Stay connected to your heart's rhythm with BMD101 and PIC18LF46K80

ECG 4 Click is based on the BMD101, a highly integrated specialized bio-signal sensing System-on-Chip (SoC) from NeuroSky, which produces heart-monitoring-related ICs and applications. This IC is the third generation of bio-sensors from this company. It features the complete HR and ECG system on a chip: the analog front-end (AFE) section contains a very precise and low-noise instrumentation amplifier (LNA), which allows very low bio-signals generated by the heart to be amplified enough for the 16-bit ADC to be able to sample them. These voltage impulses are naturally weak and in the range of just a few millivolts, even microvolts. Therefore, any external interferences might obscure them. 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. Therefore, the input signal from the electrodes is processed by several filtering sections, both in the analog (HP filter at the input) and digital domain (LP filter at 100 Hz and BP filter for removing the 50/60 Hz hum from the mains). However, the correct placement of the

measurement electrodes is crucial for accurate readings. More about the electrodes and their placement can be found in the blog article, as mentioned above. ECG 4 Click allows several types of electrodes to be used. It supports both stainless-steel and silver-chloride electrode types. The electrodes are used to perform differential measurements of the voltage generated by the heart. 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. The 3.5mm electrodes connector is further protected by two TVS diodes, which prevent electrostatic discharge (ESD) through the SoC and the Click board™. The absence of the electrodes is detectable by the BMD101, which turns the sensor OFF if there is approximately 19 to 25 MΩ between the electrodes. The BMD101 SoC uses the UART interface for communication. The UART interface works at a 57600 baud rate and has 64 bytes of TX FIFO. It uses the 8-1-1 configuration (1 start bit, 8 data bits, 1 stop bit), allowing communication beyond the

host microcontroller. The UART interface could be used with any USB to UART clicks, allowing the PC or smartphone to process and display the HR and ECG data. More information about the UART interface can be found in the datasheet of the BMD101 SoC. However, provided mikroSDK library offers ready-made functions which speed up the software development process. There is a CS pin on the BMD101 SoC, which is routed to the CS pin of the mikroBUS™. This pin should be set to a HIGH logic level to activate the internal power supply. The RESET pin is routed to the mikroBUS™ RST pin. Setting it to a LOW logic level will trigger a RESET of the BMD101. This Click board™ can only be operated with a 3.3V logic voltage level. The board must perform appropriate logic voltage level conversion before using MCUs with different logic levels. However, the Click board™ comes equipped with a library containing functions and an example code that can be used as a reference for further development.

Curiosity HPC, standing for Curiosity High Pin Count (HPC) development board, supports 28- and 40-pin 8-bit PIC MCUs specially designed by Microchip for the needs of rapid development of embedded applications. This board has two unique PDIP sockets, surrounded by dual-row expansion headers, allowing connectivity to all pins on the populated PIC MCUs. It also contains a powerful onboard PICkit™ (PKOB), eliminating the need for an external programming/debugging tool, two mikroBUS™ sockets for Click board™ connectivity, a USB connector, a set of indicator LEDs, push button switches and a variable potentiometer. All

these features allow you to combine the strength of Microchip and Mikroe and create custom electronic solutions more efficiently than ever. Each part of the Curiosity HPC development board contains the components necessary for the most efficient operation of the same board. An integrated onboard PICkit™ (PKOB) allows low-voltage programming and in-circuit debugging for all supported devices. When used with the MPLAB® X Integrated Development Environment (IDE, version 3.0 or higher) or MPLAB® Xpress IDE, in-circuit debugging allows users to run, modify, and troubleshoot their custom software and hardware

quickly without the need for additional debugging tools. Besides, it includes a clean and regulated power supply block for the development board via the USB Micro-B connector, alongside all communication methods that mikroBUS™ itself supports. Curiosity HPC development board allows you to create a new application in just a few steps. Natively supported by Microchip software tools, it covers many aspects of prototyping thanks to many number of different Click boards™ (over a thousand boards), the number of which is growing daily.