Steering Wheel Errata

[ethanmpeterson]

Below is a list of errors I made on the steering design that we should fix in a future iteration.

• CAN bus switchable termination. Both throws of the switch are connected to CAN_P meaning it effectively does nothing. This was a net naming error and one of the labels should be changed to CAN_N.
• Power sequencing.
  • The regulators currently feed directly into one another without any kind of protection. We should add some kind of PMIC so that we don't have backpowering. Ie. when I plug in 3.3 V only, the 5V and 12 V LEDs should not turn on. This is confusing behaviour and makes you think it's working when it is not.
  • Also, both the CAN transceivers and Neopixels depend on a 5V power supply. I think it would make sense to send a PGOOD signal to the MCU so we know that are actually properly powered. This has caused a lot of grief in the past since you can run the MCU with just 3.3 V but the CAN ends up being broken. Alternatively, we could have some kind of power AND gate that only feeds power to the MCU if the 5V is also available.
• The button silkscreen is mislabeled, the text shown on the physical pcb does not match the schematic net names.
• New feature to consider: Directly integrating the debugger schematic into the steering wheel so we can do everything on one PCB.
• Break out extra IO on the MCU to a pin header so we have it for general use. Sometimes it is handy for debugging purposes. Also can save our bacon if we end up assigning the wrong pinout somewhere in our primary connectors.
• Toss the Queen's racing logo on the board!
• Make the 12 -> 5V voltage regulator a switching buck converter. We used linear in the first iteration due to lack of time / fears of it not working. It works as is but it is very wasteful on the power front and produces unneeded heat. Considering we are going through a current limited quick release connector in the steering assembly, I think it is worth doing this. Also what you are going to see far more often in industry. (Tip: many switching regulators have a PGOOD signal we could use for detecting the presence of 5V as well)