Oxygen and Pulse monitor using NodeMCU

NodeMCU is a commonly used low cost Wi-Fi board. Below is the image of the original board and pinout of the board.

The above NodeMCU board is based on ESP8266 module. The above version of the board is called ESP-12E. This board can be interfaced to a MAX30102 chip for blood oxygen and pulse monitoring. MAX30102 is a Pulse Oximeter and Heart-Rate Sensor for Wearable Health applications.

The pinout and internal block diagram of MAX30102 is as below:

Chip requires 1.8V (VDD) for it's operation and LED requires 3.3V. MAX30102 interfaces to the NodeMCU over I2C interface. MAX30102 has SpO2 sub-system, Temperature sensor. MAX30102 integrates RED and IR LED drivers to modulate LED pulses for SpO2 and heart rate measurements.

When we interface MAX30102 to NodeMCU, there is a incompatibility w.r.t voltage on I2C line. NodeMCU works on 3.3V while  I2C works on 1.8V.

Below is the circuit diagram for the same.

In the above circuit, input power is provided from USB Micro B connector and 5V is translated to 1.8V using on-board regulator. 1.8V power the I2C level translator and SPo2/Heart beat sensor. MAX30102 has two voltage inputs, 1.8V for the supply voltage and 3.3V for the LED supply. For mounting the NodeMCU, two connectors of 1x15 2.54mm pitch are used. 5V is provided to the Vin pin of the NodeMCU. NodeMCU has internal regulator which generates 3.3V. This 3.3V is provided to one end of the I2C level translator.