SLAA486B January   2011  – June 2019 MSP430G2452

 

  1.   EKG-Based Heart-Rate Monitor Implementation Using the MSP430G2xx LaunchPad™ Development Kit
    1.     Trademarks
    2. 1 Introduction
    3. 2 Hardware Description
      1. 2.1 Hand Detection Circuit
      2. 2.2 Analog Front End (AFE)
      3. 2.3 Pin Functionality Mapping on the LaunchPad Kit
      4. 2.4 eZ430 RF Target Header
      5. 2.5 Power Supply Setup
    4. 3 Software
    5. 4 References
  2.   A Amplifier Options
    1.     A.1 Instrumentation Amplifier Options
    2.     A.2 Operational Amplifier Options
  3.   B Wired USB Demo With Back-Channel UART
  4.   C Wireless UART Demo With the eZ430 RF Target Board
  5.   D Hardware Schematic Diagrams
  6.   Revision History

2.1 Hand Detection Circuit

A resistor divider scheme is implemented to detect contact of the subject’s finger tips with the conductive pads. The premise of this scheme is that the resistance of the human body between the finger tips is in the range of 100 kΩ to 300 kΩ, and the resistance placed between the conductive pads is significantly greater than this range, as Figure 2 shows.

hand_detection_circuit_diagram_laa486.gifFigure 2. Hand Detection Circuit Diagram

When contact is made, the current flows through the path of least resistance (the human body) causing the voltage at the left conductive pad to change. This voltage is sampled by an analog-to-digital converter (ADC) channel and the digital conversion result is compared against a set of thresholds to determine good, bad, or no contact. Power and ground are supplied from the microcontroller pins and can be disconnected to minimize supply current consumption in sleep mode.