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Changing Frequencies on the AD8232 Evaluation Board

Question asked by Adrian.Ocneanu on May 16, 2013
Latest reply on May 20, 2013 by Gustavo.Castro
Branched from an earlier discussion

I am trying to start a new thread but not sure how this whole forum works.

 

So I am going to leave my issue here: I am trying to change the frequencies of the low-pass and high-pass filters on the evaluation board.
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Now, to change the two high-pass filters, replacing C6 and C9 from to 0.22uF to 1uF should put both these filters from 7Hz to 1.54Hz. Do you see any problem doing this? (just a check, making sure I am not forgetting anything, my opinion is that it's perfectly kosher to do so).

 

My biggest issue right now is pushing the 25Hz Sallen-Key's cut-off frequency to 50Hz. The first thing I tried was to use a ~250kOhm resistor to replace the 1MOhm R18 resistor. And then read an ECG signal at VOUT.

(surely you can see how decreasing that resistance by a factor of 4 should result in a increase of fc by a factor of 2).

Instead of an ECG signal I found a quasi-square wave one. What it is that I am forgetting here? I did not change the R14C13 nor the R19C15 filters, fyi.

 

Thank you so much for any insight, looking forward to your answer

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