Oximeter 2 Click Board™

How Does The Oximeter 2 Click Board™ Work?

The Oximeter 2 Click Board™ is based on the ADPD144RI, a highly integrated, photometric front end optimized for photoplethysmography (PPG) detection of blood oxygenation from Analog Devices. It combines highly efficient, red and infrared LED emitters, with 660nm red and 880nm IR wavelengths, and a sensitive 4-channel photodiode with a custom ASIC that provides optical isolation between the integrated LED emitters and the detection photodiodes to improve the signal-to-noise ratio. It uses synchronous detection of optical pulses to enhance the rejection of ambient light in addition to low power consumption.

The Oximeter 2 Click Board™ is designed for ultralow direct optical reflections, with independent AFE settings per channel and I2C control interface. The integrated LED emitters produce light pulses synchronous with the active sampling period of the AFE, which consisting of a programmable TIA, a band-pass filter, and an integrator. The processed analog signals are digitized by a 14-bit ADC and summed by the 20-bit burst accumulator. Four simultaneous sampling channels are matrixed into two independent time slots (one for each LED wavelength). An adjustable number of pulses per sample, accumulation, and averaging can be applied to multiple samples to increase the dynamic range to 27 bits.

The Oximeter 2 Click Board™ communicates with MCU using the standard I2C 2-Wire interface, with a typical clock frequency of 400kHz. A high-speed I2C interface allows data to be read from output registers directly or through a FIFO buffer. All register writes are single word only and require 16 bits of data. It also comes with a programmable interrupt line, labelled as INT and routed on the INT pin of the mikroBUS™ socket that simplifies timely data access. The ADPD144RI does not require a specific Power-Up sequence but requires a supply voltage of 1.8V in order to work properly. Therefore, a small regulating LDO is used, the ADP160 from Analog Devices, providing a 1.8V out of 3.3V mikroBUS™ rail.

The Oximeter 2 Click Board™ is designed to be operated only with a 3.3V logic voltage level. A proper logic voltage level conversion should be performed before the Click board™ is used with MCUs with different logic levels. However, MikroE equipped its users with a library that contains functions and an example code that can be used, as a reference, for further development.

SPECIFICATIONS

PINOUT DIAGRAM

This table shows how the pinout of the Oximeter 2 Click Board™ corresponds to the pinout on the mikroBUS™ socket (the latter shown in the two middle columns).

ONBOARD SETTINGS AND INDICATORS

OXIMETER 2 CLICK ELECTRICAL SPECIFICATIONS