Hello,
After performing many data captures from a custom designed PCB that entails the ADS1299 and a ATMEL 8bit micro-controller there appears to be some oddities in the signal.
PROBLEM: There is a constant ~13Hz signal that appears on all the channels when connected to the body.
I am using the ADS1299 with a unipolar supply (+5V) and with signal ended inputs (INxP) with a connection to a reference electrode through SRB1.
I have measured the analog supply pins and the VREF pins to see if I could locate the ~13Hz signal. It is not present at those pins and neither at the INxP inputs.
However, I have found that this 13Hz originates from the wireless transmission (2.4GHz Zigbee) emitting from the 8bit zigbee micro-controller, and this can be directly seen on the RFN/RFP 100ohm differential lines, the 13Hz corresponds to the request/transmission rate of the packets.
Measuring the internal noise of the system by shorting internally all channels using CHxSET [0:3] = 001 and sampling the data did not show any signals of ~13Hz.
I then shorted externally the active channels including the bias and references through 6.8k ohm resistors and sampled the data. The ~13Hz was present on only 1 of the channels.
However, when placed on the body, this signal is present on all the channels.
If the signal is present on all channels, should the BIAS be removing this? Below is a picture of the BIAS setup I am using. The BIAS_EIN is connected to the electrode front end shown below, and then to the body through an electrode.
This is the input filter and protection resistor, each channel has this on its input,
I have set the following registers,
PD_BIAS =1
BIASREF_INT = 1
PD_REFBUF = 1
BIAS_MEAS = 0
MISC1 [SRB1] = 1
BIAS_SENSP = [1 for all active channels, 0 for deactivated channels]
BIAS_SENSN = [0 for all channels] ** Is this correct if I am using single ended inputs only through INxP?
Does anyone have any thoughts or issues they see in my configuration?