Abstract:
This project involves wireless communication using the Near Field
Communication (NFC) specification in order to facilitate the monitoring of pulse rates for
small laboratory animals by researchers. We did not test the project on animals due to
the associated protocols, instead we only tested it on ourselves with the knowledge that
this was not a true medical device. The transmitter, which would be attached to the
laboratory animal, consists of an Atmel ATTiny25 Microcontroller (MCU) which reads
an electrocardiogram (EKG) signal from the monitored subject into its analog-to-digital
converter (ADC) and encodes the data with a 106 kHz clock using a Manchester
encoding scheme, as per the IEEE 802.3 standard. The signal is then amplitude
modulated with a 13.5 MHz carrier wave and outputted to a small loop antenna
resonating at 13.56MHz, as per the NFC specification. The use of the MCU enables
smart power management, since the oscillator is enabled by the MCU and the MCU is
powered down except during transmission bursts. The receiver circuitry has a separate
small loop antenna resonating at 13.56 MHz which receives this signal, amplifies it,
demodulates it, and decodes it. Then the resulting data signal is read into the ADC of an
Atmel Mega32 MCU which will transmit that data via serial communication (RS232) to a
PC. A MATLAB software script running on the PC will read the incoming data from the
serial port and output it in a user-friendly manner. The project was mostly successful.
The only pursued specification of NFC that was omitted was the Manchester encoding
scheme, due to problems with clock recovery using a phase-locked loop (PLL).
Full Report (PDF)
Source code (ZIP)