Heart rate 6 click
PID: MIKROE‐3215
Weight: 24 g
Heart rate 6 click is an optical biosensor Click board™ designed for heart-rate
monitoring (HRM). This Click board™ employs a specialized sensor that
incorporates two LED drivers and photo-sensing elements which are the
most sensitive to green light. The green light is most commonly used to
measure the dilatation of the blood vessels, therefore Heart rate 6 is
equipped with two green LEDs, which are driven by the BH1790GLC, a
monolithic integrated sensor for heart rate monitoring. Heart rate 6 click is a
perfect solution for the development of various wearable health-related
devices, smartphones, tablets, and similar space-constrained applications.
It comes in the package which also includes the mikroSDK™ software and a
library with all the functions. The Click board™ comes as a fully tested and
approved prototype, making it a reliable device ready to use on the
development board.
The photo elements inside the BH1790GLC sensor are located behind the
IRCUT filter, which reduces the influence of the IR spectrum of the light.
There is a green filter also, narrowing down the green light responsiveness
even further, which helps to achieve accurate readings, even by using
common green LEDs.
Two LEDs are driven by the BH1790GLC sensor, which provides a constant,
programmable current. The choice of LEDs is not critical at all since the
integrated light filters on the sensor allow only a narrow band of green light
in the range from 520nm to 560nm with 0.8X reduction in respect to the
center frequency (about 540nm). The complete monolithic solution IC with
the two constant current LED drivers, narrow pass-band for the green light
spectrum, low power consumption, and a high integration ratio that allows a
very low number of external components, make the Heart rate 6 click a
perfect solution for development of various wearable health-related devices,
smartphones, tablets, and similar space-constrained applications.
Heart Rate Monitoring or HRM
While the blood passes through the capillary blood vessels, they expand and
dilate. Their light reflectance index changes accordingly. This is the basis of
the photo-plethysmogram (PPM), a method used for the volumetric
measurement of an organ, or in this case - blood vessels. The heart rate
signal is calculated according to the changes of the reflected green light,
sensed by the PD element. The Heart Rate 6 click can provide the HRM
readings by simply placing the index finger over the optical sensor.
How does it work?
Heart rate 6 click is equipped with the BH1790GLC, a monolithic integrated
sensor for heart rate monitoring, from ROHM Semiconductor company. This IC is
a highly integrated optical sensor, very 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 6 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 pulsating frequency of 64Hz or
128Hz. The current through the LEDs can also be programmed in the range
from 0 to 60 mA. Finally, there are two settings for the pulse duration:
0.3ms and 0.6ms. These two values affect the duty cycle of the LED pulses.
Optimal readings can be achieved by balancing these three parameters: the
current amount through the LED (brightness), the speed of the light pulses
(LED frequency), and the pulse width (0.3ms or 0.6ms)
The reflected light burst is detected by a sensing element in a form of a
photo-diode, sampled by a low noise 16-bit A/D converter. The photo-diode
is located behind two light filters which pass only a narrow band of green
light in the range from 520nm to 560nm, with 0.8X reduction in respect to
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 even broader color range LEDs to be used, reducing
the overall cost of the design. However, Heart rate 6 click uses the
KingBright super bright clear green LEDs, with the spectral response that is
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.
Two output registers contain the 16-bit measurement in a form of two 8-bit
words. The upper and the lower 8-bit registers contain the measurement
data, which can be retrieved over the standard I2C interface. The host MCU
can read these registers in cycles of 1/32 sec, or 1/64 sec, depending on the
BH1790GLC settings. The datasheet of the BH1790GLC contains the correct
algorithms, which describe the measurement process with more details.
However, the Click board™ comes with the library which contains functions
that allow measurements to be performed with minimum efforts.
The I2C pins of the BH1790GLC sensor are routed to the respective
mikroBUS™ I2C pins. The I2C bus lines are already equipped with two pullup resistors, which together with the two external LEDs are the only
components required by the BH1790GLC sensor. Pullup resistors are
connected to the 3.3V power rail so that the Click board™ can be used only
with MCUs that use logic levels up to 3.3V for the communication.
