Accurate, Finger-Based Heart-Rate Monitoring

Accurate, Finger-Based Heart-Rate Monitoring

Designing a device that measures heart rate and blood-oxygen saturation level (SpO2) from the finger can be challenging. Through a principle called photoplethysmography (PPG), an optical biosensor measures heart rate by shining an LED light into the capillary in the wearer’s tissue at a depth that is sufficient to measure light that has traversed or scattered from the tissue. This movement of light reflects blood volume changes between systolic (when the heart expels blood) and diastolic (when the heart draws blood) heart beats.

Tissue, however, varies quite a lot depending on the person. There are also factors such as optical and physiological noise in the optical path for the monitoring device to address. Highly accurate optical biosensors and precise algorithms are key contributors to a successful wearable health application design.

Maxim has created a new reference design that provides all of the resources needed to quickly prototype a design that measures finger-based heart rate and SpO2. The MAXREFDES220# reference design features embedded algorithms that turn the human-body signals acquired by the platform's sensors into meaningful heart rate and SpO2 data. The algorithms are ready for mass-production consumer products, saving time that you’d otherwise spend writing your own algorithms or validating software from third parties. Instead, you can focus on creating unique applications such as medical-grade consumer devices based on this platform. See Figure 1 for an image of the reference design.

Figure 1. MAXREFDES220#.

The MAXREFDES220# includes:

  • MAX30101 heart-rate monitor and pulse oximeter, which provides > 80dB signal-to-noise ratio, < 1mW operation, and programmable sample rate and LED current in a 5.6mm x 3.3mm x 1.55mm 14-pin optical module
  • MAX32664 Version A ultra-low-power biometric sensor hub, which provides complete algorithmic support for finger heart-rate and blood-oxygen saturation calculations
  • MAX32630FTHR to emulate a host system to ease the development process
  • 3-axis accelerometer, which compensates for motion artifacts for greater accuracy

After the algorithms process the data, the output can be accessed via a PC GUI. One of the unique components of this reference design is the ready-to-use firmware. The firmware and algorithms are encrypted and can be securely loaded to the MAX32664 Version A, which collects and processes the output of the PPG and accelerometer transparently through a dedicated I2C interface. It provides raw as well as processed data. Its 1.6mm x 1.6mm 16-bump WLP allows you to integrate the device into very small designs. See Figure 2 for a block diagram.

Figure 2. MAXREFDES220 block diagram.

Prototyping your design with the MAXREFDES220# can shave off up to six months from the development cycle. So if you want to get a jump on the competition, check out the MAXREFDES220# for your portable healthcare application.