instramp:dcfilter
C1 (DC filter)
Now, we add C1 which decouples the 1st and 2nd stage amplifier. It filters out any DC from from by the instrumentation amplifier. Otherwise the gain of 100 of the OP-amp would amplify the DC further and would drive it into saturation. The cutoff frequency is at f=1/(2 pi RC)=0.2Hz but note that it's a first order highpass so that the transition is very wide.
Note that the value of 1uF is OK for EMG (muscle activity) but for ECG (heart) and EEG (brain wave) a capacitor of 4.7uF is recommended (because it's just 1st order).
next step: Ground connections
instramp/dcfilter.txt · Last modified: 2014/05/03 00:33 by berndporr
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Disclaimer: use the information shown on this page and the other related pages at your own risk. See the disclaimer in the CC Attribution-Noncommercial-Share Alike 3.0 Unported license. Safety first: always use an electrically isolated A/D converter for all signal- and power-connections when conducting experiments with subjects. If you measure biosignals from other people you might need to apply for ethical approval. Make sure that the subject is electrically isolated from the mains at all times!
Author: Bernd Porr
Disclaimer: use the information shown on this page and the other related pages at your own risk. See the disclaimer in the CC Attribution-Noncommercial-Share Alike 3.0 Unported license. Safety first: always use an electrically isolated A/D converter for all signal- and power-connections when conducting experiments with subjects. If you measure biosignals from other people you might need to apply for ethical approval. Make sure that the subject is electrically isolated from the mains at all times!
Author: Bernd Porr
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