Heart Rate 10 Click is a compact add-on board suitable for heart rate monitoring applications. This board features the MAX86916, an integrated optical sensor with applications in bio-sensing, proximity, and color from Analog Devices. The module includes internal LEDs, photodetectors, and low-noise electronics with ambient-light-rejection circuitry and establishes communication to and from the module entirely through a standard I2C compatible interface. It operates on a 1.8V supply voltage with a possibility to be shut down through software with a near-zero standby current, allowing the power rails to remain powered at all times. This Click board™ is suitable for optical pulse oximetry and heart-rate detection applications.
Heart Rate 10 Click is supported by a mikroSDK compliant library, which includes functions that simplify software development.
Heart Rate 10 Click as its foundation uses the MAX86916, a multipurpose optical sensor with applications in Heart Rate (HR) monitoring and as a medical-grade pulse oximeter from Analog Devices. The MAX86916 integrates four LED drivers and BLUE, GREEN, RED, and INFRARED LEDs. The LED current can be programmed from 0mA to 150mA, and pulse width can be programmed from 70μs to 420μs to allow the algorithm to optimize data acquisition accuracy and power consumption based on use cases. Also, the MAX86916 includes a proximity function to save power and reduce visible light emission when the user’s finger is not on the sensor.
The receive path in the MAX86916 is composed of an ambient-light-cancellation (ALC) circuit, a continuous-time sigma-delta ADC, and a proprietary digital filter that rejects slow-changing ambient light including 100Hz/120Hz interference from artificial lights. The ALC is designed to cancel ambient-light-generated photodiode current up to 200μA, allowing the sensor to work in high ambient light conditions. When the ambient light cancellation function reaches its maximum limit, due to overflow from strong ambient light, the output of the ADC is affected, and the Ambient Light Cancellation Overflow interrupt, labeled as INT and routed on the INT pin of the mikroBUS™ socket, is generated to detect this condition.
The MAX86916 does not require a specific Power-Up sequence but requires a supply voltage of 1.8V to work correctly. Therefore, a small regulating LDO is used, the MAX8511 from Analog Devices, providing a 1.8V out of both 5V and 3.3V mikroBUS™ rails.
Heart Rate 10 Click communicates with MCU using the standard I2C 2-Wire interface with a maximum clock frequency of up to 400kHz. It is fully adjustable through software registers, and the digital output data is stored in a 32-deep FIFO within the device. Since the sensor for operation requires a power supply of 1.8V, this Click board™ also features the PCA9306 voltage-level translator from Texas Instruments. The I2C interface bus lines are routed to the dual bidirectional voltage-level translator, allowing this Click board™ to work with both 3.3V and 5V MCUs properly.
This Click board™ can operate with both 3.3V and 5V logic voltage levels selected via the VCC SEL jumper. This way, it is allowed for both 3.3V and 5V capable MCUs to use the I2C communication lines properly. However, the Click board™ comes equipped with a library containing easy-to-use functions and an example code that can be used, as a reference, for further development.
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