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I am using the Sparkfun Development kit based on AD8232 for acquiring the ECG signal from the body. Sparkfun Kit. Now I am getting a perfect ECG signal when I turn off all the power in the house and then view the signal; however this is far from my practical scenario. So I have been looking into designing a Notch filter to remove the PL frequency (50-60Hz). I have tried the following, without success:

  • Notch filter I have tried more but I am unable to post links; apparently I don't have enough repo. Anyway, I would appreciate it if someone can shed some light in this regard. I have tried Twin T notch with 2 opamps as well. Nothing seems to help.
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    \$\begingroup\$ Have you looked at the right leg drive connection for the kit? The data sheet for the AD8232 mentions this specifically for use in reducing power line interference. \$\endgroup\$ – JRE Jun 15 '16 at 7:49
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    \$\begingroup\$ Also, C2 is 10 times what the datasheet recommends. The higher value will increase the amount of line noise. Try replacing C2 with 1nF as the datasheet recommends. \$\endgroup\$ – JRE Jun 15 '16 at 8:01
  • \$\begingroup\$ Yeah I have. The RLD doesn't really help. Also, we're using a 2-lead configuration, so RLD is shorted to RA. \$\endgroup\$ – Richeek Dey Jul 12 '16 at 9:13
  • \$\begingroup\$ RLD doesn't really help. Also, we're using a 2-lead configuration so RLD is shorted to RA. \$\endgroup\$ – Richeek Dey Jul 12 '16 at 9:13
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In the past I have built power line frequency rejection filters using switched capacitor notch filters. A chip like the Maxim MAX7490 may work for your application where you can apply an external clock signal to set the notch rejection frequency. There are a few other similar parts from other vendors as well.

Keep in mind that as well as needing to filter 50/60 Hz from your signal it will highly likely be that you will also have to filter out 100/120 Hz as well.

These days with the availability of high performance low cost DSP devices such filtering is often done using software filtering techniques.

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If you are using a power supply for the ad8232, you will introduce the noise from the electrical network into the circuit. What you should do is the following: use a battery to power the circuit, this chip is designed to operate with batteries. The RLD circuit must reject the noise from the electrical network. Another factor from own experience is that the length of the electrodes influences to generate a lot of noise, the shorter they are, the lower the noise. Ideally, you should also have electrodes that have shielded cable. Using a notch can cut important frequencies of the ECG.

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