Q:

VHDL How to switch output from 1 to 0 after a period of time? 

entity seguidor is
    port(
        clk, sensorIzq, sensorDer, sensorDisp : in std_logic;
        llantaIzq, llantaDer, disp: out std_logic);
end;

architecture comportamiento of seguidor is

begin

    movimiento: process (sensorIzq, sensorDer, sensorDisp,clk)
     begin
        if(sensorIzq='1' and sensorDer='0' and sensorDisp = '0') then
            llantaIzq<='1';
            llantaDer<='0';
        elsif(sensorIzq='0' and sensorDer='1'and sensorDisp = '0') then
            llantaIzq<='0';
            llantaDer<='1';
        elsif(sensorIzq = '1' and sensorDer = '1' and sensorDisp = '0') then
            llantaIzq <= '1';
            llantaDer <= '1';
        elsif(sensorIzq = '1' and sensorDer = '1' and sensorDisp = '1') then
            llantaIzq <= '0';
            llantaDer <= '0';

        end if;
    end process movimiento;
    end comportamiento;

So, the code is for a line follower, if it reads a '1' from one of the sensors it should pass a '1' (i.e 5v.)  to one of its wheels.  After reading a '1' from "sensorDisp", the car should stop for a little while, giving "disp" a value of '1' in this while.  After that, it should continue on its merry way.  I'm having a hard time trying to achieve this delay.  Thanks for the help! 

A:

I have done similar thing on Atlys. 
Have clk counters. Know the frequency of the clock in .ucf file ( mapping file ). 
Have a boolean for waiting state, isWait .When sensorDisp is 1 then isWait = true 
I have mentioned pseudo code below. 
You can create a separate process for this with input clk and sensordisp. 
And remember if any variable/signal isn't assigned any value in any run of the code, if will infer a latch as it needs the previous value as it isn't assigned. 
movimiento: process (clk,sensorIzq, sensorDer, sensorDisp,clk)
     begin
     if(clk edge ) then 
        if (isWait) then 
            if(wait_counter < "frequency")) then 
              wait_couter++;
             else 
              isWait = False;
              Disp = '0';
            end if;
        else 
          if(sensorDisp = '1') then 
             wait_counter = 0;
             isWait = True;
              Disp <= '1';
          end if;

          if(sensorIzq='1' and sensorDer='0' and sensorDisp = '0') then
              llantaIzq<='1';
              llantaDer<='0';
          elsif(sensorIzq='0' and sensorDer='1'and sensorDisp = '0') then
              llantaIzq<='0';
              llantaDer<='1';
          elsif(sensorIzq = '1' and sensorDer = '1' and sensorDisp = '0') then
              llantaIzq <= '1';
              llantaDer <= '1';
          elsif(sensorIzq = '1' and sensorDer = '1' and sensorDisp = '1') then
              llantaIzq <= '0';
              llantaDer <= '0';
          end if;
      end if;
    end if;
    end process movimiento;
    end comportamiento;

