Dicas de como eliminar o repique das chaves mecânicas

O repique (bouncing) das chaves mecânicas é um processo natural do chaveamento. Em circuitos sensíveis ao repique é necessário eliminá-lo utilizando ou circuitos de hardware analógico, ou software, ou hardware digital. Nos sites a seguir o processo é explicado, e são apresentadas algumas soluções.

• Como eliminar o repique das chaves (bouncing).
• Debounce Logic Circuit (with VHDL example)

Códigos VHDL

Código de www.labbookpages.co.uk

library ieee;
use ieee.std_logic_1164.all;
use ieee.numeric_std.all;

entity SwitchDebouncer is
	generic (CLK_FREQ			: positive;
				NUM_SWITCHES	: positive);
	port (	clk				: in	std_logic;
				reset				: in	std_logic;
				switchesIn		: in	std_logic_vector(NUM_SWITCHES-1 downto 0);
				switchesOut		: out	std_logic_vector(NUM_SWITCHES-1 downto 0));
end entity;

architecture Structural of SwitchDebouncer is
	signal sample	: std_logic;
begin

	SampleGen : process(clk)
		constant SAMPLE_COUNT_MAX	: integer := (CLK_FREQ / 2000) - 1;	-- 500 us
		variable counter				: integer range 0 to SAMPLE_COUNT_MAX;
	begin
		if (clk'event and clk='1') then
			if (reset='1') then
				sample	<= '0';
				counter	:= 0;
			else
				if (counter=SAMPLE_COUNT_MAX) then
					counter	:= 0;
					sample	<= '1';
				else
					sample	<= '0';
					counter	:= counter + 1;
				end if;
			end if;
		end if;
	end process;

	DebounceGen : for sw in 0 to NUM_SWITCHES-1 generate
		constant PULSE_COUNT_MAX	: integer := 20;
		signal sync						: std_logic_vector(1 downto 0);
		signal counter					: integer range 0 to PULSE_COUNT_MAX;
	begin
		Debounce : process(clk)
		begin
			if (clk'event and clk='1') then
				if (reset='1') then
					sync					<= (others => '0');
					counter				<= 0;
					switchesOut(sw)	<= '0';
				else
					sync <= sync(0) & switchesIn(sw);
					if (sync(1)='0') then		-- Switch not pressed
						counter <= 0;
						switchesOut(sw) <= '0';

					elsif(sample = '1') then	-- Switch pressed
						if (counter=PULSE_COUNT_MAX) then
							switchesOut(sw) <= '1';
						else
							counter <= counter + 1;
						end if;
					end if;
				end if;
			end if;
		end process;
	end generate;
end Structural;

Código 1 de eewiki.net

Código 2 de eewiki.net