Hello, I am working on a senior design project and have a DE2 board connected to external circuitry. There are pushbuttons on the external circuit which control leds also on that circuit board. My design requires that I press the pushbutton and the led lights up and I press it a second time and the led goes off. It turns out that those pushbuttons which are single-pole-double-throw (SPDT) are not debounced and give multiple outputs when I want a clean signal. I would like to know if there is a reference design so I can build debounced circuitry for the buttons in Quartus. If not, how do I build debouncers in Quartus for SPDT pushbuttons? Thanks. Kofi.

Normally there are delayed timer double check circuit and state machine circuit used as debouncer. You will find spending a while on google.

Actually, I believe DE2 switches are debounced with a 74HC245. You should not see multiple inputs for a single button depression. Remember that the switches (or 'key's) are active high. When you push the button it will be low for the period of time that you have it depressed (which even if you push it very quickly will be many thousands of clock cycles). But you will not see it oscillate between a one and a zero after it is depressed (you can prove this to yourself by building a simple SignalTap file and analyzing the operation in hardware). In order to ensure your circuit operates appropriately I would suggest that you watch for the switch (or key) to go from a low to a high (the switches are a logic 1 when not depressed). This will ensure that a single button press results in your code executing only once. If you post your code snippet, then I will have a look...

Hi, I'm actually using pushbuttons on an external circuit and not the pushbuttons on the DE2. I'm going to build debounced circuitry in Quartus to fix it. Thanks for the reply.

Kofinator, Please post your reference design when you're done if you don't mind sharing.

am working on a design project and have a DE2-70 board.I want to control on board LEDS from my PC. How can I make dialogue based application using NIOS II IDE.

DE2 Quartus debounced circuit | Altera Community

15 Replies

Altera_Forum
Honored Contributor
14 years ago
Hello,
I made a simplest program for hex counter it supposed to count push-button clicks.
It present the result on a single 7seg display and 4 LEDs, unfortunately I've got a bouncing problem.
I'm using a Altera Cyclone II BAIXUN ASK2CB dev. board it has on board push-button
Can you please suggest how can i debounce it, so the bits go one by one?

Here is my code:
========================================
library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.STD_LOGIC_ARITH.ALL;
use IEEE.STD_LOGIC_UNSIGNED.ALL;

entity test is
port (Y : out std_logic_vector (6 downto 0); -- 7 seg digit
B : out std_logic;
pb : in std_logic;
count : out std_logic_vector(3 downto 0);
reset :in std_logic
);
end entity test;

architecture Behavioral of test is
signal c: std_logic_vector(3 downto 0) :=(others => '0'); --initializing count to zero.
begin
counting: process(pb,reset) is
begin
if rising_edge (pb) then
if(c = "1111") then -- when count reaches its maximum(that is 15) reset it to 0
c <="0000";
end if;
c <= c+'1'; --increment count at every positive edge of clk.
end if;
if(reset='0') then --when reset equal to '0' make count equal to 0.
c <=(others => '0'); -- c ="0000"
end if;

case c is
when "0000"=>Y<="1000000";-- 0
when "0001"=>Y<="1111001";-- 1
when "0010"=>Y<="0100100";-- 2
when "0011"=>Y<="0110000";-- 3
when "0100"=>Y<="0011001";-- 4
when "0101"=>Y<="0010010";-- 5
when "0110"=>Y<="0000010";-- 6
when "0111"=>Y<="1111000";-- 7
when "1000"=>Y<="0000000";-- 8
when "1001"=>Y<="0010000";-- 9
when "1010"=>Y<="0001000";-- A
when "1011"=>Y<="0000011";-- b
when "1100"=>Y<="1000110";-- C
when "1101"=>Y<="0100001";-- d
when "1110"=>Y<="0000110";-- E
when "1111"=>Y<="0001110";-- F
when others=>Y<="1111111";-- in other cases balnk
end case;
end process counting;
B<='0';
count<=c;
end architecture Behavioral;
==========================================
Altera_Forum
Honored Contributor
14 years ago
you shouldn't use the push button as clock input, it isvery unreliable and sensitive to bounces, as you discovered.
Instead, use a regular clock (I'm sure the board has an oscillator you can use) and monitor the pb signal on each clock cycle. You can detect a change on the button status by comparing the current value of pb with the previous one. You will also probably need to implement a delay for proper debouncing.
Altera_Forum
Honored Contributor
14 years ago
Thank you Daixiwen!

