From the board photos that I have seen posted, there are these board header pins for electrode connection:
4 pins for the 4 data channels, one per electrode
1 pin for Reference electrode; typically one ear lobe. Voltage is measured between Reference and each of the 4 channel pins in a differential manner.
1 pin for Ground (DRL, Driven Right Leg, called Bias on the 8 & 16 channel boards.); typically the other ear lobe.
The text on that page also states that "we will also break out up to 20 of the [Simblee] GPIO pins for you to hack with". I dont see that on the front board image; perhaps the breakouts are on the rear board surface.
Joel @biomurph might be able to elaborate on the GPIO pin access. On some uC chips, some GPIOs can operate as extra analog or digital input pins, besides the ones shown on the front of the board. Checking the Simblee specs, analog GPIO inputs operate as 10 bit A/D converters, with 0 and 3.3v being min and max. So these would need amplification to serve as EEG or ECG inputs. EEG signals are in the microvolt range, ECG, millivolt.
Say you had the setup as you said, 4 electrodes to the 4 channels, a reference electrode to REF and another electrode to DRL, what is the use of the AVDD, AVSS and V-REF? Would they be left unconnected?
Oliver, yes, the last three pins you mention are not connected to any electrodes. You could consider them more as internal voltage levels used by the analog to digital converter. The board has separate digital and analog voltage references / regulation, for noise reduction purposes.
Interesting. So as @biomurph has said, this is run by the mcp3912. I was looking at the pinout of that compared to the ads1299. Though I don't get where the DRL and Ground electrode would connect as unlike the ADS, the Mcp doesn't have a bias input?
The DRL/Bias is integrated into the ADS1299 because it is such a comprehensive "does everything" type of solution.
In the case of the Ganglion, the DRL function is not part of the MCP3912, but done externally. Likely linked to a function of the pre-amp, Instrumentation Amplifier chip that sits between the pairs of electrodes (+ and -) and the A/D converter chip.
Comments
- 4 pins for the 4 data channels, one per electrode
- 1 pin for Reference electrode; typically one ear lobe. Voltage is measured between Reference and each of the 4 channel pins in a differential manner.
- 1 pin for Ground (DRL, Driven Right Leg, called Bias on the 8 & 16 channel boards.); typically the other ear lobe.
The text on that page also states that "we will also break out up to 20 of the [Simblee] GPIO pins for you to hack with". I dont see that on the front board image; perhaps the breakouts are on the rear board surface.https://www.google.com/search?q=simblee+gpio
In the case of the Ganglion, the DRL function is not part of the MCP3912, but done externally. Likely linked to a function of the pre-amp, Instrumentation Amplifier chip that sits between the pairs of electrodes (+ and -) and the A/D converter chip.