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Goals
- Simplifies inventory management and software, allowing a single core config for all boards
- Simplifies board debugging - isolates issues to either the controller or carrier boards
Background and strategic fit
One of the biggest issues with MSXI's electrical system was its inconsistency in parts and pinouts. There were at least 3 variations of the CAN controller/transceiver circuit and which SPI bus they were connected to, making debugging difficult. Some used different footprints, while others used different parts. This also made inventory a challenge, as each board had its own very specific set of components.
To increase board consistency and ease debugging, we propose a controller board that consists of shared core components such as the microcontroller, CAN transceiver, and possibly some debug LEDs or IOs. These controller boards would likely use a mezzanine connector to allow breakouts to carrier boards, which should be much simpler.
Requirements
| # | Title | User Story | Importance | Notes |
|---|---|---|---|---|
| 1 | Include CAN, SPI, UART, SWD | CAN, UART, SWD will have headers onboard CAN lines will be routed through the board, reducing the use of T-junctions | ||
| 2 | Debug/Heartbeat LEDs | These LEDs will provide useful debug info but the I/O can still be used for carrier board purposes | ||
| 3 | Connector and wire standardization | All connectors should lock securely and be physically distinct from each other (i.e. you shouldn't be able to plug one into another), wire color should also be standardized according to their associated signals. | ||
| 4 | Switching regulator | Switching regulators are much more efficient than LDOs (90% vs 30%) |
Questions
Below is a list of questions to be addressed as a result of this requirements document:
| Question | Outcome |
|---|---|
UART/USB? If we use USB, may need serial-to-usb converters on-board (In-car debugging) | UART only, we can reprogram our ST-Link V2 Clones to receive UART |
| Daisy chaining 12V power or not (LV power granularity) | No daisy chaining, 12V power from carrier only |
| Hermaphroditic board-to-board connectors or not | Non-hermaphroditic bergstak connectors |
Switching regulator circuit or integrated DC-DC converter (board complexity, cost) | Switching regulator circuit due to price and component height |
LQFP vs UFQFPN | LQFP for ease of rework |
How many pins do we dedicate to 3.3V, 12V, and GND on the mezzanine? | 3.3V: 6 pins GND: 8 pins These were determined based on the number of pins we have left from using all the GPIOs. Ground was chosen to be on both sides to ensure a good connection. |
| 0.5mm or 0.8mm pitch mezzanine connectors? | 0.5 mm |
Key Components
Part | Info | Digikey Link |
|---|---|---|
| STM32F072CBT6 | ARM Cortex-M0 Includes CAN controller, 37 IOs, 48-LQFP | |
TCAN332DR | CAN Transceiver Replacement for the SN65HVD232DR |
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