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Newbie
Newbie
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Registered: ‎05-19-2014

PMOD AMP1 Troubleshooting

I've recently purchsaed the PMOD AMP1 module from digilent for use with my Nexys 2.

 

When I program the demo project (http://www.digilentinc.com/Data/Products/PMOD-AMP1/PmodAMP1_ISE_Demo.zip)

on the headphone output I can barely hear an extremely high pitch tone on the headphone out.

 

After reading through the source I realised this project is setup for a 100Mhz clock while my board is 50M. I modified the synth.vhd as below:

 

entity synth is
	port(clk : in std_logic;
		  syn_out : inout std_logic_vector(7 downto 0));
end synth;

architecture Behavioral of synth is

signal sclk : std_logic_vector(10 downto 0);
	
begin
	process(clk)
		begin 
			if clk'event and clk = '1' then
			-- divide a clock by "10111010101" (1493) which is about the value of 100M/256/261.6
			-- where 100M is the clock frequency on a Nexys3
			-- 256 is the number of points in the sine wave table
			-- 261.6 is the frequency of a middle C
				if sclk = "1011101010" then -- MODIFIED decreased by half for 50Mhz clk (746 is new clock divider)
					--"11111111" is 255 is the maximum point in the sine wave table
					if syn_out < "11111111" then 
						syn_out <= syn_out + 1;
					else
						syn_out <= "00000000";
					end if;
					sclk <= "00000000000";
				else
					sclk <= sclk + 1;
				end if;
			end if;
	end process;

end Behavioral;

 And re-programmed however this made absolutely no difference to the faint high pitched tone .

 

I've tried through speakers incase it was a gain issue, but to no avail. Also adjusting the pot on the PMOD itself.

 

Just wondering if anyone else has had any experience with this module/board combination?

 

Unfortunately I don't have access to an oscilliscope so can't see if the intermediate PWN signal is being correctly generated.

 

I also have the PMOD DA2 but thought I'd start with this as before jumping into the deep(er) end.

 

Regards,

Lawrence

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Highlighted
Newbie
Newbie
7,407 Views
Registered: ‎05-19-2014

Probably worth mentioning I've also replaced the UCF file with the Nexys 2 one and uncommented the relevent nets (CLK, JA<3 - 0>

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