
      PID_new(p, 50.0, 0.0);
      
      // Limit output to +/- 10
      PID_limits(p, -10.0, 10.0); 
      
      // Set the tuning parameters 
      PID_tune(p, 0.2, 0.04, 0.01);
      
      // Set update speed to 100ms
      SetTickInterval( 100 );
   }
   
   @Tick(uptime) 
   {
      new Float:psi;      
      new Float:v;
      
      // Read and scale a sensor input (0-100psi from 4-20mA sensor)
      psi = 100.0 * ((GetInputValue(1, INVAL_RAW)-4000)/16000);
      
      // Update the PID with the feedback value
      v = PID_update(p, psi);
      
      // Apply to output
      SetOutput(4, fround(v+50));
   }
   
</code>

NOTE: The values used in the above example are not from a real world setup. Please make sure you understand how PID works and how to correctly tune the variables if you use any of the PID functions.