I see, anyway i tried to make a delay but nothing seem to work yet, still trying.
I'm a beginner, so i'll will be really glad if you can help me with solving upon my code,
to understand it better! If its not to much to ask!
Altera_Forum
Honored Contributor
14 years ago
How did you implement the delai? I can for example have a counter increasing from the last time you detected a rising edge, ad you don't take into account a new rising edge before this counter reaches a predetermined value.
Altera_Forum
Honored Contributor
13 years ago
Hi Daixiwen and thanks,

Sorry for a long time no answer. Finally solved the problem. using the following code:

library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_unsigned.all;

entity debounce is
generic(
counter_size : INTEGER := 19); --counter size (19 bits gives 10.5ms with 50MHz clock)
port(
Digit : out std_logic_vector (6 downto 0); -- 7 seg digit
hex_count : out std_logic_vector(3 downto 0); -- Hexadecimal result
clk, reset, button : in std_logic; --input signals
Digit_en : out std_logic); -- 7 seg digit enable
end debounce;

architecture logic of debounce is
signal counter : std_logic_vector(3 downto 0) :=(others => '0'); --initializing count to zero.
signal flipflops : std_logic_vector(1 downto 0); --input flip flops
signal counter_out : std_logic_vector(counter_size downto 0) := (others => '0'); --counter output
signal counter_set : std_logic; --sync reset to zero
signal result : std_logic; --debouncer result
begin

counter_set <= flipflops(0) xor flipflops(1); --determine when to start/reset counter

process(clk)
begin
if(clk'event and clk = '1') then
flipflops(0) <= button;
flipflops(1) <= flipflops(0);
if(counter_set = '1') then --reset counter because input is changing
counter_out <= (others => '0');
elsif(counter_out(counter_size) = '0') then --stable input time is not yet met
counter_out <= counter_out + 1;
else --stable input time is met
result <= not flipflops(1);
end if;
end if;
end process;

process(result)
begin
if(reset='0') then --when reset equal to '0' make count equal to 0.
counter <=(others => '0'); -- c ="0000"
elsif(result'event and result = '1') then
if(counter = "1111") then -- when count reaches its maximum(that is 15) reset it to 0
counter <="0000";
end if;
counter <= counter+'1'; --increment count at every positive edge of clk.
end if;
case counter is
when "0000"=>Digit<="1000000";-- 0
when "0001"=>Digit<="1111001";-- 1
when "0010"=>Digit<="0100100";-- 2
when "0011"=>Digit<="0110000";-- 3
when "0100"=>Digit<="0011001";-- 4
when "0101"=>Digit<="0010010";-- 5
when "0110"=>Digit<="0000010";-- 6
when "0111"=>Digit<="1111000";-- 7
when "1000"=>Digit<="0000000";-- 8
when "1001"=>Digit<="0010000";-- 9
when "1010"=>Digit<="0001000";-- A
when "1011"=>Digit<="0000011";-- b
when "1100"=>Digit<="1000110";-- C
when "1101"=>Digit<="0100001";-- d
when "1110"=>Digit<="0000110";-- E
when "1111"=>Digit<="0001110";-- F
when others=>Digit<="1111111";-- in other cases balnk
end case;
end process;
Digit_en<='0';
hex_count<=counter;
end;

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DE2 Quartus debounced circuit

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