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Date: | Tue, 31 Dec 2013 13:59:11 -0600 |
Message-ID: | <CAM4zO3pAfPZ5aSWwwaykcXtB=Ruyxme8a1ZSGb46XLQfFY-FCw@mail.gmail.com> |
Subject: | Re: [geda-user] Help sending a sine wave to a speaker |
From: | Ozzy Lash <ozzy DOT lash AT gmail DOT com> |
To: | geda-user AT delorie DOT com |
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--047d7bfd05fc77099f04eed9fe40 Content-Type: text/plain; charset=ISO-8859-1 On Tue, Dec 31, 2013 at 1:26 PM, Rob Butts <r DOT butts2 AT gmail DOT com> wrote: > It has been a while since I've written major C code so I'm having a hard > time coming up with the code. > I have a simple design where I use a microchip pic16f1825 to read a byte > from an eeprom via spi and send it to a dac and ultimately to a speaker. > As a dac and speaker test I want to send a simple 1000Hz sine wave to the > dac at an 8KHz rate. > > Can anyone check my thoughts below? Here's my thinking... > If I set my timer to interrupt at an 8KHz rate and if I want to play the > tone for 10 seconds the for loop might look something like this: > > for(j=0; j < 80000; j++){ > // j is the sample index > // straight sine function means one cycle per 2*pi samples > // sample(j) = sin(j) > // multiply by 2*pi now it is one cycle per sample > // sample(j) = sin((2 * pi) * j) > // multiply by 1,000 samples per second now it is cycles per second > // sample(j) = sin(1000 * 2 * pi * j) > // divide by 8000 samples per second now it is cycles per 8000 samples > // sample(j) = sin(1000 * 2 * pi * j / 8000) > // the 1000 cycles is the frequency so in those terms > // sample(j) = sin(freq * 2 * pi * j / 8000) > // now if I want to normalize the amplitude to 0xff the final value > is > // sample(j) = 0xff * sin(freq * 2 * pi * j / 8000) > // so... declaring sample as a float > sample = 0xff * sin(freq * 2 * pi * j / 8000); > while(!update_dac){ // where update_dac is set to 1 in the timer > interrupt handler > } > update_ dac = 0; > send_dac((UINT8) sample); > } > > When I execute the code and step through it the value for sample when j = > 1 is 180.238where I expect 3.146 > > Can someone see my error or what is going on? > > Thanks > If freq=1000 and j=1, then sample is 255*sin(pi/4). sin(pi/4)=sqrt(2)/2, so sample should be about 180 Did you do the sin on a calculator and have it in degrees mode instead of radians? Bill --047d7bfd05fc77099f04eed9fe40 Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable <div dir=3D"ltr"><div class=3D"gmail_extra"><div class=3D"gmail_quote">On T= ue, Dec 31, 2013 at 1:26 PM, Rob Butts <span dir=3D"ltr"><<a href=3D"mai= lto:r DOT butts2 AT gmail DOT com" target=3D"_blank">r DOT butts2 AT gmail DOT com</a>></span>= wrote:<br> <blockquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border-left:1p= x #ccc solid;padding-left:1ex"><div dir=3D"ltr"><div>It has been a while si= nce I've written major C code so I'm having a hard time=20 coming up with the code. <br></div><div>I have a simple design where I use = a microchip=A0pic16f1825 to=20 read a byte from an eeprom via spi and send it to a dac and ultimately to a= =20 speaker.=A0 As a dac and speaker test I want to send a simple 1000Hz sine w= ave to=20 the dac at an 8KHz rate.=A0<br>=A0=A0=A0 <br>Can anyone=A0check my thoughts= below?=A0 Here's my thinking... <br>If I=20 set my timer to interrupt at an 8KHz rate and if I want to play the tone fo= r 10=20 seconds the for loop might look something like this: <br>=A0 <br>for(j=3D0;= =A0j <=20 80000; j++){ <br>=A0=A0=A0=A0 //=A0j is the sample index <br>=A0=A0=A0 // s= traight sine function=20 means one cycle per 2*pi samples <br>=A0=A0=A0 //=A0sample(j) =3D sin(j) <b= r>=A0=A0=A0 //=20 multiply by 2*pi now it is one cycle per sample <br>=A0=A0=A0 // sample(j) = =3D sin((2 *=20 pi) * j) <br>=A0=A0=A0 // multiply by 1,000 samples per second now it is cy= cles per=20 second <br>=A0=A0=A0 // sample(j) =3D sin(1000 * 2 * pi * j) <br>=A0=A0=A0 = // divide by 8000=20 samples per second now it is cycles per 8000 samples <br>=A0=A0=A0 // sampl= e(j) =3D=20 sin(1000 * 2 * pi * j / 8000) <br>=A0=A0=A0 // the 1000 cycles is the frequ= ency so in=20 those terms <br>=A0=A0=A0 //=A0 sample(j) =3D sin(freq * 2 * pi * j / 8000)= <br>=A0=A0=A0 // now=20 if I want to normalize the amplitude to 0xff=A0 the final value is <br>=A0= =A0=A0 //=20 sample(j) =3D 0xff * sin(freq * 2 * pi * j / 8000) <br>=A0=A0=A0 // so...= =A0=A0=A0=A0declaring=20 sample as a float <br>=A0=A0=A0 sample =3D 0xff * sin(freq * 2 * pi * j / 8= 000); <br>=A0=A0=A0=20 while(!update_dac){=A0=A0=A0 // where update_dac is set to 1 in the timer i= nterrupt=20 handler <br>=A0=A0=A0 } <br>=A0=A0=A0 update_ dac =3D 0; <br>=A0=A0=A0 send= _dac((UINT8) sample);=20 <br>}=A0<br>=A0 <br>When I execute the code and step through it the value f= or sample=A0when j =3D 1 is 180.238where I expect 3.146</div><div>=A0</div>= <div>Can someone see my error or what is going on?</div><div>=A0</div><div>= Thanks</div> </div> </blockquote></div><br></div><div class=3D"gmail_extra">If freq=3D1000 and = j=3D1, then sample is 255*sin(pi/4).=A0 sin(pi/4)=3Dsqrt(2)/2, so sample sh= ould be about 180<br><br></div><div class=3D"gmail_extra">Did you do the si= n on a calculator and have it in degrees mode instead of radians?<br> <br></div><div class=3D"gmail_extra">Bill<br></div></div> --047d7bfd05fc77099f04eed9fe40--
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