415.6.rough - BIOE 415 Lab Report 6 Monday Section...

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BIOE 415 Lab Report 6 Monday Section Introduction In this lab, two new circuit elements were introduced: the diode and the transistor. After building and measuring outputs for these simple circuits with these devices, a photoplethysmograph circuit was constructed. This circuit requires the use of the newly introduced diode and a transistor along with previous knowledge of amplifiers. With this circuit, the heart rate can be measured. This is done using an infrared diode, which senses reflected light from a fingertip which varies with changes in blood volume in capillaries due to heart beating. Methods Diode Model Transistor Model
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Photoplethysmograph RESULTS 3.1.2 – LED The voltage across the LED was measured to be 2.049 V. Knowing the source voltage, the voltage across the resistor was found and then the current through it was calculated. This current is the same through the diode and was measured to be .0103 A. 3.1.3 – Turn-On Voltage As the source voltage decreased, the voltage across the diode also diminished. In addition, the light in the LED became dimmer until it eventually turns off at about 2.05 V. The turn-on voltage of the diode was the voltage across the 9V supply, which was 2.049 V. This matched closely to the prelab of 2.2 V. 3.2.2 – Transistor For the source voltage of 1 V, the voltage across the collector was 2.51 V. Dividing by the resistor yields a current through the collector of .00115 A. Voltage across the base was measured to be .460 V. The current through the base was calculated to be about 8 uA. The voltage from base to emitter was
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415.6.rough - BIOE 415 Lab Report 6 Monday Section...

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