Final Project - Heart Monitor - ECE 210 Final Project...

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ECE 210 Final Project Report May 4, 2004 Eric Brumer Albert Ho
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Introduction The object of our design project was to build and test an electronic heart rate monitor. This device would generate an audible tone every time the heart beats. The system consists of a photo-transducer for human interface input, a circuit to process the signal produced by the photo-transducer, and finally an audio output for hearing the subject’s heart rate. From an engineering standpoint, our design is split into many components that perform a certain function for our circuit. The first component is our pulse detector circuit , which contains the photo-transducer that directly interfaces with the patient’s skin. The amount of infrared light reflected from the skin is emulated as a signal produced by the photo-transducer, which in turn shows the heart’s pulse. The photo- transducer provides us with an extremely weak noisy signal that is then sent to the band- pass filter , the next component. The band-pass filter is designed to block out DC signals and 60 Hz noise in order to generate a signal that shows much more clearly when a pulse is present. This signal is then sent to a Schmidt trigger , which will produce a square-wave series of high and low signals. When a pulse is detected, a low signal at -12 V is produced, but otherwise the Schmidt trigger would produce a high +12 V output. Our gating circuit then takes this square-wave and allows a high frequency output generated from an oscillator circuit to propagate if the signal is low. Finally, the high frequency signal is sent to our audio amplifier circuit , which is designed to amplify the current needed to allow an audible tone to be generated in a speaker. The integration of all these parts is shown in the block diagram on the following page. 1
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Electrocardiogram Block Diagram The following is a flow chart of our circuit. The blocks represent circuit systems which will be analyzed in depth later. The arrows represent the way in which the signal travels, and the text describes what the signal looks like as it progresses through the circuit. The next page contains the complete circuit diagram. 2
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Pulse Detector Circuit This is the first system in the device. The spec sheet of the diode labeled Diode 1 says that its operating range is in between 20mA and 40mA. We are also told that the voltage drop across the diode is 1.6V. Attempting to make the current through the resistor R equal to 20mA, we have, by Ohm’s law: The region in the rectangle is a photo transducer, which will turn a light pulse into a voltage pulse. When we placed our finger on the device, the voltage at point 3 dropped from 4.16V to 3.75V. The pulses of blood passing through the capillaries in our fingers will cause a signal to be generated at point 3. The signal is too weak to be visible, so we
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This note was uploaded on 09/26/2007 for the course ECE 2100 taught by Professor Kelley/seyler during the Spring '05 term at Cornell University (Engineering School).

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Final Project - Heart Monitor - ECE 210 Final Project...

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