Project overview: 

This backplane board was designed for use in the current robot from the Underwater Robotics Team at The Ohio State University, Project Titan. The backplane board is used to connect our four other custom PCBs together to ensure that signals and power are routed to the proper destination without the need for an exhaustive wiring campaign.  

Working Principals: 

Additional custom boards are slotted into the edge connectors that are then routed together to electrically connect the boards creating an effective electrical system. Our boards feature connections such as: I^2C, many PWM pins to control thruster speed, power traces connect 5V and 3.3V to our custom boards and many more. The Backplane board is the central hub for all communication that occurs between our boards and provides a nice central connection scheme that better organizes our robot’s electrical design. 

Schematic design: 

Schematic design is broken into three major categories: mounted headers, off-board connectors, and test pins. Autodesk Eagle is a freely available program that allows schematic creation as well as PCB layout design. On the left-hand portion of the schematic, we’ve organized our four headers in a grid. If you are making your own header Eagle packages, make sure name each pin for its appropriate function on your additional boards and affix a label marker to keep your schematic readable. 

Next, you will want to add any off-board cable connectors in the same fashion as your main headers. For our project, we’ve opted to include Molex Mini Fit Jr. connections for a kill switch, I^2C sensor, depth sensor, and acoustics setup. For connections that will be removed and reattached regularly, it is good practice to include a simple LED circuit that indicators a connection is successfully made. 

Available test pins can make debugging your backplane much easier. Including female pins for a digital voltmeter on lines such as ground, basic voltages (3.3V, 5V), or any important connections to your project allow you to quickly test if a trace or component has failed somewhere.                                     

Board layout: 

Using a two plane (top and bottom) PCB layout can help keep routing clean with the use of a ground plane. Create a blank PCB with the dimensions of your preferred project layout, making sure to include holes for any mounting points you would like to use. Your bottom plane can consist of a polygon plane labeled ‘GND’ that spans the full length of your board, sinking any ground connections on your components to a large thermal area. Next, position your connectors and headers relative to where you would like components to face in your project. The Underwater Robotics Team uses a cable bundle positioned at the end of the board to feed off-board connections with our function boards inserted vertically into the four vertical headers. 

Take care to connect each valid electrical connection from your schematic with the appropriately sized trace widths, relating the expected current to the necessary thermal width. Printed text labels can help to keep your connectors clear and easily followed, especially when choosing the right test pin when debugging. 

 A big “thank you” to JLCPCB for helping us manufacture our circuits. We have worked with JLCPCB in the past and they have always delivered quality on time. It is hard to beat their competitive prices and we look forward to working with JLCPCB again in the future. If you are interested in getting your hands on a custom circuit, check out JLCPCB here: https://jlcpcb.com/.