DTMF detetctor

       1209    1336    1477  1633
        |       |       |      |
 697 -- 1 ----- 2 ----- 3 ---- A ----
        |       |       |      |
 770 -- 4 ----- 5 ----- 6 ---- B ----
        |       |       |      |
 852 -- 7 ----- 8 ----- 9 ---- C ----
        |       |       |      |
 941 -- * ----- 0 ----- # ---- D ----
        |       |       |      |

Overview

1) sample:
	measure input using AtoD

2) filter:
	Use A=A*M + input
	or walsh

3) quantify: - every n ms
	scan levels.

   leak values

4) Logic: -  are any tone detectors above a threshold?
	Which Pair are the largest
	Has pair changes since last poll?
	Output Char?

5) serial out
	Send the digit to the serial port

Overview Tone generator

The tone generator uses the catch up call generator.

arrays of quadrature square waves using A= A + M

Every gen_ts seconds add M to A and if gen > max/2 subtract max.

  fr[16],fi[16]

Overview Tone detector

The tone detector uses the sign of the tone generator to add or substract signal.

	arrays of quadrature square waves using A= A + M

Every 1ms add inout  to A and take modulo



function generator_ts( input ){
  // this is called once per measurement of the A/D

  input = input * 1.0

  for ( cnt=0; cnt < 8; cnt++ ){

    // add to the buckets in the proportions required
    // integrate the phase
    generate_r[cnt] += tonesA[cnt]*1.0
    generate_i[cnt] += tonesA[cnt]*1.0

    // leak phase if overflow
    if 	( generate_r[cnt] > gen_ts/2 ) {
	generate_r[cnt] -= gen_ts*1.0
    }

    if 	( generate_i[cnt] > gen_ts/2 ) {
	generate_i[cnt]  -= gen_ts*1.0
    }

    // DFT - if the phase of the square wave >
    if 	( generate_r[cnt] > 0.0 ) {
	measure_r[cnt] += input * 1.0
    } else {
 	measure_r[cnt] += input * -1.0
    }


    if 	( generate_i[cnt] > 0.0 ) {
	measure_i[cnt] += input * 1.0
    } else {
 	measure_i[cnt] += input * -1.0
    }
  }
}