Heart Rate Monitor
• The purpose of this project is to design a heart rate monitor which enables the user to view his/her heart rate on a computer.
• The project included two aspects: Physical Implementation and Circuit Design
• Physical implementation: low cost instrumentation amplifier, band pass filter and an Arduino Uno.
• Circuit Design: cadence was used to design and verify the proper functionality of the analog circuits.
• Goal: designing a low-power version of the actual analog implementation with the aim of miniaturizing the system.
• We used AMI 06 technology, where the minimum allowed length of a MOSFET transistor was 600 nm and the minimum allowed width was 1.5 μm.
•The small electrical signal from the heart generates a common-mode voltage and noise in the system . The signals from the heart are too small and thus it is necessary to amplify the signal and reduce the common-mode voltage.
• An analog circuit with a high gain and low cutoff filter frequency is necessary to condition this signal . A differential amplifier is needed which can cancel out the common-mode signal and amplify the differential input signal.
• An instrumentation amplifier was built using the EL8172FSZ chip to amplify the input signals that the chip would receive through pins 2 and 3. VCC is set to 5 V.
• A function generator was used to give a differential input signal of 1mV at 1Hz imitating the signal coming from heart.
• This output signal is passed into a band-pass filter of 0.5-150 Hz frequency range, which helps to retain only the desired frequency range of the heart’s signal. A band-pass filter using inverting op-amp configuration was built using a 741 op-amp chip.
• This output then gets fed into the Arduino Uno for digitization.
Conclusion and Future Work
• Successfully implemented a heart-rate monitor using off-the-shelf components.
• Successfully designed and simulated the analog part of the system (instrumentation amplifier and the band pass filter) at the transistor level in AMI-06 Technology using Cadence. The amplified and filtered signal from this chip can then be fed to Arduino for digitization.
• The next step for this project is to develop a portable system: wirelessly communicate the digitized signal from an XBee Shield mounted on an Arduino Uno to another XBee Shield that can be connected to an LCD screen.
• In addition, Android/iOS based applications can be developed for the portable system to enable remote monitoring of the heart rate.