Wednesday, June 12, 2024

Heart-Rate Monitor Wrist Band Reference Design

The design features compact components suitable for creating efficient heart rate monitors with advanced functionality and performance.

wrist band

Wearable devices are valued for compactness, often designed to be as small as conventional watches, wristbands, or finger scanners. As technology progresses, the challenge for designers is to integrate an increasing number of functions into these devices, with the size of each component playing a critical role in how many features can be included. Additionally, these devices are optimized for low-power usage, utilizing batteries as their primary power source. Given the limited size and energy capacity of the batteries, this is crucial to extend the device’s operational life. Most wearable devices operate in standby mode over 90% of the time, making low standby power consumption vital. Furthermore, as market demands shift towards higher precision, the accuracy of these devices has become a critical selling point, with only the most precise devices gaining acceptance in the market. The MAXREFDES1207 from Analog Devices (ADI) is a reference design tailored for wearable applications.

It incorporates the MAX32660, MAX30112, MAX77651B, and MAX40005 components. This design facilitates the creation of a compact, cost-effective, low-power, and highly accurate heart rate monitor using two green LEDs.

The MAX30112 is a specialized pulse oximeter and heart rate analog front-end (AFE) designed for wearable health applications. It features a high-resolution optical signal processing channel with ambient light cancellation and high-current LED driver DACs, creating a complete optical signal chain. Using external LEDs and photodiodes, the MAX30112 provides an optimal solution for heart rate detection in wrist-worn devices due to its low power consumption and high performance. 

The MAX77651B enhances the design with an integrated battery charging and power management solution, which is crucial for wearable devices where size and efficiency matter. It includes a SIMO buck-boost regulator, which delivers three separate power rails from a single inductor to reduce the overall size. It also features a versatile linear charger supporting various Li+ battery sizes and monitoring battery temperature for added safety (JEITA standards). 

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The MAX32660 is an ultra-low-power, cost-effective microcontroller (MCU) suitable for battery-operated devices and wireless sensors. It merges a flexible power management unit with a powerful Arm® Cortex®-M4 processor equipped with a floating-point unit (FPU). 

The MAX40005, a compact single comparator, is perfect for portable electronics with severe space and power limitations, such as cell phones, media players, and notebooks. Additionally, the design includes an FTDI FT234 USB-to-serial UART interface.

The main features and benefits of the design include an integrated solution that ensures a seamless performance, compact size for convenience and portability, low power consumption for extended use, and high accuracy in its functionality. These attributes make it suitable for users seeking efficiency and reliability in a single package.

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ADI has tested this reference design. It comes with a bill of materials (BOM), schematics, a printed circuit board (PCB) layout, etc. You can find additional data about the reference design on the company’s website. To read more about this reference design, click here.

Nidhi Agarwal
Nidhi Agarwal
Nidhi Agarwal is a journalist at EFY. She is an Electronics and Communication Engineer with over five years of academic experience. Her expertise lies in working with development boards and IoT cloud. She enjoys writing as it enables her to share her knowledge and insights related to electronics, with like-minded techies.

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