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ADS1299EEG-FE Issue With Leadoff Detection

Sean Smith39
Prodigy 10 points
Other Parts Discussed in Thread: ADS1299

I'm attempting to use leadoff detection to measure impedance using the ADS1299. My main issue is actually getting it to work. With the 1299 connected to the motherboard, I can do leadoff detection perfectly. Everything works just as advertised. However, when I hook up the 1299 to my device which communicates through SPI, it seems that only Channel 1 works. Channel 1 will do leadoff detection, but other channels only produce a slowly oscillating square wave. The registers I used for the motherboard are here, captured using TI's provided software.  Our registers are exactly the same except for the last bit of Config 3, which appears to be read only and will not flip. I feel like there's some significance there, but I can't quite figure out what.

  • 0
    TI__Mastermind 38745 points
    Hey Sean,

    It looks from you're settings that you are using AC lead-off detection. If you look at the ADS1299 datasheet and skip down to page 43, you will see that bits [1:0] of the LOFF register configure the device to do AC lead-off detection with a 31.2 Hz square wave. From your description, that seems to be exactly what is happening. To use the feature where the LOFF_STAT registers will indicate if the electrodes are connected, you will need to use DC lead-off detection which can be configured by clearing both bits [1:0] in the LOFF register. That feature will not work in AC lead-off since it utilizes a simple comparator to detect a high impedance.

    Regards,
    Brian Pisani