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  • PIC16LF1718/RN4020 BLE Digital Pedometer

  • Created: Nov 24, 2016

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This reference design features a circuit of a wearable pedometer that can be used for everyday exercise. A pedometer is a tracker that counts each step a person takes by detecting the motion of the person's body. In this design, an accelerometer is used to do the task of sensing the motion. The accelerometer sends the equivalent data of the body motion to the PIC16LF1718 microcontroller that acts as the main controller of this pedometer. The PIC16LF1718 is an 8-bit microcontroller that operates up to 32MHz. It has 28KB flash memory, 2KB RAM, and 24 I/O pins. The PIC16LF1718 microcontroller utilizes eXtreme Low Power (XLP) technology. It features capacitive touch channels, core independent peripherals, 10-bit analog-to-digital converter (ADC), 8-bit digital-to-analog converter (DAC), operational amplifiers, high-speed comparators, etc.

The circuit of this pedometer is mainly composed of the PIC16LF1718 microcontroller, RN4020 BLE module, BMA250E accelerometer, LSHD-7503 7-segment displays, MCP1640T switching regulator, and a MCP1700T LDO regulator. The operation of the circuit is just straightforward. The BMA250E accelerometer counts the steps based on the motion of the person's body. The equivalent data of the number of steps is sent by the BMA250E accelerometer to the PIC16LF1718 microcontroller through I2C communication protocol. The PIC16LF1718 microcontroller then displays the number of steps on the LSHD-7503 7-segment displays. Since there are three 7-segment displays, the PIC16LF1718 microcontroller utilizes a multiplexing technique or an optical illusion in order to control three 7-segment displays with just 11 digital output pins. The user's exercise progress can be tracked also with a smartphone or tablet application. The RN4020 BLE module, which communicates to the microcontroller through serial communication port, allows the pedometer to communicate with a smartphone or tablet.

The whole circuit is powered from a single 3V Lithium coin cell battery. The PIC16LF1718 microcontroller, RN4020 BLE module, and BMA250E accelerometer operate in 3.3V power supply. The MCP1640T boosts the 3V supply from the battery to 3.3V to supply all devices included in the circuit. The MCP1700T LDO regulator only functions when the power source is taken at J1 through a PICkit3 in-circuit debugger or programmer. When PICkit3 is used to communicate with the pedometer, the header J2 selects which device transmits to the PICkit3.