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ECE 210 Final Project Report May 4, 2004 Eric Brumer Albert Ho
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IntroductionThe 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 circuitthen takes this square-wave and allows a high frequency output generated from an oscillator circuitto 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