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Beta Prototype
Beta Prototype
- Even with challenges of COVID-19, beta prototype was assembled with key improvements over the alpha prototype.
- Each of the major improvements stated previously are broken down in further detail below in this section. The figure aside shows what the beta prototype system looks like after putting together all the individual components.
Component Selection
Component Selection
Valves
Valves
The team’s selection process for the solenoid release valve required in the system is detailed below. The team would have continued with purchasing but due to the additional electronic components required for valve actuation, and limiting vendor supply, manual release valves were used for this iteration of the prototype.
- The solenoid valve selected had to be available for purchase through one of the approved vendors.
- Important valve specifications included applied voltage, port dimensions (to accomodate selected tubing), and normally open/closed condition.
- 12V, 1/8“ port size, normally open valve specifications were selected.
- 12V actuated solenoid valves were found to have the lowest applied voltages needed of any valves researched. This would be the most attainable voltage supply for the DAQ system used, Arduino or Raspberry Pi, as these systems normally operate around 6V but can be amplified slightly using additional electronic components.
- 1/8“ port size was selected because it was closest to the dimensions of the pump tubing (2mm ID x 3mm OD). Additional 11/64” x 3/32” barbed adapters would be purchased that would screw into the valve ports and which the tubing would then be fitted over, creating a seal (3/32” is slightly larger in size than the 2mm ID of the tubing causing a slight interference fit to best prevent air leakage).
- Normally-open condition was selected for safety concerns. This would require the valve to be actuated (energized) in order to close and seal the system. In the event that the system malfunctions and the valve cannot be energized, it will return to its open position preventing unwanted adherence to the patient. A normally closed valve would remain in contact with the patient if not energized to open, potentially leading to patient injury if adhered for too long.
- 12V, 1/8“ port size, normally open valve specifications were selected.
Peristaltic Pump
Peristaltic Pump
- For beta prototype, a new and improved peristaltic pump was ordered.
- Pump was capable of a flow rate of 0.4 to 84 mL/min or an engine rpm of 0 to 150.
- Pump has a digital display that can be toggled to show rpm or flow rate and has accuracy within .2mL/min.
- This new pump will allow for the team to put validity behind testing, and assign specific flow rates to negative pressure cavity measurements. This is critical when attempting to mechanically characterize the skin.
- Pump is currently on purchase order and should be acquired within the next two weeks due to COVID-19 complications.
Pressure Sensor Integration
Pressure Sensor Integration
- For the beta prototype, two pressure sensors were implemented.
- These sensors communicate over the I2C bus and have the same address making it difficult to read data from two sensors at a time.
- A multiplexer was used in order to solve this issue.
- The multiplexer can expand the capabilities of the I2C bus by creating multiple channels to send and receive information through thus being able to read pressure values from both sensors simultaneously.
- The implementation of this multiplexer in the Beta prototype helped to develop the intended system where two pressure values can be read and analyzed through the DAQ.
Wiring Schematic for beta prototype
Data Acquisition Unit - Raspberry Pi
Data Acquisition Unit - Raspberry Pi
- One of the major improvements in prototyping came from the switch to Raspberry Pi and in the revision of the code which can be found in the supporting document.
- The switch from Arduino to Raspberry Pi meant coding the project in a different language.
- Arduino uses C/C++ while the Raspberry Pi uses Python
- Using a Raspberry Pi can utilize endless repositories including ones to communicate with multiple sensors over the same I2C bus and create a graphical representation of the data and save the data later in a file.
- Being able to save the data and communicate with more than one sensor was something that was not able to be accomplished on an Arduino.
- Figure 5 below outlines the wiring diagram developed during Phase 5 and what is implemented in the Beta prototype.
Cup Integration
Cup Integration
- The existing cup manufactured during the Alpha prototype was integrated into the overall system for the Beta prototype.
- One tube was inserted in the side hole and connected to pressure sensors 2 while the other tube was connected through the port on top leading to a T-adapter that split to pressure sensor 1 and the rest of the system. This can be seen in Figure 3 above of the Beta prototype system that was assembled.
- During phase 5, more cups were intended to be manufactured, but due to COVID-19 this was not realized since the Stevens Machine Shop was closed.
- The plan was to include an adapter on the side hole just like the top of the cup had to easily connect tubing to it.
- Another design that was intended to be manufactured included adding metal inserts instead of the current plastic ones
- This would allow for an easily manufactured connector piece instead of the stepped design from Phase 4 which proved difficult to manufacture properly and this new design can be seen in Figure 6 below.
- Although a new design was not fabricated, the existing manufactured cup still functioned as intended and was used in the Beta prototype system.
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