[VoIP] MF tone generator

[Donald Froula]

Sorry, should have sent attachments. Here's all the
stuff.

Don

--- john jones <jjones3601 at yahoo.com> wrote:

> Donald,
> 
> I'd be very interested in seeing the code if it is
> in some high level language.
> 
> Thanks!
> 
> John
> 
> ----- Original Message ----
> From: Donald Froula <dfroula at sbcglobal.net>
> To: voip at ckts.info
> Sent: Friday, June 15, 2007 6:59:50 PM
> Subject: [VoIP] MF tone generator
> 
> I thought there might be some interest in a "Blue
> Box"
> circuit I designed using a 68HC705C8
> microcontroller.
> I have the schematic and S-records for programming
> the
> chip (or I'd be happy to program a blank one).
> 
> It might be useful for getting a toll test board
> running or other applications.
> 
> Don
> 
> Design Notes
> ============
> 
> The microprocessor runs at 4 MHz.
> 
> It is powered directly from three 1.5 V mercury
> button
> cells in series. Current draw at nominal
> volume is only 12 ma (idle) to 17 ma (tone being
> generated).
> 
> One of the 8-bit 68HC705C8 ports is wired to an R-2R
> resistive network made with precision 10K/20K
> resistors. The output of the network (input to the
> LM386N audio amp) is the sum of the
> binary-weighted output of the port (0xFF = 5 volts,
> 0x00 = 0 volts). It is very linear.
> 
> Each button drives an input port on the
> microcontroller. No keyboard scanning is used.
> 
> To generate tones, an interrupt service routine
> driven
> by an on-chip timer samples a sign wave
> table at 12KHz. The index amount into the table
> determines the frequency. Two indices are
> run. The retrieved values are then summed and
> divided
> by 2. The result is sent to the 8-bit
> output port, which generates the dual-tone waveform.
> Tone duration is accurate to a single
> sampling interval. Frequency acuracy is typically
> within 1 Hz.
> 
> The microcontroller automatically shuts off the
> amplifier and goes into low-power mode
> (microamps) after 5 seconds of inactivity.
> 
> Three modes of operation are supported.
> 
> In MF burst mode (power-up default) the digit
> buttons
> each generate an MF pulse of the
> maximum recommended duration (75 ms.). An additional
> button can be wired to its own pin on the
> micro for 2600, or * and # may be depressed together
> in the MF modes. 2600 plays as long as the
> button is depressed. The * key alone is KP. The #
> key
> alone is ST. The KP burst is timed to 120 ms.
> The ST burst is 75 ms. Pressing keys 1 and 3
> together
> play the STP tone. 4 and 6 play the ST2P tone.
> 7 and 9 play the ST3P tone.
> 
> Depressing buttons 7 and 8 together toggle in and
> out
> of MF continuous mode. A low to high or
> high to low beep confirms the mode change. In
> continuous mode, the MF digits play as long as the
> key is depressed.
> 
> 
> KEYPRESS             DIGIT OR                       
> MF FREQ                CCITT
>                             CODE                    
>  
>         IN Hz                 SYS NO. 5
> 
> 1                              1                    
>  
>         700 +900
> 2                              2                    
>  
>         700 +1100
> 3                              3                    
>  
>         900 +1100
> 4                              4                    
>  
>         700 +1300
> 5                              5                    
>  
>         900 +1300
> 6                              6                    
>  
>         1100 +1300
> 7                              7                    
>  
>         700 +1500
> 8                              8                    
>  
>         900 +1500
> 9                              9                    
>  
>         1100 +1500
> 0                              0                    
>  
>         1300 +1500
> *                              KP                   
>  
>        1100+ 1700                  KP1
> #                             ST                    
>  
>        1500+ 1700
> 1+3                          STP                    
>  
>      900+ 1700                   Code 12
> 4+6                          ST2P                   
>  
>     1300+ 1700                  KP2
> 7+9                          ST3P                   
>  
>     700+ 1700                    Code 11
> 
> KP = Preparatory for digits
> ST = End of pulsing
> STP, ST2P, ST3P = Control codes
> 
> 
> Depressing buttons 8 and 0 together toggle in and
> out
> of DTMF mode. Beeps confirm the mode change.
> In DTMF mode, the 2600 button is not active. The
> digit
> buttons play their corresponding tones in
> continuous mode (burst mode is not supported in DTMF
> mode). Depressing the first and third buttons
> in each row play the DTMF A, B, C, and D tones.
> 
>                                          DIGIT OR   
>  
>                   DTMF FREQ
> KEYPRESS                                CODE        
>     
>                    IN Hz
> 1                                              1    
>  
>                        697   + 12092
> 2                                              2    
>  
>                        697 + 1336
> 3                                              3    
>  
>                        697 + 1477
> 4                                              4    
>  
>                        770 + 1209
> 5                                              5    
>  
>                        770 + 1336
> 6                                              6    
>  
>                        770 + 1477
> 7                                              7    
>  
>                        852 + 1209
> 8                                              8    
>  
>                        852 + 1336
> 9                                              9    
>  
>                        852 + 1477
> 0                                              0    
>  
>                        941 + 1336
> *                                              *    
>  
>                        941 + 1209 
> #                                             #     
>  
>                       941 + 1477
> 1+3                                          A      
>  
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