Power line communication, how to check if frequency is present
FFT is overkill.  Use the Goertzel algorithm to detect a single frequency.


  This effectively implements a second-order IIR filter with poles at e + 2πiω and e − 2πiω, and requires only one multiplication (assuming 2cos(2πω) is pre-computed), one addition and one subtraction per input sample. For real inputs, these operations are real.


"My communication is very simple, if the frequency of the portant is present this is a 1, if not, is a 0."

This is called on-off keying.  I'm not sure if Goetzel is the optimal method for demodulating this in digital, but at least one person recommends it.