Hello Suzuki-san, Thank you for your patience while I was out of the office. It is possible for the output of the ADC channel to show an ECG waveform when only one electrode is disconnected. Do you notice the DC level of the channel output shifting when one electrode is disconnected? Depending on the common-mode of each input pin, it's possible to see a small AC signal on top of a large DC common-mode voltage when only one electrode becomes disconnected. To me, this does not indicate an issue with the device. Instead, the firmware should monitor the lead-off status for each input and disregard the channel data when one or both electrodes are disconnected. Figures 25 and 29 of the device data sheet detail the internal MUX and PGA circuitry. Regards, Ryan
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