distance measuring by encoder

Is yours a single or dual phase encoder?

Usually encoders have two phases, namely two square pulses signals 90 degrees out of phase. This allows you to know direction, besides distance.

If this is your case, you may use a standard encoder counter: try browsing opencores.org, search for quadrature encoder/decoder.

Instead, if you have a single phase encoder, you simply need to count raw pulses.

i have one phase encoder ...

i wrote this program but got an errore about the multiplication, how can i alternate that by synthessisable way ??

library IEEE;

use IEEE.std_logic_1164.all;

use ieee.std_logic_arith.all;

use ieee.std_logic_unsigned.all;

entity encoder is

port(

CLK : in std_logic;

sig : in std_logic ;

reset : in std_logic;

req_dist: buffer std_logic_vector(8 downto 0) -- till 5 meter.

);

end entity encoder;

architecture arc_encoder of encoder is

signal tmp_sig : std_logic;

signal counter : std_logic_vector(8 downto 0);

signal distance : std_logic_vector(8 downto 0);

begin

process(CLK)

begin

if (reset='1') then

counter <= (others => '0');

else

distance <= req_dist*24 and "111000000"; ------------------------------------------------------ HERE IS THE ERRORE

end if;

if rising_edge(sig) then

if (counter < distance) then

counter <= counter+1;

else counter <= counter;

end if;

end if;

end process;

end architecture arc_encoder;

Rather than using

if rising_edge(sig)

I'd follow Tricky's advice and make everything synchronous to clk.

Then, sample sig at regular intervals, store in a register and wait for a low to high transition in order to increment counter.

This would also allow you some filtering to avoid fake counts, which is a common problem with single phase encoders, especially if the rotating wheel is supposed to start and stop.