Preliminary Detailed Design
Table of Contents
Team Vision for Preliminary Detailed Design PhaseGoals for Preliminary Detailed Design:
- Design electrical subsystems
- Create schematics
- Choose components
- PCB Layout
- Perform prototyping and feasibility analysis on electrical design
- Create software charts / diagrams
- Software Implementation
- Compile BOM
Completed Action Items:
- Created schematics and top level electrical drawings
- Chose components
- Electrical simulations
- Feasibility analysis on electrical designs and components
- Created software flowchart
- Software Implementation of UI
- Compiled BOM
Feasibility: Prototyping, Analysis, Simulation
- Iterative activities:
- Iteration on feasibility issues from previous design review: quantitative measure of requirements/ adding requirements:
1) Issue: "“if you're gonna do 20% can do 8 bits of resolution don’t need 10-bits of resolution”- Customer Dr. Fuller.
- Action: quantify bits and reiterate on resolution: talked to customer wants within 20mV -Created requirement for resolution and quantify.
- Quantify: we have 12 bits using 0-5 using: Voltage / 2^num of bits we find .001221 or 1.2 mV is what we have according to fuller 5 / 2^bits = 20mV would be a good resolution to aim for.
- Solve: Customer now agrees with our selection/ why it was chosen.
2) Issue: How do you quantify how long batteries last and why did you choose rechargeable/ what requirement to back it up:
- Action: Ask on how long will want batteries to last, quantify lifetime and cost with simple calculation. Create requirement for use:
- Quantify: Customer: "One week For disposable batteries would be fine"
- Using TI resource .7W of power is dissipated, we assume 1W for simplicity and to account for error - Compare - 9V alkaline vs Li-ion.
- Typical 9V = 500mAH ~4.5 WH /1 W = 4.5 hours of use.
- Our Li-ion = 3000mAH ~ 11.1 hours of use
- Estimate : TAs or students / customer use tester 15 mins a day.
- This means per week 1 hr 15 mins of use, 9V lasts 3 weeks 4 days, Li-ion lasts 8 weeks 6 days, 9V has 2 uses in one use of Li-ion, and gets disposed.
- Pricing: 9V alkaline = $1.4 * 2 uses = $2.8
- Li-ion good one we assume is $10-15 pick $15
- 15 / 2.8 = 5 uses the Li-ion beats the 9V so in 12 months or a ~year.
- Keep in mind this is just a basic calculation.
- Solve: Have quantified lifetime and price in a simple calculation, create a requirement for battery lifetime to be put in User manual.
3) Customer mention of software and button shut off so will automatically turn off when not in use or have button to turn off at will, this furthers conserve battery life.
- Solve: created Latching Circuit for after charging board, and working on GPIO for reset, Created Requirement for shut off aim for 30 s of non use.
4) 03962A board voltage regulation and turn off needs to be found.
- Solve: Used lab to find output versus input varying 5V -2.8V to the input and found critical values. Generate table for usb input.
- table is made, 5V produces 4.13 V out, less that the max 4.2 V charge
- turn off around 3V and LED chagrin indicator goes off around 4.3 V input
- will test turns off if battery input is below 2.8, battery input parameters - on output voltage drops off near 3V but no auto turn off.
5) Confirm functionality of Mass Interconnect's ability to deliver and measure voltage/current.
- Solve: Designed and simulated Mass Interconnect circuit. Engineering requirements are met.
- To test voltage supplying ability, the DAC voltage is swept across its full range of 0-5 volts and the voltage on the pin is measured.
- Additionally, the ability to supply consistent voltage with a different voltage across the load is tested.
- Finally, the ability to float the pin is tested. These results are graphed as V(uut) on the y-axis vs. V(DAC) on the x-axis, where the UUT is the pin.
- To test the ability to drive negative current, the DAC input is swept from 0-5 volts, and the voltage on the other side of the load is stepped to 0v and 20v.
- This provides a ±20v differential to the load, and allows for the comparison of positive current with negative current.
- From the results, it can be seen that the negative differential voltage can be achieved, and negative current properly flows.
