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Detailed Design

Table of Contents 1 Team Vision for Detailed Design Phase 2 Progress Report 3 Drawings, Schematics, Flow Charts, Simulations 3.1 Switch Prototype 3.2 Switch Prototype Mechanical Drawings 3.3 Medical Impact Study 3.4 Switch Prototype Schematics 3.4.1 Interface 3.4.2 MicroController 3.4.3 Power Management 3.4.4 IMU 3.4.5 Switches 3.5 Switch Prototype PCB Design 3.6 Prototype Software Design 4 Bill of Material (BOM) 5 Risk Assessment 6 Design Review Materials 7 Plans for next phase

Team Vision for Detailed Design Phase

Team Goals:

• Integrate IMU
• Begin software design to allow full-alphabet typing
• Fix Bluetooth connection issues
• Determine final design and parameters for Senior Design Phase II
• Begin ordering parts for prototype build
• Complete testing on alternative sensors
• Construct engineering and electrical drawings/schematics
• Review Customer Requirements, Engineering Requirements, and Risk Management Chart to check for any updates

Team Accomplishments:

• Created Functional Switch Prototype
• Parts were ordered for Switch prototype testing
• BOM was updated for Senior Design Phase II
• Preliminary schedule was drafted for Senior Design Phase II

Progress Report

In the past couple weeks we have accomplished :

• Created a working non-wearable prototype
• Drafted a PCB design
• Discussed methods for manufacturing various parts
• Identified all parts to create drawings for.

Here is what we intend to accomplish in the week leading up to the DDR:

• Complete engineering drawings for the main components of the system
• Have a firm understanding of the remaining parts
• Make decisions on materials and manufacturing processes to begin construction with
• Complete draft of PCB design

Here is what we would like to accomplish, but will likely not complete before the review:

• Complete ALL engineering drawings
• Finalize PCB
• Completed test plans for Engineering Requirements
• Simulations with various materials to select ideal manufacturing materials
• Complete qualitative feasibility testing on 3-axis Hall Effect and TOF Sensors

Drawings, Schematics, Flow Charts, Simulations

This Design architecture represents the functionality that will be used by the prototypes developed and tested by the DEXT team.

3-Axis Hall Effect and TOF sensor prototypes are on hold while the code and functionality of the Switch prototype are being developed and tested.

Switch Prototype

Currently Functional:

• Non-wearable 4 button interface
• 4 states / 4 button sets / 4 letters per button set
• 16 letter characters available
• Stable connection on android only

Future Goals:

• Wearable design (Including chassis and battery)
• Multi-press characters (increase # of characters per state to 9 from 4)
• All letter characters & useful special characters available
• Haptic Feedback
• Stable connection on all platforms (IOS, Android, Windows, MacOS)

Current State:

• Breadboard mounted uC and IMU with detached interface
• Requires external power
• Can pair with android devices
• Can determine its orientation (Up, down, left right)
• 1 letter per button per orientation, 16 letters a-p

Switch Prototype Mechanical Drawings

Prototype can also be made with separate housings for each button, connected to each other with wires. Pros:

• More flexible, so possibly more comfortable
• Could improve adjustabilility

Potential drawbacks:

• Could be irritating to wear if it moves too much
• Wires are less durable than casings

Watch-style straps encasing wires connect top and bottom components, with a buckle or velcro strap to adjust size (like a watch). Design can explore stacking the PCBs in a single case to make it more compact.

The folder containing the Solidworks CAD documents can be found here.

Medical Impact Study

Forces acting on the arm:

• N = Contact with the humerus at the shoulder articulation
• F = Force that supports the arm (deltoid muscle)
• Sum of Fx = 0 , Sum of Fy = 0
• -FCos15 + Nx = 0 → Nx = FCos15
• FSin15 - W - Ny = 0 → Ny = (FSin15 - W)
• Torque of F = 12 * F * Sin15 → 12FSin15 = 30 *44
• Torque of W = 30 * 44 →
• F = 120/Sin15 N
• Angle = 15 degrees
• N = { Nx = 120 Cot15 N; Ny = 66N }

Switch Prototype Schematics

Interface

A micro USB type B connector is used in conjunction with a CP2102 USB-UART bridge to program the ESP32 over UART. Additionally, a couple transistors are used to hold IO0 and EN low during programming to enable bootloader mode on the ESP32.

MicroController

The ESP32 has connections to four buttons, an I2C bus for the accelerometer, three LEDs that can be used for status or debugging, and one extra GPIO broken out. Buttons with weak pull-ups and strong pull-downs are attached to IO0 and EN to program the device in the event the transistor circuit fails to do so.

Power Management

A Texas Instruments single lithium Ion cell charger is used according to the datasheet, with resistors in place to set a safe charging current and to disable the thermocouple support. LEDs are used to indicate charging status and power supply adequacy.

The AP9101c measures for over and under-voltage statuses on the single lithium ion cell. It disconnects a common-drain MOSFET pair if the monitoring sees a voltage too high or too low based on the exact model number.

A common 1117 LDO drops the voltage to 3.3V for use by the accelerometer, CP2102, and ESP32. The source of the input voltage can be either USB 5V or the battery voltage, selectable via solder jumper.

IMU

The IMU is connected as according to the open source schematic provided by Adafruit. Some pins are pulled high to enable I2C communication and to set certain configurations in the device.

Switches

A universal footprint is made to hold any of the buttons that are to be tested. Connection to the main board is done through daisy-chaining so that all but one of the wires entering one side of the board as passed through to the opposite side.

Switch Prototype PCB Design

The folder containing the KiCAD documents can be found here.

Prototype Software Design

The current prototype test code can be found here.

Bill of Material (BOM)

This is the current BOM for the components used in the current prototype, switches ordered for testing, and parts for other prototypes yet to be constructed.

Risk Assessment

• Updated Risk Assessment for Design Review

Design Review Materials

Presentations
Problem Definition Presentation
System Level Design Review Presentation
Preliminary Detailed Design Review Presentation
Detailed Design Review Presentation

Plans for next phase

Before next semester, the team needs to finalize the current in progress prototype, reserve rooms for meetings, and update anything that changes as a result of these actions. The team's plans for the next phase can be found here.

Team Member 3-week Plans
Willow
Jon
Nick
Sarah
Tim
Alice
Vincent

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