Future Work
Currently, the project is in between the design and build phase. The current design will be assembled and tested during the fall semester of 2014. In addition, all firmware and end user interface programming will take place then.
Schedule
There are 15 weeks in the fall semester; however, only 11 will be scheduled. This is to ensure the project is done on time for the final design fair. The first week will be reserved for assembling parts. The first two weeks will be used for initial software programming and stage 1 assembly. Stage 2 and additional programming will take the next two weeks. Six weeks will be reserved for stage 3 PCB assembly and final programming and testing. The remainder of time before the design fair will be used for reporting and presentation purposes.
Prototyping
Prototyping will take place in three stages. This will take the device from initial breadboarding all the way through programming and PCB fabrication. Each stage will perform specific tests and differing levels of prefabricated subsystems. These stages are:
- Stage 1
- Assemble custom circuit components on solder-less breadboard
- Use dev. kits and eval. boards where available
- Run all tests
- Stage 2
- Assemble custom circuit components on permanent prototype board
- Use power supply eval. board.
- Place MCU directly on board
- Verify increased performance due to more permanent connections
- Stage 3
- Design and print PCB with entire circuit onboard
- Do not use any dev. kits or eval. boards
- Rerun all tests
Preliminary Software Operation
Actual programming of the firware has not be started. However, figure 1 shows the overview of how the firmware will operate. This flowchart starts in sleep mode with the smaRTClock running, goes through the sensing and transmission process, and then returns the MCU to its sleep mode. The onboard temperature sensor is used along with a correction factor to increase accuracy. In addition, fault detection is integrated into the data encoding process.
Device Testing
Multiple tests will be performed during each stage of prototyping. These tests are design to test the performance and operation of each susbystem in the device.
- Measure supply current out of battery pack
- Sleep current
- Worst case active load
- Ensure life time greater than 5 years
- Measure DC/DC boost output ripple
- Ensure in tolerance with sensor requirements
- Verify proper conversion of sensor current to ADC voltage
- Measure sensor current with laboratory DMM
- Verify 95% accuracy
- From sensor current to I2C packet
- Test LPF surround current sense amp
- Use noise source
- Use spectrum analyzer to inspect LPF response
- Test TVS diodes
- Connect ammeter in series with TVS diode
- Vary voltage across TVS diode
- Test line filter
- Connect common mode noise source
- Compare input and output spectral response
Manufacturing
The process of final production is not included in this project. However, several concerns will need to be addressed at the time of manufacturing. The PCB may require test pins. These could be used for an external test power supply and connections to verify properation. In addition, the certifications need to be obtained to ensure safe operation in explosive environments.