Difference between revisions of "Team:UMaryland/Design"

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  <p>After construction of the can based cover we tried PCR once more and still found that the reaction did not occur. We assumed that the heat sensor might have been an issue,; the sensor was exposed to the convected air and was relaying information about the air temperature instead of the temperature inside of the PCR tubes. This meant that our feedback system was not accurately responding and controlling the temperature inside of the PCR tubes. Assuming the temperatures inside the machine were not representative of the temperatures inside the PCR tubes, we put the heat sensor inside a PCR tube with mineral oil and placed this inside one of the holes. We ran another PCR reaction, ran the products on a gel and saw a large band of the correct size, indicating that CHIP worked.
 
  <p>After construction of the can based cover we tried PCR once more and still found that the reaction did not occur. We assumed that the heat sensor might have been an issue,; the sensor was exposed to the convected air and was relaying information about the air temperature instead of the temperature inside of the PCR tubes. This meant that our feedback system was not accurately responding and controlling the temperature inside of the PCR tubes. Assuming the temperatures inside the machine were not representative of the temperatures inside the PCR tubes, we put the heat sensor inside a PCR tube with mineral oil and placed this inside one of the holes. We ran another PCR reaction, ran the products on a gel and saw a large band of the correct size, indicating that CHIP worked.
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Hardware
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The working internals of our PCR machine are comprised of hairdryer elements. With the exception of the hairdryers outer housing, the thermal fuse and bimetallic circuit breaker all other working components remain intact. The thermal fuse and bimetallic circuit breaker were shorted using copper wire in order to reach temperatures up to 95 within our machine. The outer plastic housing of the hairdryer was also removed to enable our machine to stand upright and fit PCR tubes. The hairdryers heating mechanism which utilizes a bank of nichrome wires and fan that distributes the heat remained untouched.
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The electronics of the machine are mainly comprised of two relays, an Arduino micro-controller and a lm35 temperature sensor.
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Actuation
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The relays convert the low wattage outputs of the Arduino into a high wattage output needed to power the hairdryer. The relays are switches that can be triggered by the milliwatt output of the Arduino and can handle the 1.8 kilowatt power of the hairdryer.
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Sensing
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The lm35 temperature sensor is used to provide the Arduino controller with input on the current temperature of the machine.   
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Software
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Closing the loop
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  With both the temperature sensor and the relays we are able to provide the micro-controller with the ability to regulate and cycle the machine at various temperatures. To allow for tight temperature regulation within the machine a proportional integral derivative control scheme was adopted. This scheme enable the controller to take temperature reading and calculate rate at which the temperature is increasing, the constant error of the machine found through the integral term, and the proportional error which compares current temperature to a set point. The way our code is designed and implemented utilizes three setpoints, 95,70, and 50 degrees C, all of these are variable and able to be adjusted but for convince we will define the three with these set of temperature values. A any given time only one of these setpoints is active, and the PID control scheme regulates temperature at that specific value. Since the machine need to cycle an hit at least 3 different temperatures our code also logs time after each setpoint is hit, thus allowing us to define a time interval after which the setpoint is altered. What this means is that if we define the first setpoint to be 95 degrees C that our code will execute and tell the machine to heat to 95 and once that temperature is reached it will trigger a timing function which after a defined period will reset the setpoint to 50 degrees which will then force the machine to cool down to the new setpoint.                 
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<img src="https://static.igem.org/mediawiki/2015/5/5a/IGEM_2015_PCR_wire_schematic.png" style="width:800px;height:588px;">
 
<img src="https://static.igem.org/mediawiki/2015/5/5a/IGEM_2015_PCR_wire_schematic.png" style="width:800px;height:588px;">

Revision as of 01:42, 18 September 2015