BioBuilding: Synthetic Biology for Students: Lab 3 --Electronics: Difference between revisions
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[[PDF of this page]] | [[Media:BioBuilding Students Lab3 Electronics.pdf| PDF of this page]] | ||
=Lab 3: Picture this= | =Lab 3: Picture this= | ||
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*The resistor is needed to limit the current through the LED. Too much current can damage it. The LEDs in this kit are strong enough that they won't burn out instantly if you connect them straight across the battery, but using a resistor is still recommended. | *The resistor is needed to limit the current through the LED. Too much current can damage it. The LEDs in this kit are strong enough that they won't burn out instantly if you connect them straight across the battery, but using a resistor is still recommended. | ||
*You could also put the resistor on the power side and the LED on the ground side; it makes no difference. | *You could also put the resistor on the power side and the LED on the ground side; it makes no difference. | ||
===Building the bacterial photography circuit=== | ===Building the bacterial photography circuit=== | ||
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#Double check your connections with the circuit diagram above before you power it up. | #Double check your connections with the circuit diagram above before you power it up. | ||
#Test your circuit by shining a light on the photodiode and seeing if the LED responds. | #Test your circuit by shining a light on the photodiode and seeing if the LED responds. | ||
====Putting it all together==== | |||
*Explain the role each component plays in the electronic circuit. Which part of the biological circuit does each represent? | |||
*No doubt, building this circuit was quicker and easier than actually assembling a biological circuit -- for example, you didn't have to wait for bacteria to grow, or spend time cutting and pasting wires the way you would cut and paste DNA to make a functional plasmid. What are some traits of these components, of the breadboard, or of electronics in general, that make electrical engineering easy in this way? | |||
*Every analogy has limitations. What are the limitations of the circuit you built as a model of the bacterial photography system? What could you do to make it more realistic? | |||
===Examining system behavior at different gain values=== | |||
'''<font color = purple>If your teacher specifies, continue to this exercise for exploring gain. You may be asked to answer the questions associated with each section.</font color><br><br>''' | |||
A circuit with very tight fully-on-or-fully-off behavior is more "digital", or switch-like, while a circuit where the LED can have a wide middle range of brightness is more "analog", or dial-like. The range of flashlight intensities that can hold the LED half-lit is a measure of the ''gain'' or strength of the amplifier. More precisely, the gain is the slope of the LED-output-vs.-photodiode-input line. Because the ''maximum'' brightness is the same for every circuit, a high-gain amplifier will cause the LED's brightness to max out even at a low level of input to the photodiode, whereas a low-gain amplifier will cause the LED's brightness to increase slowly before maxing out, as the photodiode input increases. We can ''tune'' this gain by changing the value of the gain resistor. | |||
=====Initial Condition: Resistance = 10 MΩ===== | |||
Right now, the OpAmp's output and minus input are connected with a 10 MΩ resistor. | |||
#What happens to the LED when you power up the circuit? | |||
#What happens to the LED when you shine the flashlight on the photodiode? | |||
#Can you get the LED to hold steady at 1/2 its maximal brightness, by moving the flashlight farther away, shading it, etc? | |||
#Sketch a graph with flashlight intensity on the x-axis and LED light intensity on the y-axis. At infinite resistance in place, is the circuit's behavior better described as a switch or a dial? | |||
=====Modification: Resistance = 0Ω===== | |||
Replace the 10MΩ resistor with a wire. | |||
#What happens to the LED when you power up the circuit? | |||
#What happens to the LED when you shine the flashlight on the photodiode? | |||
#Can you get the LED to hold steady at 1/2 its maximal brightness? | |||
#Add a line for this circuit to your graph. Is this circuit's behavior better described as a switch or a dial? | |||
=====Alternative: Resistance = infinite Ω ===== | |||
Remove the wire connecting the OpAmp's output to its negative input. | |||
#What happens to the LED when you power up the circuit? | |||
#What happens to the LED when you shine the flashlight on the photodiode? | |||
#Can you get the LED to hold steady at 1/2 its maximal brightness? | |||
#Add one last line to your graph. Is this circuit's behavior better described as a switch or a dial? | |||
====Putting it all together==== | |||
* How does this relate to the end of the computer simulation exercise, when you tuned the system with sliders? | |||
* When might you want switch-like behavior in a biological system, and when might you want dial-like behavior? | |||
* What are some everyday examples of switch-like and dial-like systems? What element or aspect plays the role of "gain" in each one? | |||
==Data Sharing== | |||
When you've finished your work on this part of the activity, upload your data to the link on the BioBuilder site that's [http://www.biobuilder-submitdata.org/users/login here.] You'll be able to compare what you've done to what other BioBuilders around the country have tried. | |||
==Navigation== | ==Navigation== | ||
*[[BioBuilding: Synthetic Biology for Students]] | *[[BioBuilding: Synthetic Biology for Students]] |
Latest revision as of 07:32, 18 January 2012
Eau That Smell Lab |
Lab 3: Picture thisExplore an engineered biological system through a computer simulation, an electronics building kit, and a real-life example.
Part II. Electronic vs Biological CircuitsIn this activity, we'll explore signaling 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. SafetySafety for you: Safety for the circuit components:
System designThis system is a fairly simple one, consisting of only 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. When light hits the photodiode, it generates a current signal. The OpAmp takes in this current signal and produces a voltage, which signals the LED to produce light. As you can see in the schematic, the circuit contains the following parts:
Introduction to BreadboardsYou will be building this circuit on a breadboard, which is a much cleaner way to construct circuits than just wiring everything together. Start by building a very simple, "Hello World" circuit to understand intuitively how breadboarding works. (If you have used a breadboard before, feel free to skip this section.) Take a look at the rows of holes on your breadboard. In the middle, the holes are arranged in short rows of five. The five holes in each row are all connected to each other (via thin strips of metal inside the breadboard). On the sides are the rails, or long rows of holes marked with red or blue lines and a plus or minus sign. All the holes in a rail are connected to each other. Rails allow you to conveniently serve power/ground to many locations at once. For example:
Hooking up an LED
A few hints:
Building the bacterial photography circuit
Putting it all together
Examining system behavior at different gain valuesIf your teacher specifies, continue to this exercise for exploring gain. You may be asked to answer the questions associated with each section. Initial Condition: Resistance = 10 MΩRight now, the OpAmp's output and minus input are connected with a 10 MΩ resistor.
Modification: Resistance = 0ΩReplace the 10MΩ resistor with a wire.
Alternative: Resistance = infinite ΩRemove the wire connecting the OpAmp's output to its negative input.
Putting it all together
Data SharingWhen you've finished your work on this part of the activity, upload your data to the link on the BioBuilder site that's here. You'll be able to compare what you've done to what other BioBuilders around the country have tried.
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