Specifications
Type
Biomedical
Applications
This sensor is an ideal solution for development of various
wearable health-related devices, smart phones, tablets, and
similar space-constrained applications.
On-board
modules
BH1790GLC, a monolithic integrated sensor with I2C interface
for heart rate monitoring, from ROHM Semiconductor company
Key Features
A complete monolithic heart rate measurement solution with
two constant current LED drivers, narrow pass-band for the
green light spectrum, low power consumption, and a high
integration ratio that allows very low number of external
components, and more
Interface
I2C
Input
Voltage
3.3V
Click board
size
M (42.9 x 25.4 mm)
Pinout diagram
This table shows how the pinout on Heart rate 6 Click corresponds to the
pinout on the mikroBUS™ socket (the latter shown in the two middle
columns).
Notes
Pin
Pin
Notes
NC
1
AN
PWM
16
NC
NC
2
RST
INT
15
NC
NC
3
CS
RX
14
NC
NC
4
SCK
TX
13
NC
NC
5
MISO
SCL
12
SCL
I2C Clock
NC
6
MOSI
SDA
11
SDA
I2C Data
Power supply
3V3
7
3.3V
5V
10
NC
Ground
GND
8
GND
GND
9
GND
Ground
Onboard settings and indicators
Label
PWR
Name
Default
PWR
-
Description
Power LED indicator
Software support
We provide a library for the Heart rate 6 on our LibStock page , as well as a demo
application (example), developed using MikroElektronika compilers. The demo can run on
all the main MikroElektronika development boards.
Library Description
Library performs the control of the Heart rate 6 Click board via I2C interface.
Library offers a choice to perform a device configuration and a measurement
wait time period, and then can read LED Data. For more details check
documentation.
Key functions:
void uint8_t heartrate6_writeSingleByte( uint8_t regAddr, uint8_t dataIn ) Function writes one byte to the register.
void uint8_t heartrate6_readBytes( uint8_t startAddr, uint8_t *dataOut,
uint8_t nBytes ) - Function reads the desired number of bytes from the registers.
void void heartrate6_getData( uint16_t *ledOffData, uint16_t *ledOnData ) Function reads the LED Data as 16bit unsigned value.
Examples description
The application is composed of the three sections :
System Initialization - Initializes peripherals and pins.
Application Initialization - Initializes I2C interface and performs the device configuration and
reset. After that starts measurement.
Application Task - (code snippet) - Waits until measurement cycle is finished and data is ready
for reading. Then reads the LED Data values and performs the data plotting on serial plot, or
logging on uart. Note : Uart baud rate should be as high as possible, then data plotting will be
more better. I2C clock also should be 100kHz or greater, up to 400kHz, to get better results.
The new measurement cycle is started when command for measurement starting is sent, or
when register 0x57 is read out. Also the pressure on sensor must be same for the all
measurement time, if we want to get the valid results. This is very important to device can work
properly.
void applicationTask()
{
heartrate6_waitMeasure();
heartrate6_getData( &ledDataOFF, &ledDataON );
plotRes( ledDataON );
}
Additional Functions :
void plotRes( uint16_t plotData ) - Performs the data plotting on serial plot.
void logRes() - Performs the data logging on uart.
The full application code, and ready to use projects can be found on
our LibStock page.
Other mikroE Libraries used in the example:
Conversions
I2C
UART
Additional notes and information
Depending on the development board you are using, you may need USB UART
click, USB UART 2 click or RS232 click to connect to your PC, for development
systems with no UART to USB interface available on the board. The terminal
available in all MikroElektronika compilers, or any other terminal application
of your choice, can be used to read the message.
mikroSDK
This click board is supported with mikroSDK - MikroElektronika Software
Development Kit. To ensure proper operation of mikroSDK compliant click
board demo applications, mikroSDK should be downloaded from
the LibStock and installed for the compiler you are using.
For more information about mikroSDK, visit the official page.
https://www.mikroe.com/heart‐rate‐6‐click 11‐20‐18
