RC and MAX292 low pass filter testing notes

 

Now I have separately tested the RC and MAX292 low pass filters and found them not too different in performance.  I then cascaded RC output to MAX292 input and made a record of the cascaded performance, actually not too much different from either one alone.

The MAX292 low pass filter circuit is summarized below.

1.  Xtal oscillator is 2.048 MHz.

2. HC4040 12 stage ripple binary counter inputs 2.048 MHz clock.  Its' outputs Q11, Q10, Q9, Q8 (1 kHz, 2kHz, 4 kHz, and 8 kHz)  can be selected to be the clock of MAX292 low pass filter, with corresponding corner frequencies of 10, 20, 40, 80Hz.  I found 40Hz best for filtering ECG signals.

The ECG signals cannot be repeated easily, because of the electrode placement positions, and conact resistance.  So I am thinking of making a calibration signal to calibrate the ECG module and low pass filters.

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