In PPG monitor, is Yellow LED used and what is the advantage?

Green/Yellow optical sensor array can provide superior measurement with all skin tones. Better than monitors and watches that employ only green sensors.

For MAX30101, is it necessary to add extra light barrier between chip glass and phone glass?

There are light barriers in the chip module. From chip glass and phone glass, the airgap should be 0.2mm~0.5mm. Normally, we don't add extra light barriers and don't add ink painting on the phone glass inner side.

Why do the green and red LEDs on the mother board keep flashing, when using the MAX30101ACCEVKIT?

If the MAX30101 is disconnected without first exiting the GUI, the firmware on the microcontroller might get corrupted. In this case the two lights on the microcontroller may keep flashing without stopping. In this scenario, the firmware must be reflashed and tested again using the GUI. The suggested software for this operation is Silicon Labs Flash Programming Utility. It is not provided with the EV kit but can be found on the Silicon Labs website.

Is it possible to directly use the daughter board (MAX30101DBEVKIT) with an alternate microcontroller for evaluation, without connecting to the motherboard (USBOSMB)?

Yes, you will be able use the MAX30101DBEVKIT with another microcontroller however, the GUI will only work with the motherboard. The daughter board is simply a platform for the MAX30101 and an accelerometer. Interfacing with it will be very similar to another reference design we offer for the MAX30102 (MAXREFDES117) which is designed to be used with any microcontroller. You will have to pay close attention to the datasheets for both the MAX30101 and the accelerometer.

What are the factors that makes impact on the time delay between AFE conversion start time and PPG Data Ready ?

Following are the factors that affect the time delay - Sample Averaging, the number of LED channels and LED Pulse Width

Why is the time taken for an initial result of HR and SpO2 different ?

In general, HR will be faster than SPO2. HR relies on the principle of peak detection, and uses only one wavelength. SPO2 calculations need to process more raw data, as it relies on the principle of peak to peak amplitude, for two wavelenegths (usually Red and IR). Timeliness depends on the motion and also the perfusion index of the user. Any motion artifact will increase the response time.

If I enable sample averaging in MAX30101/MAX30102 and keep the sampling rate setting to be the same, does the effective sampling rate go down?

The effective sampling rate/throughput would scale proportionally with the number of sample averaging being done. For example, if you set sample average to 2 samples averaged per FIFO sample (set SMP_AVE[2:0] to 001) and set sample rate to 100 samples/sec (i.e SPO2_SR[2:0] to 001), then you will only receive 50 samples per second when reading from the FIFO.

After unzipping the file "MAX30101ACCEVKIT_PCBA.ZIP" I could not find the Gerber files. Can you please advise?

If you download the zip file MAX30101ACCEVKIT_PCBA.ZIP the manufacturing files are there. They are not gerbers, but ODB++. This format is a tgz which is an improved gerber. We have been using the ODB++ for years as the vehicle to transmit manufacturing data to the vendor.

How do I read the FIFO of MAX30101?

Max30101 comes with a FIFO that can hold 32 samples of data. There is one set of red, ir, and green data in each sample. Every data sample occupies 3 bytes. Therefore, if we only care to read the RED and IR LED, then after reading all the samples available, 6 bytes need to be extracted from every sample. The first three bytes are for RED ADC data, and the last three bytes are for IR ADC data. Up to 32 sets of sample data can be saved. Old FIFO data needs to be read before FIFO is full. Once it is full, samples are not pushed onto the FIFO, and they are lost.

How do I set up interrupt for MAX30101/MAX30102 for reading data?

There are two kinds of interrupt sources relevant for reading data from the MAX30101 or MAX30102. The first is A_FULL, which triggers when the 32 samples of FIFO data is about to get full. The number of free samples away from full FIFO can be programmed by setting FIFO_A_FULL[3:0] in the FIFO Configuration register. For example, the interrupt can be triggered when the FIFO is one sample away from being full, or when it is two samples away from being full. The interrupt is cleared by reading the Interrupt Status 1 register (0x00). If A_FULL_EN is set, the master will be informed to read the data via hardware interrupt once the interrupt triggers. Otherwise, the host will have to poll the Interrupt Status 1 register to determine whether the interrupt has occurred. The second is PPG_RDY, which triggers for every new sample of data. The interrupt is cleared by reading the Interrupt Status 1 register (0x00), or by reading the FIFO_DATA register. If PPG_RDY_EN is set, the host processor will be informed to read the data via hardware interrupt once the interrupt triggers. Otherwise, the host will have to poll the Interrupt Status 1 register to determine whether the interrupt has occurred.

