We looked around and found in addition to the common MAX30102, this MAX86150 is a nice Integrated Photoplethysmogram and Electrocardiogram Bio-Sensor Module For Mobile Health. Phew, that’s a lot of words, but what it means is that it’s an optical sensor for pulse oximetry with the addition of an EKG analog front end. This is pretty rare – usually there’s one sensor to manage the optical blood-gas sensing and one to do the electrical heart activity sensing. Why both? For telemedicine or self-monitoring, it might be beneficial to see the electrical activity waveforms as well as the SpO2 measurements since they can signify different health issues.
The MAX86150 is an interesting chip in that it has a clear body for IR/Red LED emitting and sensing. Unlike most pulse oximeters we’ve seen, this does not shine light through the finger, it bounces the light off of the finger tip instead. This makes it a simpler wearable, although the cost is a little higher because of the high integration. One cute thing we noticed in the datasheet is that the sensor automatically detects when there’s something in front of the optical sensor, so that it will not keep blasting the high power LEDs, a nice power-saving trick!
The interface for this chip is I2C, so it’s easy to use with just about any chipset. You set the sensor off to collect data and then read the waveform back out. The PPG data is processed by a 19-bit ADC, the EKG is 18-bit and a FIFO collects data in chunks so you can read it at your convenience. Note that the sensor is 1.8V power and logic – it’s designed for low power wearables – so you will need level shifting circuitry for use with 5V or 3.3V microcontrollers & microcomputers.
Best of all, there’s a super-sweet MAX86150 eval board that even has the two ‘dry’ EKG electrodes you put your fingers over. The board is a FeatherWing, and even comes with a MAXIM Feather board, so you can make a portable BLE sensor.
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