Centerboard PCB Project

For this week’s project, you’ll be tasked with recreating the center board schematic and PCB in EasyEDA. The prerequisite to this training is to be added to the team workspace; if you haven’t done this yet please reach out to one of the leads with your email.

The center board is an older board that was designed to break out power and signal in both robot bottom and top. On the bottom, it takes in power from the PMM’s chassis port and signal (CAN line) from the Nucleo via slipring. On the top, it takes in power from the PMM’s ammo port via slipring and takes signal from the Nucleo.

Step 1: Joining the team workspace

All of TR’s boards are available in a shared workspace. Here, you will be able to create your own projects as well as view and edit other people’s projects. Some general guidelines for keeping it clean:

• Let’s assume your board is named Project Name.

  • Name your schematic Project_Name_Schematic_V# where # represents the version number for your schematic.

  • Name your PCB Project_Name_PCB_V# where # represents the version number for your PCB.

  • Example:

    

• If you are finished with a PCB, highlight everything and select Lock. This prevents other people from accidentally moving or breaking stuff.

  

This week, you will be tasked with re-creating the center board with improved features. You are given the schematic and a reference PCB image.

1. Find the project folder titled TR Center Board Project - Training in the shared workspace (you might need to click on the “All Projects” tab on the top left).
2. Then, clone the project into your own workspace by right clicking the folder, selecting clone, and changing the owner to your personal account.

Step 2: Understanding the Design

Before you begin, take some time to explore the schematic and try to understand as much as you can. It might be helpful to review the wiring diagram too.

The general structure of the center board is as follows:

• Distributes power to motor controllers
  • Bottom right of the board sits a male XT30 connector designed to take 24V in
  • In series with a glass fuse to prevent current surges
  • Daisy-chained to 8 VOUT female XT30 ports, which C610s/C620s use for power
  • Has an indicator LED for when power is connected
• Distributes signal to motor controllers
  • Has a star(ish) CAN topology
  • Uses surface-mount 2-pin GH connectors

Step 3: Improving the Design

Center board PCB:

The center board has area for improvement. Your new design should solve the following issues with the center board:

1. Poor CAN routing:
   1. CAN not routed properly as a differential pair: Read this article to understand how differential pairs should be routed. The current design has via-in-pad routing, which changes the length of the CAN and leads to corrupted reads (remember that CAN is interpreted as the voltage difference of two signals).
   2. No termination resistor: two 120 $\Omega$ termination resistors should be placed in parallel at the physical limits of the center board’s CAN bus. You should route the CAN bus as a long daisy-chain with one end having the termination resistor. To make debugging easier, include a way to switch the termination resistor on/off. This can be done via physical switch or a 2-pin header/jumper configuration. Make sure to use a surface mount resistor (often called chip resistor).
2. Better LED design:
   1. Use KVL and Ohm’s law to calculate the current through the LED loop. Find another resistor such that the current reaches around 5mA. Make sure to use a surface mount resistor.
3. High EMI: while CAN is typically resistant to EMI, routing noisy power around it is not a good design choice. Your design should partition power/signal in a better way.