cell wrote:

> I used a 8052 MCU (24MHz crystal) and a 8 bits R-2R DAC to generate
> DTMF tones.The sampling frequency is 5kHz. The output is then input to
> a 2nd order LP filter. The telephone line seems to not recognize my
> tone. Is the order of filter enough or not?

Apparently there is a bug in your generator. There is absolutely no 
necessity to generate nice and clean DTMF waves other then for the 
regulatory compliance.

Vladimir Vassilevsky
DSP and Mixed Signal Design Consultant
http://www.abvolt.com

On Mon, 28 Apr 2008 19:23:12 -0700, cell wrote:

> I used a 8052 MCU (24MHz crystal) and a 8 bits R-2R DAC to generate DTMF
> tones.The sampling frequency is 5kHz. The output is then input to a 2nd
> order LP filter. The telephone line seems to not recognize my tone. Is
> the order of filter enough or not?
> 
> Thanks!

I'm going to paint my house a greeny-blue color.  How much paint do I 
need to buy?

Or in other words, tell us enough to answer your question, and maybe 
someone will be able to help.

I would expect that nice sine waves fed to an 8-bit DAC with a sufficient 
sampling rate is more than good enough.  Have you looked at your 
telephone line on an oscilloscope and compared your DTMF tones to what 
comes out of a regular telephone?

-- 
Tim Wescott
Control systems and communications consulting
http://www.wescottdesign.com

Need to learn how to apply control theory in your embedded system?
"Applied Control Theory for Embedded Systems" by Tim Wescott
Elsevier/Newnes, http://www.wescottdesign.com/actfes/actfes.html

imaginabale cause

frequency  error
frequency  compages error
signal level oversize or lesssize of your output
The sampling frequency up to 10kHz


"cell" <cellterry@gmail.com> 
??????:9d94bcfe-6efb-42bc-803d-dc7ee7034e14@w1g2000prd.googlegroups.com...
>I used a 8052 MCU (24MHz crystal) and a 8 bits R-2R DAC to generate
> DTMF tones.The sampling frequency is 5kHz. The output is then input to
> a 2nd order LP filter. The telephone line seems to not recognize my
> tone. Is the order of filter enough or not?
>
> Thanks! 

I used a 8052 MCU (24MHz crystal) and a 8 bits R-2R DAC to generate
DTMF tones.The sampling frequency is 5kHz. The output is then input to
a 2nd order LP filter. The telephone line seems to not recognize my
tone. Is the order of filter enough or not?

Thanks!