- Finally, maximum current current supply is investigated. To test this, load resistance is stepped, and pin voltage is observed. The maximum supplied current
- occurs when the required 0v-20v range can't be achieved. With a 100 Ohm load, it nearly failed to achieve +20v, while with a 50 Ohm load, it achieved a max of
- 12.5v. This indicates that a maximum of about 200mA may be drawn before non-linear effects appear, and about 250mA may be drawn before required voltages can't be reached.
6.) Confirmed functionality of current sense circuit
- Implemented current sense amplifier MAX4378HAUD in test circuit to ensure proper gain and operation
- Supply voltage was set to 24V, a 10ohm sense resistor and 10kohm load resistor were put in series and the sense resistor voltage was amplified by the amplifier and measured.
- Gain was calculated to be 100 as expected. Supply voltages of 22V and 20V also tested.
- Output voltage of amplifier saturates at 4.24V for Vcc of 5V
- Output voltage offset was ~2mV
Drawings, Schematics, Flow Charts, SimulationsBelow is a top level diagram which displays the signal connections between the microcontroller and major electrical systems.
Below is a schematic for a single portion of the Mass Interconnect system. The actual IC Tester will require 16 of these sub-circuits (one for each pin on the DUT).
Below is a flow chart which describes the main functions of the software to be implemented.
We tested the Nextion 2.8" display to show it would be capable of showing results properly and had the proper customization.
Needed to check 24V output and battery voltage level using GPIO to power system: comparators for this are implemented, one checks the 24V to the measurement and signal portion, the other checks the battery and tell when level is less than 3.125 V input ~20% level (user told to charge battery) Simulation and setup for this: https://edge.rit.edu/edge/P17342/public/Benjamin%20Lane/UnderVoltageDetection-Onlynon-inverting.pdf
Bill of Material (BOM)
- To ensure proper operation of our tester, a small selections of chips with and without known problems should be gathered. Each chip should be run through its respective test and then rechecked by hand to ensure no change occurred. If the tester reports the correct state for each IC, it can be said that the tester is working as it should.
- To test expandability, a current TA should be selected to add an additional IC to the tester. They will be provided all the documentation and materials they need. If they are able to add the IC and perform a test described above within a reasonable amount of time, then the expandability portion of the tester can be said to be functional.
- For user interface testing, a current RIT EE student should be selected and asked to test a number of chips with minimal to no documentation included. The student should be able to operate the tester on intuition alone. If the student can perform a test within a certain amount of time and interpret the results.
- Once a hardware prototype is finished we can perform a power consumption analysis and calculate an expected run time. Ideally this would exceed the customer requirement of 1 week on disposable batteries. The auto off feature should also perform as expected based on a user entered timeout in the UI.
Risk AssessmentUpdated Risk Assessment
Plans for next phase
- As a team, where do you want to be in three weeks at your next review?
- Complete TPS55340 Flyback Converter Simulation
- Test both DC-DC converters in hardware
- Write up from Tests a prototype test plan and implement to verify system
- make changes to parts and order based on tests /update BOM
- GPIO designation for power- comparators for 24V and battery voltage level -check mode and test in hardware
- PCB layout / dimensions with team
- PCB case design and possible test print -final 3D print next semester
- Develop / improve current sense sub-circuit
- Help team with electrical design, prototyping, and documentation
- PCB layout with team
- Mass interconnect prototyping
- PCB layout
- Update BOM
- Model components we are using for PCB design (1-2 hours, 3/31)
- Roughly model case (20 min, 4/7)
- Print out rough model (20 min, 4/7)
- Outline dimensions of PCB (30 min, 4/7)
- Complete beta version of software w/ the following
- Implement configuration file format (4 hours)
- Implement control of external circuitry according to test plans (4 hours)
- Finalize UI design for future expandability (2 hours)
- Prototype 3D printed case design (2 hours)
- PCB Layout
- Complete simulations for the schematics
- PCB Case Design
- Improve the IC tests
- Modify and verify IC tests
- PCB layout
- Assist in the design of the PCB case