Forums

Generate DTMF

Started by cell April 28, 2008
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!
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!
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

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