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20.109(F10): Mod 2 Day 3 Tools for system engineering: Difference between revisions
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20.109(F10): Mod 2 Day 3 Tools for system engineering (view source)
Revision as of 13:10, 4 October 2010
, 4 October 2010→Part 4: Modeling biological versus electrical devices
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===Part 4: Modeling biological versus electrical devices=== | ===Part 4: Modeling biological versus electrical devices=== | ||
In this section, we'll explore the issue of signal strength in the context of an electrical circuit. As you work through this exercise, consider how the lessons learned from experimenting with an electronic circuit would map to the engineering of biological systems. | In this section, we'll explore the issue of signal strength in the context of an electrical circuit. As you work through this exercise, consider how the lessons learned from experimenting with an electronic circuit would map to the engineering of biological systems. You will be given a kit to construct this circuit. | ||
[[Image:PhotoElectronics.jpg|thumb|left|250px|'''starting kit''']] | |||
====Acknowledgements==== | ====Acknowledgements==== | ||
Many thanks to [[Tom Knight]], [[Reshma Shetty]] and [[Barry Canton]] who motivated and designed an early version of this exercise. And a special shout out to Steve Wasserman for his guidance in redeveloping, troubleshooting and building this circuit to more directly reflect the experiment we're performing. | Many thanks to [[Tom Knight]], [[Reshma Shetty]] and [[Barry Canton]] who motivated and designed an early version of this exercise. And a special shout out to Steve Wasserman for his guidance in redeveloping, troubleshooting and building this circuit to more directly reflect the experiment we're performing. | ||
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When you connect the battery to the breadboard, make sure you do so in the correct orientation for the circuit (red to red, black to ground) or the OpAmp will break...really. | When you connect the battery to the breadboard, make sure you do so in the correct orientation for the circuit (red to red, black to ground) or the OpAmp will break...really. | ||
====System design==== | ====System design==== | ||
[[Image:RevisedCircuitDiagram BactPhoto.png|thumb| | [[Image:RevisedCircuitDiagram BactPhoto.png|thumb|center|400px|'''A diagram of the electrical circuit that is analogous to the bacterial photography system.''' Circuit designed by Steve Wasserman]] | ||
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This system is fairly simple one since it only consists of a few components. In contrast to the bacterial photography system in which the signal is propagated through protein activities, here signals are propagated as either voltage or current. As you can see in the schematic, the circuit contains the following parts. | This system is fairly simple one since it only consists of a few components. In contrast to the bacterial photography system in which the signal is propagated through protein activities, here signals are propagated as either voltage or current. As you can see in the schematic, the circuit contains the following parts. | ||
#[[Media:Photodiode SpecSheet.pdf| Photodiode]]: #LT959X-91-0125: a light sensor ''(mimics Cph8 and the phycobilins)''. When light shines on the photodiode, its resistance is decreased and current flows through it. | #[[Media:Photodiode SpecSheet.pdf| Photodiode]]: #LT959X-91-0125: a light sensor ''(mimics Cph8 and the phycobilins)''. When light shines on the photodiode, its resistance is decreased and current flows through it. | ||
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#[http://www.breakup.de/resources/resistor.html Resistor]: components which resists current flow by producing a voltage drop across it. The gain in this system is proportional to the resistance, and by varying the resistance into the OpAmp, the sensitivity of the circuit to light can be tuned. | #[http://www.breakup.de/resources/resistor.html Resistor]: components which resists current flow by producing a voltage drop across it. The gain in this system is proportional to the resistance, and by varying the resistance into the OpAmp, the sensitivity of the circuit to light can be tuned. | ||
#[http://www.allelectronics.com/make-a-store/item/LED-2/GREEN-5MM-T1-3/4-LED//1.html LED]: a device with a detectable output ''(mimics LacZ)''. A voltage drop across its terminals turns the green-colored light on. The 820Ω resistor is added to the circuit before the LED to ensure that the voltage drop across the LED isn't too high (which can cause the LED to breakdown).<br> | #[http://www.allelectronics.com/make-a-store/item/LED-2/GREEN-5MM-T1-3/4-LED//1.html LED]: a device with a detectable output ''(mimics LacZ)''. A voltage drop across its terminals turns the green-colored light on. The 820Ω resistor is added to the circuit before the LED to ensure that the voltage drop across the LED isn't too high (which can cause the LED to breakdown).<br> | ||
===Let's start building=== | ===Let's start building=== | ||
