Heart rate 4 click

Heart rate 4 click carries the MAX30101 high-sensitivity pulse oximeter and heart-rate sensor from Maxim Integrated. The click is designed to run on either 3.3V or 5V power supply. It communicates with the target MCU over I2C interface, with additional functionality provided by INT pin on the mikroBUS™ line.

MAX30101 sensor features

The MAX30101 is an integrated pulse oximetry and heart-rate monitor module. It includes internal LEDs, photodetectors, optical elements, and low-noise electronics with ambient light rejection.

The MAX30101 integrates red, green, and IR (infrared) LED drivers to modulate LED pulses for SpO2 and HR measurements. The LED current can be programmed from 0 to 50mA with proper supply voltage.

The device includes a proximity function to save power and reduce visible light emission when the user’s finger is not on the sensor.

The MAX30101 has an on-chip temperature sensor for calibrating the temperature dependence of the SpO2 subsystem. The temperature sensor has an inherent resolution 0.0625°C.

Pulse oximetry or SpO2

Oxygen-saturated blood absorbs light differently than unsaturated blood. Pulse oximeters measure the oxygen saturation in one’s blood. Or to put it more precisely the percentage of hemoglobin molecules in blood that is saturated with oxygen.

In a healthy adult, this readings go from 94% to 100%.

How the sensor works

Since oxygen-saturated blood absorbs more infrared light than red light, and unsaturated blood absorbs more red light than infrared light, the SpO2 readings are calculated by the comparison of the amount of these two types of light.

It is best to use your finger for measurement.

The same sensor as Hexiwear

Did you know that this click carries the same sensor as Hexiwear? 

When you place your wrist or fingertip over the slit on Hexiwear, the MAX30101 sensor measures the light absorbance of pulsing blood through a photodetector and derives heart-rate info. Current firmware version is able to show rough estimates.

MikroPlot

You can use the MikroPlot visualization tool (Windows) to generate a graph from the data sent from the MCU.

A UART-USB connection is required.

Specifications

Pinout diagram

This table shows how the pinout on Heart rate 4 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	INT1	Active-Low Interrupt (Open-Drain)
	NC	3	CS	TX	14	NC
	NC	4	SCK	RX	13	NC
	NC	5	MISO	SCL	12	SCL1	2C Clock Input
	NC	6	MOSI	SDA	11	SDA1	I2C Clock Data, Bidirectional (Open-Drain)
Power supply	+3.3V	7	3.3V	5V	10	+5V	Power supply
Ground	GND	8	GND	GND	9	GND	Ground

Jumpers and settings

Programming

Code examples for Heart rate 4 click, written for MikroElektronika hardware and compilers are available on Libstock.

Code snippet

This code snippet initializes the system and display, initializes the board and sets I2C registers. New data from the sensor is collected in a endless loop, via polling and sent via UART to MikroPlot when we are in active heart rate mode.

01  void main( void )
02   {
03     system_init();
04     display_init();
05     hr4_init();
06     hr4_set_registers();
07
08     TFT_Set_Font( &HandelGothic_BT21x22_Regular, CL_RED, FO_HORIZONTAL );
09     TFT_Write_Text( "Use MikroPlot Graph Generator", 10, 100 );
10     TFT_Set_Font( &HandelGothic_BT21x22_Regular, CL_BLUE, FO_HORIZONTAL );
11     TFT_Write_Text( "Place Finger On Sensor", 19, 170 );
12
13     while ( true )
14     {
15       // Clearing the interrupt by reading the Interrupt Status 1
16       if ( hr4_is_new_fifo_data_ready() & 0x1 ) read_f = true;
17
18       if ( read_f )                          // If INT was emitted
19       {
20          read_f = 0;
21
22          if ( !start_f )                     // First start
23          {
24             start_f = true;
25             InitTimer1();                    // Initializing Timer 1
26             LOG("STARTrn");                // Sending START command to uPlot
27          }
28
29          red_sample = hr4_read_red();        // Read RED sensor data
30
31          LongToStr(miliseconds_counter , txt_milis);
32          LongToStr(red_sample , txt_val);
33          Ltrim(txt_val);
34          Ltrim(txt_milis);
35
36          // If sample pulse amplitude is under threshold value ( proximity mode )
37          if ( red_sample > 0 && red_sample < 32000 )
38          {
39            stop_f = true;
40            if ( !no_finger_f )
41            {
42              TFT_Rectangle( 19, 170, 310, 200 );
43              TFT_Write_Text( "Place Finger On Sensor", 19, 170 );
44            }
45
46            no_finger_f = true;
47          }
48
49          // If finger is detected ( we are in active heart rate mode )
50          else if( red_sample != 0)
51          {
52              stop_f = false;
53
54              if ( no_finger_f )
55              {
56               TFT_Rectangle( 19, 170, 310, 200 );
57               TFT_Write_Text( "Generating Graph...", 19, 170 );
58              }
59
60              no_finger_f = false;
61
62              // Sending data to MikroPlot in format:[pulse_value, milis] via UART
63              LOG(txt_val);
64              LOG(",");
65              LOG(txt_milis);
66              LOG("rn");
67          }
68       }
69     }
70   }