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Altera_Forum
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8 years ago

VHDL Code For Ultrasonic Distance Sensor HC-SR04

I am trying to write the VHDL code for it but it is not working, it shows always 00 ( cm1 = 0 and cm0 = 0). Can you pleaseee help me? Do you detect any problem in the code:

Summation of how the sensor works: you send 10 us trigger to the sensor and then wait for the echo signal from it. The width of the echo determines the distance. In 5800 clk cycles of echo you measure 1 cm( with 100 MHZ clk of BASYS 3). Here is the code: 

library IEEE;
    use IEEE.STD_LOGIC_1164.ALL;
    use IEEE.NUMERIC_STD.ALL;
    entity sonar is
        Port ( clk : in STD_LOGIC;
               trig : out STD_LOGIC;--trigger
               echo : in STD_LOGIC;
               cm1 : out unsigned(3 downto 0); --most significant bit of distance in binary form
               cm0 : out unsigned(3 downto 0));
    end sonar;
    architecture sonar_arch of sonar is
    signal count: integer range 0 to 5800; -- I will only measure up to 100 cm
    signal tmpcm1: unsigned(3 downto 0) := "0000"; --most significant bit of ditance
    signal tmpcm0: unsigned(3 downto 0) := "0000";
    signal sendTrig: std_logic := '1';
    begin
        process(clk)
        begin
            if rising_edge(clk) then
                if sendTrig = '1' then -- send 10us trig
                    if count = 10000 then -- 10 us trig is completed, reset tmp signals for the new calculation
                        trig <= '0';
                        sendTrig <= '0';
                        count <= 0;
                        tmpcm0 <= "0000";
                        tmpcm1 <= "0000";
                    else
                        trig <= '1';
                        count <= count + 1;
                    end if; 
                else -- stop sending trig, do the calculation (5800 clk cycle = 1cm)(count enters here as 0)
                    if echo = '1' then -- we can start calculating the width of the echo
                        if count = 5799 then--we measuered 1 cm
                            if tmpcm0 = "1001" then
                                if tmpcm1 = "1001" then
                                    sendTrig <= '1';--max distance to be measured(100 cm), stop measuring, re-send the trig(also update the output)
                                    cm0 <= tmpcm0;
                                    cm1 <= tmpcm1;
                                else
                                    tmpcm1 <= tmpcm1 + "0001";
                                    tmpcm0 <= "0000";
                                end if;
                            else
                                tmpcm0 <= tmpcm0 + "0001";
                            end if;
                            count <= 0;
                        else
                            count <= count + 1;
                        end if;
                        if echo = '0' then --equivalent of if falling_edge(echo), distance is measured, send another trig(also update te output)
                            sendTrig <= '1';
                            cm0 <= tmpcm0;
                            cm1 <= tmpcm1;                      
                        end if;                                       
                    end if;                        
                end if;
            end if;      
        end process;
     
end sonar_arch;

3 Replies

  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    8 years ago

    Well, for a start, you have the following structure: 

    
if echo = '1' then
  if echo  = '0' then
    --this is impossible, as echo cannot be '1' and '0' at the same time

    This case will never occur.

    If you have a "working" simulation, but it's not working in hardware, then I suggest there is something wrong with how you're testing your code. Maybe you misunderstood how the echo works? or how some other interface should work?
  • Altera_Forum's avatar
    Altera_Forum
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    8 years ago

    Yes I realized that mistake. I edited my code accordingly this way, but it still does not work. It either shows 99 or 00 after each reprograming the FPGA. Also I don't know how to write the testbench:( I would appreciate if you write it for me( I believe it is quite easy for a given code, otherwise I wouldn't ask such a thing.). The new code is: 

    library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.NUMERIC_STD.ALL;
entity sonar is
    Port ( clk : in STD_LOGIC;
           trig : out STD_LOGIC;--trigger
           echo : in STD_LOGIC;
           cm1 : out unsigned(3 downto 0); --most significant bit of distance in binary form
           cm0 : out unsigned(3 downto 0));
end sonar;
architecture sonar_arch of sonar is
begin
    process(clk)
    variable count: integer range 0 to 10000;
    variable tmpcm1: unsigned(3 downto 0) := "0000";
    variable tmpcm0 : unsigned(3 downto 0) := "0000";
    variable sendTrig: std_logic := '1';
    variable echoPrev: std_logic:= '0';
    variable echoCurrent : std_logic:= '0';
    begin
        if rising_edge(clk) then
            if sendTrig = '1' then -- send 10us trig
                if count = 1000 then -- 10 us trig is completed, reset tmp signals for the new calculation
                    trig <= '0';
                    sendTrig := '0';
                    count := 0;
                    tmpcm0 := "0000";
                    tmpcm1 := "0000";
                else
                    trig <= '1';
                    count := count + 1;
                end if; 
            else -- stop sending trig, do the calculation (5800 clk cycle = 1cm)(count enters here as 0)
                if echo = '1' then -- we can start calculating the width of the echo
                    if count = 5799 then--we measuered 1 cm
                        if tmpcm0 = "1001" then
                            if tmpcm1 = "1001" then
                                sendTrig := '1';--max distance to be measured(100 cm), stop measuring, re-send the trig(also update the output)
                                cm0 <= tmpcm0;
                                cm1 <= tmpcm1;
                            else
                                tmpcm1 := tmpcm1 + "0001";
                                tmpcm0 := "0000";
                            end if;
                        else
                            tmpcm0 := tmpcm0 + "0001";
                        end if;
                        count := 0;
                    else
                        count := count + 1;
                    end if;
                    if echoPrev = '1' and echoCurrent = '0' then --falling edge of echo, edit the output, start sending new trigger
                        sendTrig := '1';
                        cm0 <= tmpcm0;
                        cm1 <= tmpcm1;
                    end if;                              
                end if;                        
            end if;
            echoPrev := echoCurrent;
            echoCurrent := echo;
        end if;      
    end process;
     
end sonar_arch;
  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    8 years ago

    There are many tutorials on the internet on how to write a testbench.

    I suggest having a go yourself, and coming back here with any issues you are having.

    One thing I would recommend is that you do not use variables. Use all signals