need helps in coding...

hi i'm using an ultrasonic sensor to measure distance which produces PWM output, the pwm output is 147us/inch. i want to implement it in de2 board.

i'm using 50MHz input clock from de2 board and the input from the sensor is 147us/inch. so 147us / 20ns = 7350 counts per inch. i'm already tried to do some coding to read the sensors output, i'm planning to use the sensor to measure distance up to 8 inch. so basically i just count the counter to 7350 to 1 inch and continue counting to 2 inch and so on. this is the coding,am i doing it right or is it violates the way to reads pwm? when i compile it using quartus there are no errors but when i use the sensor nothing happens.. anyone has any suggestion.?

thank you,

regards,

faizul

library IEEE;

use IEEE.STD_LOGIC_1164.ALL;

use IEEE.STD_LOGIC_ARITH.ALL;

use IEEE.STD_LOGIC_UNSIGNED.ALL;

entity maxsonar_pwm_signal_decoder is

Port ( clk : in STD_LOGIC;

reset : in STD_LOGIC;

maxsonar_pwm : in STD_LOGIC;

y : out std_logic_vector(0 to 7);

led : out std_logic;

pwm_distance : out std_logic_vector(2 downto 0));

end maxsonar_pwm_signal_decoder;

architecture Behavioral of maxsonar_pwm_signal_decoder is

signal pwm_inches : std_logic_vector(2 downto 0);

signal pwm_distance_i : std_logic_vector(2 downto 0);

begin

pwm_distance <= pwm_distance_i;

process(clk)

variable pwm_count : integer range 0 to 60000;

begin

if reset = '1' then

pwm_count := 0;

pwm_distance_i <= "000";

elsif rising_edge(clk) then

if maxsonar_pwm = '1' then

if pwm_count = 7350 then

pwm_inches <= "001";

end if;

if pwm_count = 14700 then

pwm_inches <= "010";

end if;

if pwm_count = 22050 then

pwm_inches <= "011";

end if;

if pwm_count = 29400 then

pwm_inches <= "100";

end if;

if pwm_count = 36750 then

pwm_inches <= "101";

end if;

if pwm_count = 44100 then

pwm_inches <= "110";

end if;

if pwm_count = 51450 then

pwm_inches <= "111";

else

pwm_count := pwm_count + 1;

end if;

else

if (pwm_inches > "000") then

pwm_distance_i <= pwm_inches;

end if;

pwm_count := 0;

pwm_inches <= "000";

end if;

end if;

end process;

process(pwm_inches )

begin

case pwm_inches is

when "000"=>

y<="10000000";

when "001"=>

y<="01000000";

when "010"=>

y<="00100000";

when "011"=>

y<="00010000";

when "100"=>

y<="00001000";

when "101"=>

y<="00000100";

when "110"=>

y<="10000010";

when "111"=>

y<="00000001";

when others=>

y<="00000000";

led <= '1';

end case;

end process;

end Behavioral;