Team Vision for System-Level Design Phase
At the beginning of this phase, our team planned:
- To fully justify why an environmental test chamber would be most practical
- To figure out how to introduce a "Biochar house" into the test rig
- To determine the best type of micro controller, battery, and data storage device
- To generate the best ways to control and adjust heat, cold air, and humidity
During this phase, our team generated multiple concepts:
- A cube form of the "Biochar house" would be the most suitable set up
- How to properly position temperature probes
- Which system would best work to control the humidity in the test chamber
The figure above is a flow chart of all functions and sub functions as clarified by customer and engineering requirements.
As the main goal of this project is to test Biochar as a housing material and compare it to standard housing materials, we must be able to access Biochar, run appropriate tests on the Biochar to determine its insulating and humidity controlling abilities, and lastly to analyze the data acquired from the tests.
Part of accessing Biochar requires that we make into a suitable housing material, however we choose to do so. After that happens, the material must be able to secured to the test chamber that we decide to implement. Further, after the material is secured, multiple tests have to run to characterize the materials. This is two pronged, one of which is to record the change in temperature and humidity utilizing a dry wall as well as a wet wall. Lastly, once an appropriate number of tests were run, a data storage device used in the test chamber can then be retracted and analyzed in Excel.
Potential Failure Modes
Anticipated potential failure modes:
- Supply of Biochar delayed
- "Recipe" of Biochar building material not sufficient
- Breakdown of test rig or subsystems
- Ease of change and use
- Loss of data
- Wet wall does not perform as expected
The above chart is a simple illustration of other environmental test chambers compared to our concept. While the two initial designs already established lack in areas such as being self powered and data recording, our design will incorporate all areas that deem most appropriate and will be unique.
Morphological Chart and Concept Development
Pugh Chart and Concept Screening
- Ease of use and application
- Accuracy and reliability
- Ability to withstand any condition and climate
- Ease of manufacture and attainability
From the above screening, the following concepts were selected as systems of the test rig:
Access Material: Drawers. A drawer is a
more practical method to expose the test sample to
Sense Data: We are going to chose
sensors that provide necessary accuracy, recording
capability, and that are more practical in size and
weight in relation to our test rig.
Store Data: USB storage. This method
because it is the most common and most availability, and
least likely to have compatibility issues with users'
Secure Material: Clamp. Most practical
economically and easiest to use
Airflow: Fan. Lightweight, efficient,
cheap and readily available.
Change Temperature: AC Compressor and
Electric Coil. For the electric coil, it allows increase
in temperature without changing the humidity. For the AC
Compressor, it is the quickest to decrease temperature.
The AC Compressor also dehumidifies.
Change Humidity: Ultrasonic humidifier.
You can introduce humidity without introducing heat.
Analyze Data: Graphical Spreadsheet. It
allows for quick analysis, but also contains the detail.
Deep analysis using everyday comfortable using
User Interface: LCD Controller. It is
the easiest and cheapest to implement.
Power Supply: AC Power/Battery. Ac Power will allow us to do extended testing. And battery powered will allow to do remote location testing in ambient conditions.
Feasibility: Prototyping, Analysis, Simulation
Is the MSP430F6xx a feasible controller option?
Minimal Power Consumption
- The temperature controlling devices (heating coil, A/C compressor) will account for the vast majority of power usage. The microcontroller power consumption becomes essentially negligible.
- MSP430F6xx power consumption
- Active Mode (sampling, user interaction, etc) 25 mW * .02
- Standby Mode 12.5 uW * .98
- Max Expected Test Time 168 hrs
- Total Power Consumption .086 W*hr
- Likely Battery is 35 W*hr
MSP430F6xx is sufficient
- There are 6 analog sensors that will be sampled on the output of internal ADCs on the MSP430F6xx. By using 8 bit floating point numbers the sensitivity will be within the error of the sensors. A minimum sampling rate will be 60 seconds. The code is expected to require less than 200 kB.
- Sample Size * Samples/hr * Time + Code
- 6 Bytes * 60 * 168 hr + 200 kB
- Total memory required >> ~262 kB
- MSP430FX5 has 512 kB
MSP430F6xx is sufficient
- The total budget is $500. The test chamber donation
leaves us in good shape to purchase a higher performance
microcontroller. Although this is not necessary, a
quality controller greatly reduces the possibility of
time consuming problems later in the project schedule.
- The MSP430F6xx with development kit $55 - $75
MSP430FX5 is sufficient
I/O Ports Required
- The system will require inputs for the sensors and user interface buttons.
- The system will require outputs for condition
controls and indicator lights.
- Inputs >> Int/Ext/Amb Temp, Int/Ext/Amb Humidity, Keypad
- Outputs >> heat element, A/C compressor, wet wall pump, humidifier valve, 2 indicator lights (red, green)
- Total gpio count is 14
- MSP430FX5 has 74 assignable pins
MSP430FX5 is sufficient
- Since there are 6 analog sensors being used, a
controller with at least that many ADCs will be required
to avoid having to add an external one which would also
require additional pins.
- MSP430FX5 has 16 on board ADCs
MSP430FX5 is sufficient
Question: How will the test rig maintain self-powered stability?
- The test rig will run continuously, collecting data every 5 or 10 minutes.
- Battery will be probably small in size, considering the size of the test rig.
- The source of power should be able to keep all equipment running, even all at the same time.
- 12V golf cart battery of 35 Amp/hr: 420W of power
Runtime will be 180 minutes (3 hours), and should accommodate tests every 5 minutes (36 times) or 10 minutes (18 times).
- What equipment are we using?->Sum the power requirements of all the equipments
- Still no finalized schematic
- what amount of power will we be using?
- What components are present?
- Research what power sources to use:
- Car batteries? -> Enough power?
- Solar Cells? -> Budget?
- Fuel Cells?-> Budget?
- Space for power source: -> Weight of the test rig affected?
- Adequate wiring to power source/equipment?
Designs and Flowcharts
The above flow chart lays out different inputs and outputs associated with the design. Starting with the computer, the user will input values, a power source will initiate a power supply and the temperature and humidity sensors will begin to sense and measure. The user and sensor inputs send data to the controller, while the power supply sends power. From the controller, tests are run to increase and decrease temperature and humidity as so for appropriate tests. Lastly, the controller will send the following data back to the computer to output results.
Plans for next phase
For the next review, we will have all of our concepts at system and subsystem levels finalized. We will also have a drawn up schematics of our full system, including subsystems to effectively communicate our overall goal and concept. On top of all of this we will have done multiple feasibility analyses, a bill of materials, and another risk assessment.