Why does quality of the HR and SpO2 reading from the MAX30101 decrease when my finger is cold?

This result is expected. This is not because of the MAX30101/2, but rather because of the PPG signal itself. Colder temperatures reduce blood flow, which results in a reduced PPG signal quality. This affects our algorithm’s ability to detect heart rate and SpO2. I would recommend looking at this research paper if you would like to learn more about this topic: https://www.sciencedirect.com/science/article/pii/S2405896315020571

How to avoid water condensation inside the MAX30101/5?

Unfortunately the 14 pin OLGA package has a vent hole at the bottom and this cannot be avoided, you need to use the device in a noncondensing environment. This is the risk of open packages. If you seal it, a strong pressure differential might cause lid to break/pop off.

For the MAX30101 in HR mode (no green LED) is it acceptable to power the VLED from an unregulated source such as a Li-ion battery (3.0-4.2V)?

As the internal LED drivers of the MAX30101 use current regulation, the VLED connection can be powered from an unregulated voltage source. If you are not using the green LED, then the acceptable voltage range is 3.1V minimum to 5V maximum, which covers most of the voltage range of a Li-ion cell.

Is there any wake up delay after toggling the SHDN bit in the MAX30101?

SHDN just disables the sampling part of the chip but doesn’t actually power down any of the critical parts of the chip, so there is no wake-up delay. There is only a delay if the part is RESET or power cycled.

How can we stop the MAX30101 from collecting data without disrupting the communication or resetting the registers?

The SHDN bit can be toggled to stop the part from collecting data without disrupting the communication or resetting any registers

Are larger currents better for the MAX30101 luminous tube?

Considering power consumption and effective resolution, it is not better to have a larger current. However, for some parts to be measured (such as a wrist), or objects to be measured (such as people with darker skin color and people who are physically overweight), the current of the luminous tube needs to be increase to effectively obtain the strength of the available signal and obtain the measured value.

Can the luminous intensity of the MAX30101 LED be independently adjusted?

The current of the LED can be adjusted; the maximum is 50mA. In addition, the pulse width of the current can also be adjusted. The range of adjustment covers 4 stages. Every LED light signal can be adjusted independently.

Can a single crystal oscillator be shared between multiple ICs ?

While its not usually advisable to share a crystal between ICs, it can be done if the following constraints are considered: The traces from the crystal to the ICs should be as short as possible. Proper care should be taken to ensure the impedance matching between the paths. Both ICs are configured to expect the clock as an input and not drive the crystal. Care should be taken to not overload the crystal with load capacitance.

What should be the spectral response of the cover window material for the MAX30101?

For the MAX30101, the spectral response has to be 90% or above around 537nm, 880nm and 660nm wavelength.

How to minimize error due to the self-heating effect of the LED’s in the MAX30101?

A large thermal mass should be provided on the PCB to sink heat out of the MAX30101 via pins 8-10. As this thermal pad can also conduct heat into the part, these pins should be oriented as far from any external heat source as possible. Ideally, the component should be oriented such that any heat from an external source is centered along its axis to minimize any thermal gradients across the pins/die.

Is it possible to relocate the three electrodes from the chest to the human body backside for BioZ?

The electrodes can be placed on the back. However placing the electrodes on the back will affect the signal amplitude and may result in unwanted movement artifact being added from the back muscles (Infraspinatus fascia, Latissimus dorsi, etc...).

Is it recommended to use two green LEDs for heart rate measurement using the wrist?

Many HR wrist bands use 2-LEDs. However, they are typically matched, positioned symmetrically to the Photodiode centroid, have the same height, and implement optical walls to reduce cross coupling. One external LED can be used with MAX30101 to have two LED solution with one embedded and one external LED. However, matching is not viable as the external LED needs to be exactly matched with the embedded LED. In addition an optical barrier (i.e., light absorbing wall) is recommended between an external LED and the Photodiode.

What is the recommended connection of pins 5, 6, 7 in the MAX30101?

In the MAX30101 datasheet, pins 5,6,7 are NC. But in the MAX30101 Eval kit datasheet, these 3 pins are connected to an LED. What are the function of these 3 pins ? They are there primarily for production test. However, parallel external LEDs can be used with caution. The drive current will split between the internal LED and the external LED. Matching the LEDs will not be viable. In addition, the external LEDs will need to have v-drop compliance for the system. If this device is used for SpO2, there will be performance issues associated with simultaneous emission of two different wavelengths. For SpO2, The ratio of Red/IR is used to estimate SpO2. The Green LED, typically used for heart rate measurements, will probably be a little more tolerant to an external green LED. This emission does not involve a post processing ratio calculation, but rather identification of Pk-Pk timing.

What are the optimal current values for the LEDs in the MAX30101 for wrist-based biosensor measurements?

You can use the following settings as a starting point for wrist-based measurement. The green LED generally needs much more current than the red and IR for good results. To evaluate the quality, you should place the module against your wrist and then plot each color vs time and look for distinctive peaks for each heart beat. If the plot shows a straight line, then the ADC is saturated and the LED current is too high. If you just see noise, try increasing LED current or adjusting the sensor on your wrist. Here are the recommended starting point settings: Pulse width: 411us ADC Full Scale: 8192nA Red: 10mA IR: 10mA Green: 50mA

Is there minimum requirement for the cover glass thickness of MAX30101?

The cover glass thickness is entirely up to the customer's design. The main consideration is to choose a material with >90% light transmission at red/green/IR wavelengths.

What is an OHR solution?

An OHR solution is an Optical Heart Rate solution. The OHR abbreviation is often used in relation to our Optical sensor based parts.

Can MAX30101 be used to measure the respiratory rate?

Yes, the MAX30101 can be used to extract the respiratory rate. While traditional methods of respiratory rate measurement involve using a strain gauge to measure the expansion of the chest to measure respiration, the same data can be extracted from the PPG signal by processing the signal via Empirical Mode Decomposition technique which is particularly suitable for wearables. You may find the following link to be quite helpful: https://ieeexplore.ieee.org/document/7348369

Is there a way to change the I2C address of the MAX30101 or MAX30102?

Unfortunately there is no way to change the default I2C address of the MAX30101/2. If you require more LED's on the same bus consider using the MAX86140/1 AFE which feature an SPI interface and allow for a number of different configurations for arrays of LEDs as detailed in the datasheets.

Can the systolic blood pressure be obtained from the PPG and ECG signals?

While there is no direct way to obtain the exact value of blood pressure from PPG and ECG signals, mathematical models can be used to estimate the blood pressure information. A popular way of doing so is to use ECG-PPG heartbeat pairs to determine pulse transit time (PTT) measurement which is then used in a PTT&HR-SBP model for systolic blood pressure application. You may find the following links to be quite useful: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5294811/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4512231/

Questions on application note 6547

Questions: a) On page 4 there´s a table (figure 2) with systolic and diastolic peaks. Do I get blood pressure automatically from the PPG wave ? b) Is it a finger or wrist based PPG signal ? Answers: a) The blood pressure cant be obtained from the PPG signal alone. Both the PPG and EEG signals are needed to obtain the blood pressure. The figure is used to illustrate the temporal location of systolic and diastolic peaks with relation to the PPG signal. b) The signal waveform corresponds to reflective PPG. The diagram is used for illustration purposes and the location of the signal cant be detected from the PPG signal.