How do I configure MAX30101 in Multi-LED Mode?

1. Mode Configuration (0x09): please configure the device in Multi-LED mode by setting bit0-2 of Register 0x09 to 0b111. 2. Multi-LED Mode Control Registers (0x11–0x12): Register 0x11 and 0x12 should be configured as necessary for the end application. For example, to turn on IR, red, and green LEDs, three time slots would be needed. In this case, register 0x11 may be set to 0x21, and register 0x12 may be set to 0x03. 3. LED Pulse Amplitude (0x0C–0x10), The next step is to configure register 0x0C - 0x0F for setting the LED current as shown below. If three time slots were used, only 0x0C-0x0E need to be configured. 4. FIFO Data Register FIFO_DATA[7: 0] 0x07： To read collected data, please perform a read of FIFO data register. The number of bytes to read depend on the number of time slots that are enabled. For example, for three time slots (e.g IR, Red, and Green LED), 9 bytes need to be read to get one sample.

Can Maxim provide the MAX30101 LED location and package details?

If a customer would like to alter the LED and/or photodiode locations or angles on the MAX30101 then the MAX86140 or MAX86141 are the recommended devices to use. However, Maxim can provide the package details to customers with the respective Business Manager's approval. If this is something you're interested in please contact a Maxim Support Applications Engineer for further details.

MAX30101 UV tolerant?

Q: Will there be any degradation of the MAX30101 when it is exposed to UV light, specifically the lens? Will the UV damage the MAX30101 device? A: No, there are no adverse effects to the silicon as a result of moderate UV exposure. Prolonged exposure to UV light can incur aging effects in plastics such as the LED plastic packages and LCP packaging material. Customers that include the MAX30101 in a final assembly that uses UV light to cure composite adhesives of the enclosure should be perfectly fine. Under normal, short duration intense UV light applications (e.g., 60 seconds dental curing used for polarization of light cure composites), there will be no problems to the optical components or the silicon.

Can the IR sensor of the MAX30101 be used to measure body temperature?

Answer: No. The photodiode is optimized for the spectrum of the LEDs used. (The IR LED is 880 nm; the red LED is 660 nm.) Measuring body temperature requires a good response to wavelengths more than 10 times longer, which is not feasible using a silicon photodiode. If non-contact temperature measurement is required then a thermopile -based sensor would be better suited.

Why is the MAX30101 green LED not lighting?

The green LED has a higher turn-on voltage than the red and IR LEDs, so we recommend supplying 4.5-5V to VLED if using the green LED. The green LED also tends to work best with higher current than the red or IR.

What Cover Material Can I Use for the MAX30101, MAX30102, or MAX30105?

Any material with high transmission in the visible range can work as a cover material. Specifically, the spectral response has to be 90% or above for the wavelengths of the LEDs. For MAX30101 and MAX30105, the spectral transmittance response has to be 90% or above around 537nm, 880nm and 660nm wavelengths. For MAX30102, the spectral transmittance response has to be 90% or above around 880nm and 660nm wavelengths. Some materials used in the past are Plexiglass 7N and AF32 glass.

How to select the green LED only on the MAX30101

Multi-LED allows the setting of individual LEDs on the MAX30101 To use only the green LED you can set the mode to Multi-LED by setting MODE[2:0] to 111b (Table 4, page 19) and set the Red LED: LED1_PA[7:0] and IR LED: LED2_PA[7:0] currents to 0. With a green only configuration you will only be able to acquire HR values. The sample rate, pulse width and LED current will also have a considerable impact on power in a wearable application.

Why is the PPG signal saturated when using the MAX30101, MAX30102, or MAX30105?

The LED current may be set too high. Please try reducing the LED Pulse Amplitude.

How can PPG signal quality be improved when measured on the wrist?

Please note that the MAX30101 PPG module was developed for finger applications and not for the wrist. But to improve measurements for wrist-based heart rate applications try the following optimizations: 1. If haven't done already, please use green LED. This is the recommended LED for wrist application as it is less susceptible to motion artifacts and you will get a cleaner signal compared to red and infrared (IR) LED. 2. Please try increasing the LED current and keep the wrist very still. In general, the wrist has a low blood perfusion index so it's more challenging to get a good signal, and the signal is more susceptible to any motion compared to the finger, for example. 3. Please try increasing the sample average. That will reduce the signal noise.

Can 3.3V logic be used for the I2C pins of the MAX30101 even though VDD is 1.8V?

The device I/O can withstand up to 5.5V. The device will function properly when 3.3V is used for the I2C. The only caveat is slightly higher power consumption.