The MAXREFDES1207 is a reference design for wearable application based on a total Maxim® solution which includes the MAX32660, MAX30112, MAX77651B, and MAX40005. This solution demonstrates how a small size, low cost, low power, high accuracy heart-rate (HR) monitor can be easily implemented. This design can monitor heart rate using two green LEDs.
The MAX30112 is an optimized pulse-oximeter and heartrate AFE for wearable health. It has a high-resolution, optical readout signal-processing channel with built-in ambient light cancellation as well as high-current LED driver DACs to form a complete optical readout signal chain. With external LED(s) and photodiode(s), the MAX30112 offers the lowest power, highest performance heart-rate detection solution for wrist applications. The MAX77651B provides highly-integrated battery charging and power supply solutions for low-power wearable applications where size and efficiency are critical. The device features a SIMO buckboost regulator that provides three independently programmable power rails from a single inductor to minimize total solution size. A highly configurable linear charger supports a wide range of Li+ battery capacities and includes battery temperature monitoring for additional safety (JEITA). The MAX32660 is an ultra-low-power, cost-effective, highly- integrated microcontroller unit (MCU) designed for battery- powered devices and wireless sensors. It combines a flexible and versatile power management unit with the powerful Arm® Cortex®-M4 with floating point unit (FPU). The MAX40005 is a tiny, single comparator which is ideal for a wide variety of portable electronics applications such as cell phones, media players, and notebooks that have extremely tight board space and power constraints. The design also contains an FTDI FT234 USB-to-serial UART interface.
This document describes the hardware shown above and provides a detailed systematic technical guide to designing a small-size, low-cost, low-power, high-accuracy heart-rate monitor. The design has been built and tested, details of which follow later in this document.