Oximeter 2 Click is a compact add-on board suitable for measuring blood oxygen saturation. This board features the ADPD144RI, a PPG optical sensor for photoplethysmography detection of blood oxygenation from Analog Devices. It combines LED emitters and sensitive 4-channel photodiodes with a custom ASIC that provides optical isolation between the integrated LED emitters and the detection photodiodes to improve the signal-to-noise ratio (SNR). PPG detection of blood oxygenation is achieved by synchronous detection in red and infrared wavelengths. Synchronous measurement allows rejection of both DC and AC ambient light interference with low power consumption. This Click board™ makes it an excellent choice for applications such as optical pulse oximetry and health monitoring.
Oximeter 2 Click is supported by a mikroSDK compliant library, which includes functions that simplify software development.
Oximeter 2 Click 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 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.
Oximeter 2 Click 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, labeled 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.
This 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.
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