Look at here for program source code. Included files can be downloaded from software library.
1/f fluctuation digitally synthesised has inevitable periodism based on the number of bits used. In this case I used 16 bits and the period of the pattern is not so long. Say about 10 seconds. This may be improved by increasing the calculation bit number.
Anyway this circuit may be good to simulate a bonfire .
I improved calculation resolution from 16 bit to 31 bit, and no periodism was seen. Also I felt the fluctuation was too harsh, and installed a low-pass filter to the output.