R7F0C809+Blood Oxygen Saturation and Heart Rate Measurement

After deciding on the project, we can start the selection of the project plan.

For this non-invasive blood oxygen saturation measurement program(BTW, I recently have written an article analyzing the reliability of smartwatches' Spo2 measurement function, looking forward your opinions), I obtained the following two signal conditioning programs through the Internet and searching for information:

(1) Spo2 probe + discrete components.

(2) Blood oxygen probe + integrated analog front-end chip.

In the selection process of the blood oxygen probe, there are the following two issues that need to be considered:

(1) The size and interface type of the probe.

(2) The type of the probe.

First, based on the board size and portability considerations, the transmissive blood oxygen probe is not ideal. Such probes are bulky, inconvenient to carry, expensive, and the manufacturer has not given clear information.

Secondly, considering price and availability, I chose the DCM03 sensor. The DCM03 integrates 660nm red light, 905nm infrared light, and photoreceiving diodes on a single chip, and the price is relatively cheap, and the information is public.

After selecting the probe, the program selection of the signal conditioning part begins. The discrete-component signal conditioning method is more traditional and has significant price advantages, but its shortcomings are also obvious: its conditioning effect is affected by many factors, including distribution parameters of components, working environment, etc.

In this project, I chose the integrated analog front end AFE4490 produced by TI dedicated to the solution of blood oxygen saturation measurement. This chip includes a low-noise receiver channel with a 22-bit analog-to-digital converter, an LED transmission component, and diagnostic functions for sensor and LED fault detection. The main control chip only needs an SPI interface to communicate with it. It greatly simplifies the traditional discrete component solution, and its VQFN package greatly reduces the PCB area.

For the measurement of heart rate, I chose Sonn Electronics' SON1303+SON3130 supporting signal chain solution. The solution requires only minimal peripheral circuits to work stably without software algorithms for filtering, which greatly reduces the workload of the software part.