Easy Pulse mikro is our new educational pulse sensor in a mikroBus form factor. Like our previous Easy Pulse sensors (Easy Pulse and Easy Pulse Plugin), it is also based on the principle of transmittance photoplethysmography (PPG) applied to a fingertip. The sensor consists of a pair of IR LED and photodiode to detect the cardiovascular pulse signal from the fingertip. The output of the sensor is passed through a necessary instrumentation amplifier to derive a nice and clean analog PPG waveform. The analog output is routed to the AN pin of the mikroBus connector. In this article, I will describe how to use the Easy Pulse mikro sensor with Microchip’s latest MPLAB Xpress development board for uniform ADC sampling of the analog PPG signal and sending the samples to a PC for post digital processing in order to retrieve the heart-beat rate. Currently, you can buy this sensor from our Tindie Store in United States and Elecrow Store in China.
MPLAB Xpress Board
In this section, I will provide a brief overview of MPLAB Xpress board and its features.
Features
The MPLAB Xpress Evaluation Board features PIC16F18855, an 8-bit PIC processor with Core Independent Peripherals (CIPs) combined with eXtreme Low Power (XLP) technology suitable for a wide range of general purpose and low-power applications. CIPs in PIC MCUs, once initialized, can handle their tasks with zero intervention from the core (or CPU), thereby simplifying the design of embedded systems. During CIP operations, the CPU is free to perform other system tasks, if available, or can be idled and put into sleep mode to save system power. For the details of the available CIPs on PIC16F18855, refer the datasheet. The PIC16F18855 features 14 KB of program memory, 1024 bytes of RAM, and a configurable (up to 32MHz) internal oscillator. The I/O pins are brought to two rows of blank headers (0.1″ pitch) on opposite edges of the board. There are four red LEDs (with current limiting resistors) connected to I/O pins RA0 through RA3 and the EMC1001 I2C temperature sensor pre-installed on the board. A 10K potentiometer is also available (potentiometer output goes to RA4/ANA4 pin) for a quick analog-to-digital conversion demo. The availability of a mikroBus socket on board allows a simple Plug-and-Play solution for connecting mikroElektronika’s accessory boards (called Click Boards) that would greatly enhance the capability of MPLAB Xpress board.
On-board Programmer
The MPLAB Xpress board also carries an onboard programmer using the PIC1825K50 microcontroller that emulates as a USB storage device, thereby offering a driver-free plug and play USB interface. The HEX file can be uploaded to the target PIC16F18855 MCU through a simple drag and drop operation.
Power supply
The MPLAB Xpress board is receives a 5V power supply through the micro USB connector. There is a 3.3V regulator circuit on-board to provide VCC supply to both PIC MCUs. The un-regulated 5V from the USB port and the regulated 3.3V output are also accessible at the blank headers and the mikroBus socket pins. The board also allows an external power supply (VIN) that goes to the input of the 3.3V regulator circuit. Because there is no 5V regulator on board, the VIN supply goes directly to all the pins that are marked as 5V. So you should be careful in case you would like to power the Xpress board with an external power source. Make sure VIN is a regulated +5V.
Thanks to Jason Wellman from Microchip for providing a free sample of MPLAB Xpress board.