Create a pulse_sensor_t instance in main and give it a thresh_setting (this may change per user). Call heart_rate_init(). The PulseSensor outputs an analog pulse signal, so you'll need an ADC to convert the output voltage from the sensor to a digital value the micro can use.
Put this in your super loop in main (psuedocode):
if(adc_data_ready) {
pulse_sensor.signal = adc_data; // pulse_sensor is the pulse_sensor_t instance
pulse_sensor_process_sample(&pulse_sensor, time);
adc_data_ready = false;
}
time is the time interval between process sample function calls, this is used to track the amount of time that has passed and calculating beats per minute, to ensure accuracy I suggest using a capture compare timer task.
A precompiler directive is used to turn debug output on and off. Currently the LOG() macro is defined to use NRF_LOG_INFO which is a Nordic nRF5 SDK specific function, modify this and the includes to fit your micro and environment.