Hi all, I have an application where I would like to get the HART protocol off an incoming 4-20mA signal.

A quick overview HART is an FSK signal superimposed on analog line 1200Hz = "1" 2200Hz ="0".
My hardware is existing so, addition of other Modem devices is not possible.


The input is currently connected to an ADC on a LPC925, where I am measuring the 4-20mA on a slow update. My thoughts were

Speed up the sampling on the ADC to around 8.8kHz (4x Oversample highest HART frequency of 2200Hz),

Then

OPEN TO SUGGESTIONS HERE>>>>


My thoughts are.
Create 2 lookup tables with 4points being the 1200Hz and the 2200Hz voltages with respect to time, then continually compare each sample with both lookup tables, if after 4 samples, I have matches on all points, I have successfully found FreqA or FreqB, if there are no matches then there is noise or no FSK information.

Is this feasible, and logical or is there a better way to do it? Remembering I have only the ADC line and the raw FSK data to play with.


Regards

Marshall