DTMF.cpp gets compile errors for me. I use the current version of the 'arduino' package from the Fedora 'updates' repository on Fedora 20. Perhaps something has changed in the avr-gcc compiler. I get error message:
unable to find a register to spill in class 'POINTER_REGS'
The line causing the error is:
dtmf_mag = sqrt(Q1Q1 + Q2Q2 - coeffQ1_Q2);
I fixed the problem by splitting up this expression into 3 lines:
float tmp;
tmp = Q1*Q1 + Q2Q2;
tmp = tmp - coeff*Q1Q2;
dtmf_mag = sqrt(tmp);
Griff_