Hi! Does anyone know if it's possible to generate at least 10 kGz sinewave with msp430 TimerB PWM mode? With 8bit resolution? Thanks Andrew
Sinewave
Started by ●October 10, 2002
Reply by ●October 11, 20022002-10-11
Hi Andrew, It would depend on how "clean" you would want your sine. With most 8/16 bit MCUs howvere you will never make 10 kHz sinewave directly - neither with PWM or directly with a DAC. Some basic maths : for 8 bit resolution your PWM would be MCU clock / 256 it its best. So : say 8 MHz max on MSP430 : 8 MHz / 256 = 31.25 kHz PWM. To generate a sine wave directly, the most efficient would be to use a "phase accumulator" look-up table, but it depends on how accurately you want to be able to set your sine frequency (if you need that at all) With a 31.25 kHz PWM I wouldn't see a technique generating an acceptable sinewave at a freq much higher than say 0.5 kHz or so. You could of course obey the Nyquist limit (2 times sample rate) and output a square wave at 20 kHz, and then filter it heavily to recover the "fundamental 10 kHz" sine wave. But you would need very heavy analog filtering then. > Hi! > > Does anyone know if it's possible to generate at least 10 kGz sinewave with > msp430 TimerB PWM mode? With 8bit resolution? > > Thanks > Andrew > > > > . > > > > ">http://docs.yahoo.com/info/terms/ > >
Reply by ●October 11, 20022002-10-11
Hi!
> Hi Andrew,
>
> It would depend on how "clean" you would want your sine.
> With most 8/16 bit MCUs howvere you will never make 10 kHz sinewave
> directly -
> neither with PWM or directly with a DAC.
>
> Some basic maths :
>
> for 8 bit resolution your PWM would be MCU clock / 256 it its best.
> So :
> say 8 MHz max on MSP430 :
> 8 MHz / 256 = 31.25 kHz PWM.
[..]
Thanks Kris! Now I understand.
But now I can make my question more precise - I have to generate different
sounds, from 0 to 2 kHz, with different volumes. Volume need to have at
least 64 gradations. And now I'm totally confused. May be you have any
ideas? May be I'm trying to go in wrong direction and it needs some other
external solutions?
Thanks
Andrew
Reply by ●October 11, 20022002-10-11
>From: "Andrew Doilidov" <andrew@andr...> >Reply-To: msp430@msp4... >To: <msp430@msp4...> >Subject: Re: [msp430] Sinewave >Date: Fri, 11 Oct 2002 09:56:30 -0400 > >Hi! > > > Hi Andrew, > > > > It would depend on how "clean" you would want your sine. > > With most 8/16 bit MCUs howvere you will never make 10 kHz sinewave > > directly - > > neither with PWM or directly with a DAC. > > > > Some basic maths : > > > > for 8 bit resolution your PWM would be MCU clock / 256 it its best. > > So : > > say 8 MHz max on MSP430 : > > 8 MHz / 256 = 31.25 kHz PWM. >[..] > >Thanks Kris! Now I understand. >But now I can make my question more precise - I have to generate different >sounds, from 0 to 2 kHz, with different volumes. Volume need to have at >least 64 gradations. And now I'm totally confused. May be you have any >ideas? May be I'm trying to go in wrong direction and it needs some other >external solutions? A software DDS might be the way to go. Look at this web site: http://www.myplace.nu/avr/minidds/ The output voltage is fixed. You could vary it by scaling the samples before they are sent to the DAC. I've got an improved version of Jesper's Mini DDS here: http://webspace.webring.com/people/jl/leon_heller//minidds.html Leon -- Leon Heller, G1HSM Tel: +44 1424 14790 Email:leon_heller@leon... My web page: http://webspace.webring.com/people/jl/leon_heller/ My low-cost Altera Flex design kit: http://www.leonheller.com _________________________________________________________________ MSN Photos is the easiest way to share and print your photos: http://photos.msn.com/support/worldwide.aspx
Reply by ●October 11, 20022002-10-11
Hi Leon, Thanks for the tip about the SW DDS. I wasn't aware a phase accu setup can achieve such high frequencies on a low Mips MCU.... Well, you learn something everyday.... ! I'll have to check it one day, to see how long it takes to change freqs. in the "SW DDS". B rgds Kris ----- Original Message ----- From: Leon Heller To: msp430@msp4... Sent: Saturday, October 12, 2002 3:25 AM Subject: Re: [msp430] Sinewave >From: "Andrew Doilidov" <andrew@andr...> >Reply-To: msp430@msp4... >To: <msp430@msp4...> >Subject: Re: [msp430] Sinewave >Date: Fri, 11 Oct 2002 09:56:30 -0400 > >Hi! > > > Hi Andrew, > > > > It would depend on how "clean" you would want your sine. > > With most 8/16 bit MCUs howvere you will never make 10 kHz sinewave > > directly - > > neither with PWM or directly with a DAC. > > > > Some basic maths : > > > > for 8 bit resolution your PWM would be MCU clock / 256 it its best. > > So : > > say 8 MHz max on MSP430 : > > 8 MHz / 256 = 31.25 kHz PWM. >[..] > >Thanks Kris! Now I understand. >But now I can make my question more precise - I have to generate different >sounds, from 0 to 2 kHz, with different volumes. Volume need to have at >least 64 gradations. And now I'm totally confused. May be you have any >ideas? May be I'm trying to go in wrong direction and it needs some other >external solutions? A software DDS might be the way to go. Look at this web site: http://www.myplace.nu/avr/minidds/ The output voltage is fixed. You could vary it by scaling the samples before they are sent to the DAC. I've got an improved version of Jesper's Mini DDS here: http://webspace.webring.com/people/jl/leon_heller//minidds.html Leon -- Leon Heller, G1HSM Tel: +44 1424 14790 Email:leon_heller@leon... My web page: http://webspace.webring.com/people/jl/leon_heller/ My low-cost Altera Flex design kit: http://www.leonheller.com _________________________________________________________________ MSN Photos is the easiest way to share and print your photos: http://photos.msn.com/support/worldwide.aspx .
Reply by ●October 12, 20022002-10-12
----- Original Message ----- From: "Kris De Vos" <microbit@micr...> To: <msp430@msp4...> Sent: Friday, October 11, 2002 9:53 PM Subject: Re: [msp430] Sinewave > Hi Leon, > > Thanks for the tip about the SW DDS. > I wasn't aware a phase accu setup can achieve such high frequencies on a low Mips MCU.... > Well, you learn something everyday.... ! It is running at 11 MIPS. > > I'll have to check it one day, to see how long it takes to change freqs. in the "SW DDS". Could work it out. It's restricted by the comms speed. The DDS itself should change in a few ns. Regards, Leon -- Leon Heller, G1HSM leon_heller@leon... http://webspace.webring.com/people/jl/leon_heller/
Reply by ●October 17, 20022002-10-17
--- In msp430@y..., "Andrew Doilidov" <andrew@u...> wrote: > Hi! > > Does anyone know if it's possible to generate at least 10 kGz sinewave with > msp430 TimerB PWM mode? With 8bit resolution? > > Thanks > Andrew Program a UART channel to 19.K baud (you only need the transmit pin), then continuously issue 0x55 out of TXD, which produces a square wave at 9600 Hz. Then RC filter it so you only get the fundamental, which is a sinewave at 9600. It will not be 100% pure for a simple filter, but it's cheap, simple, and requires very little micocontroller bandwidth. Oscar
