LP NF switch
I was wondering what is the LP/NF switch on the board that needs a jumper ? Any idea anyone ?
There is an optional Sallen-Key lowpass filter on the cheapstat PCB. The NF setting selects "no filter" and LP setting selects the "low pass" filter. The components R10, R11, C20, and C21 can be used to set the filter parameters. By default these components are left empty - so you can put in whatever you like for this. Also, note that the lowpass filtered values come into the microcontroller on a different ADC then the unfiltered values - ADC_LP on (ADC0) vs ADC_NF on (ADC2). So in addition to adding the hardware components for filter you will need to change this setting in the firmware to read the lowpass filtered values rather than the unfiltered values.
Thanks Will. I'll keep that in mind.
Would you have any feedback on the improvement with such a filter ?
I think you could achieve pretty much the same result (or better) by filtering the data in software after it is collected - when you are analyzing the data.