Algorithms
The MAXREFDES106# includes a MAX32674C Algorithm Hub that contains Analog Devices’ proprietary
algorithms for deriving HR from ECG measurement, SpO
2
from PPG measurement, respiration rate from
BioZ measurement, and stroke volume and cardiac output from impedance cardiography (ICG).
Additional analytics such as signal confidence-level are provided to aid the user. These algorithms are
continually updated and improved. So, it is best to use the latest version of the firmware (see the section
Updating the Firmware for more details).
Algorithm Operating Modes
‘Algorithm Hub Mode’
The MAX32666 host MCU firmware contains the sensor drivers to configure and manage the MAX86178
AFE sensor and ADXL367 accelerometer. The host MCU is responsible for reading the raw PPG data
and sending it to the MAX32674C SpO
2
Algo Hub for processing. The AGC is handled by the host MCU
firmware. Timing is more as the host MCU firmware must be able to time multiplex (interleave) tasks
sequentially or run parallel processes that communicate with multiple devices simultaneously.
Impedance Cardiography (ICG)
Note: Starting in 2023, HSP4 modules are updated by adding capacitors to the pads C66 and C68 to
create a 13.5kHz low-pass filter (LPF) on the ECG inputs. This LPF removes the high frequency stimulus
produced by the BioZ drive circuit from reaching the ECG inputs. Older HSP4 patches do not have the
added capacitors and therefore may not be able to perform the ICG measurement. To perform an ICG
measurement with older HSP4s, the HSP4 enclosure can be opened and capacitors (470pF, 0201) can
be soldered to the empty C66 and C68 pads.
To check the version of the patch, look at the sticker on the top of the patch. An updated patch has a ‘V2’
in the bottom left corner, which indicates the added LPF.
Figure 30. Comparison of Original HSP4 to Updated HSP4
The following section discusses how to enable the ICG algorithms output as well as the fundamentals of
the algorithm setup.
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