ADS1291: Questions about ADS1291

Hello Yihui ,

Thanks for your post and welcome to our forum!

yihui zhu said:

1.  What is the value of 95% in the red arrow in the figure below? Which 95% of the value?

The settings listed in the LOFF[7:5] bits are the threshold voltages given as a percentage of the supply voltage (AVDD - AVSS) with respect to AVSS. For example, 95% for bipolar 5-V supply (+/- 2.5 V) would set the positive threshold at 0.95 * 5 V + (-2.5 V) = 2.25 V.

yihui zhu said:

2.I can now collect the ECG signal of the ECG simulator. There is a QRS wave, but I can't acquire the ECG signal on the arm. When I collect the ECG signal from the human body,

what are the major parameters to adjust? The schematic is as follows：

There are many possible answers to this. First, I would substitute a real ECG input with a function generator. This will provide a controlled, consistent signal source as you evaluate and adjust your design. Most likely, the high electrode impedance is attenuating the smaller portion of the ECG waveform such that it disappears below the noise floor. 

I don't see anything immediately wrong with your schematic. Try to adjust the gain and data rate settings to maximize the noise performance and dynamic range of the ADC. 

yihui zhu said:

3.  There is a question about DVDD power,When VDD_EN is enabled via the GPIO port, VDD has 3.3V supply, but using a multimeter to test the DVDD of ADS1291,

the voltage is only 2.74V. This should be abnormal? Should be 3.3V normal. What should I pay attention to when powering up?

Can you also measure the current drawn by the ADS1291 DVDD pin? Most likely, the supply source is being loaded by other circuitry or it is not regulating properly by itself. What is the source of the 3.3 V? Are there other devices using the same 3.3 V supply?

Best Regards,