Software scaling correction

A project log for Open Source FFT Spectrum Analyzer

An FFT spectrum analyzer for machinery vibration analysis, using open source hardware and software

Ariel Quezada 06/07/2016 at 19:310 Comments

The original program was not properly scaled. The signals were plotted using the ADC values and the number of samples obtained.

The signal size has been scaled to g. The ADXL335 has an output from -3g to +3g, for a voltage range from 0 to 3.3 V, that is converted by the ADC to values from 0 to 1023. The original signal is multiplied by 3.0/512, and then the DC offset is determined, taking the average of all the readings. This approach assumes that the average value of the vibration signal is 0.

A correction to the time scale has also been done, considering the sampling rate and the number of samples taken. Frequency range has been limited to 1500 Hz, the maximum frequency that the ADXL335 con provide on the X and Y axes.

The corrected program is, and the resulting plots are now properly scaled.