Your heart's storyteller based on the MAX30003 and STM32F031K6

ECG 3 Click is equipped with the MAX30003, an ultra-low power, single channel, integrated biopotential AFE, with the ECG and R-to-R detection functionality from Analog Devices. ECG 3 click is used to record a single-channel electrocardiogram. Electrodes can be attached to ECG 3 click via the onboard 3.5mm jack. ECG 3 click uses a three-electrode system, where two electrodes are connected to the positive and negative differential input of the MAX30003 (ECGP and ECGN pins), while the third electrode is connected to the GND. The Click board™ can be used with the cable and electrodes such as these: ECG/EMG cable and ECG/EMG electrodes. In this case, the white electrode is the GND electrode. These voltage impulses are naturally weak and in the range of just a few millivolts. Therefore, any interferences might obscure them, making them undetectable. These interferences might be induced in the human body itself or appear as the result of the activity of other muscles, such as skeletal muscles. The MAX30003 is armed with several methods to reduce these interferences. However, the placement of the measurement electrodes is also crucial for accurate readings. The MAX30003 IC has two differential inputs comprising a single ECG channel. Therefore, the heart can be monitored from a single plane only - the coronal plane. However, this is quite enough for fitness, heart rate monitoring, and similar applications. All the mentioned features are mostly related to conditioning the input signal and protecting the IC from voltage surges, so several types of electrodes can be used. The inputs are equipped with a single-pole, high-pass (HP) EMI filter, with the cutoff frequency set to 2MHz,

as the first defense against the interferences. A set of integrated clamping diodes prevent the ESD surges from reaching the IC and damaging it. The inputs are connected with the electrodes over the protective serial switches, which are turned off by default. When developing your own application, care should be taken to turn these switches ON. However, the mikroSDK library functions included with the Click board™ take care of the proper configuring and initialization. The differential inputs are further amplified by an integrated low-noise, high-impedance instrumentation amplifier (IA) with a fixed gain. The IA section features yet another HP filter that helps to reject movement artifacts generated by skeletal muscles. Depending on the application requirements, a higher cutoff frequency will result in a less accurate ECG signal, but the effects of the motion artifacts will be reduced even more. This frequency is determined by a capacitor between the CAPP and CAPN pins of the MAX30003 IC, which is about 0.04Hz, with the 1uF capacitor used on the ECG 3 click. The recommended range for the HP cutoff frequency is from 0.04Hz up to 4.4Hz. Following the IA section, the MAX30003 incorporates the two-pole low-pass anti-aliasing (LP) filter with a cutoff frequency of 600Hz, which ensures good sampling quality. The programmable gain amplifier is the next section in the signal chain, allowing optimal signal amplitudes to reach the next stage - the sigma-delta 18-bit A/D converter, which ultimately generates the heart rate readings over the SPI interface. Other features of the MAX30003 IC include the self-testing programmable voltage sources and no lead detection. One of the key

features of the AFE is the R - R interval detection. R-wave is a part of the heart rate signal with the highest peak. The distance between the two peaks is closely related to the heart rate and can give a good insight into the shape of the R-wave when no plot is available. Closely matched R - R and BPM values indicate that R waves are quite sharp, without irregularities. Also, the BMP (beats per minute) is an average value, while the R - R interval represents the timing between two peaks. The extensive interrupt engine can trigger the host MCU from various sources, including interrupt events due to lead detection, R-R detection, fast-recovery event, FIFO buffer states, and many more. These interrupt sources can trigger a state change on the interrupt pin (INTB) of the MAX30003 IC. This pin is active-low. The MAX30003 IC requires a clock signal provided by the onboard oscillator. The frequency of the oscillator is 32.768 kHz. However, the Click board™ accepts the external clock signal over the PWM pin of the mikroBUS™, labeled as CLK. Regarding the voltage levels, there is a TXB0106 IC implemented on the ECG 3 Click, allowing it to operate with both 3.3V and 5V MCUs. This IC is a bi-directional voltage-level translator from Texas Instruments. It is a proven solution used on many different Click board™ designs, which transforms voltages of the logic signals (SPI, interrupt, clock) to 1.8V-level signals, which is acceptable for the MAX30003 IC. This allows many different MCUs to be interfaced with the ECG 3 click The logic voltage selection can be done with the onboard SMD jumper labeled as PWR SEL, while the clock source can be selected by another SMD jumper labeled as CLK SEL.

Nucleo 32 with STM32F031K6 MCU board provides an affordable and flexible platform for experimenting with STM32 microcontrollers in 32-pin packages. Featuring Arduino™ Nano connectivity, it allows easy expansion with specialized shields, while being mbed-enabled for seamless integration with online resources. The

board includes an on-board ST-LINK/V2-1 debugger/programmer, supporting USB reenumeration with three interfaces: Virtual Com port, mass storage, and debug port. It offers a flexible power supply through either USB VBUS or an external source. Additionally, it includes three LEDs (LD1 for USB communication, LD2 for power,

and LD3 as a user LED) and a reset push button. The STM32 Nucleo-32 board is supported by various Integrated Development Environments (IDEs) such as IAR™, Keil®, and GCC-based IDEs like AC6 SW4STM32, making it a versatile tool for developers.