Get to know your heart with BH1792GLC and PIC32MZ2048EFH100

Heart rate 8 Click is based on the BH1792GLC, a monolithically integrated sensor for heart rate monitoring, from ROHM Semiconductor. This IC is a highly integrated optical sensor well-suited for performing PPM measurements. Due to the large integration scale of this sensor, as well as its low power consumption, it is perfectly suited to be used on a wearable IoT device. However, being a Click board™, Heart rate 8 click allows easy evaluation and rapid application and firmware development. Two green LEDs are driven by the integrated LED driving section of the BH1790GLC sensor, with the programmable Synchronized Measurement mode, with a measuring frequency between 32Hz and 1024Hz. While in this mode, two green LEDs will operate at various frequencies between 32Hz and 1024Hz, depending on the MSR bits of the measurement mode register. This allows automatic LED burst rate adjustment for achieving optimal readings. In this mode, a programmed number of measurements will be performed, and the readings will be stored on the 35 samples' deep FIFO buffer. LED current can be programmed from 0 to 63 mA, providing another control layer while using this mode. Upon receiving the MEAS_SYNC command, the measurement is performed by setting the MEAS_SYNC bit to logic 1. There are also two additional modes: Non-Synchronized, and Single Measurement mode, both allowing the IR LED to

detect an IR-emitting object, such as the hand or finger. The current through the LEDs can also be programmed from 0 to 63mA for both the IR and the green LEDs. Non-Synchronized mode offers a fixed 4 Hz LED burst operation, while the Single Measurement mode allows manual control of all the parameters. No data will be stored on the FIFO buffer in this mode. Upon receiving the MEAS_ST command, the measurement is performed by setting the MEAS_ST bit to logic 1. The reflected light burst is detected by a sensing element as a photo-diode, sampled by a low-noise 16-bit A/D converter. The photo-diodes are located behind two light filters which pass only a narrow band of green light in the range from 520nm to 560nm, with a 0.8X reduction in the center frequency. The top filter is an IRCUT filter that prevents the influence of the IR light, while the second filtering layer only passes the green light. This allows an even broader color range of LEDs to be used, reducing the overall cost of the design. However, Heart rate 8 click uses a pair of specialized green LEDs with a spectral response closely matched to the passband properties of the optical filter. This allows most of the LED energy to be used, further improving the power consumption profile. The second A/D converter does not filter light, allowing the light from the IR diode to be sensed. This is useful when a separate detection of the IR spectrum is required, for example, to detect an

approach of the finger. The IR LED driver is physically shared with the second green LED driver, but the IR LED has its dedicated pin. Two sets of four output registers contain the 16-bit measurement data in the form of two 8-bit words for the measurement when the LEDs are ON and when the LEDs are OFF. The upper and the lower 8-bit registers contain the measurement data, which can be retrieved over the standard I2C interface. The datasheet of the BH1792GLC contains the correct algorithms, which describe the measurement process in more detail. However, the Click board™ comes with the library, which contains functions that allow measurements to be performed with minimum effort. A dedicated programmable INT pin can signal an interrupt to the host MCU. The interrupt can be triggered for several events, including the data ready event (measurement completed), an event when the IR threshold is exceeded, and a so-called watermark event when the FIFO buffer is nearly full. It can also be completely disabled. The INT pin is routed to the INT pin of the mikroBUS™. A low number of external components required by the BH1792GLC sensor allows enough room on the Click board™ for the PCA9306 IC, a well-known I2C level translator, allowing the Heart rate 8 click to be interfaced with many different MCUs, both operating with 3.3V and 5V logic levels.

Flip&Click PIC32MZ is a compact development board designed as a complete solution that brings the flexibility of add-on Click boards™ to your favorite microcontroller, making it a perfect starter kit for implementing your ideas. It comes with an onboard 32-bit PIC32MZ microcontroller, the PIC32MZ2048EFH100 from Microchip, four mikroBUS™ sockets for Click board™ connectivity, two USB connectors, LED indicators, buttons, debugger/programmer connectors, and two headers compatible with Arduino-UNO pinout. Thanks to innovative manufacturing technology,

it allows you to build gadgets with unique functionalities and features quickly. Each part of the Flip&Click PIC32MZ development kit contains the components necessary for the most efficient operation of the same board. In addition, there is the possibility of choosing the Flip&Click PIC32MZ programming method, using the chipKIT bootloader (Arduino-style development environment) or our USB HID bootloader using mikroC, mikroBasic, and mikroPascal for PIC32. This kit includes a clean and regulated power supply block through the USB Type-C (USB-C) connector. All communication

methods that mikroBUS™ itself supports are on this board, including the well-established mikroBUS™ socket, user-configurable buttons, and LED indicators. Flip&Click PIC32MZ development kit allows you to create a new application in minutes. Natively supported by Mikroe software tools, it covers many aspects of prototyping thanks to a considerable number of different Click boards™ (over a thousand boards), the number of which is growing every day.