Introduction

In the onboarding project for the Electrical sub-team, we’ll be building a fully custom VR compute module - connected to your computer through USB, capable of delivering IMU-based 3DoF tracking, all interfacing through an Arduino. You’ll learn about circuits, and the entire process of printed circuit board (PCB) design - ideation, defining user requirements, system design, component selection, schematic capture, layout, routing, and ordering with manufacturer requirements.

Arduino Pro Micro breakout board pictured above. Can you identify the various components soldered on the device?

Typically, you can prototype an IMU (inertial measurement unit) connected to an Arduino using a breakout boards and a few wires, but that’s not what we’re doing. You’ll be learning how to build your own breakout board, but with all the components you need integrated into one single board. Forget having to connect multiple boards, and forget about the mess of wires.

• Optionally, you can decide to build a board with just an LDO (linear dropout regulator - will be explained below), and pick your own connectors. This is a little more straightforward, as you’re dealing with just the power electronics and can forget about the MCU implementation (which is time consuming).
• That would mean you could skip most of the information on gaining a system-level understanding of the VR device below.

Let’s begin!

Electronic components

When starting a design, it can generally be useful to start reading datasheets of the components you’ll be using, as well as viewing community-made designs similar to what you’re going for. However, today, we’ll explain roughly what you need to build your device.

We’ll build your understanding of the objective by first learning about the individual components, and then tying it together with a high-level overview of how each component in the system comes together to create the VR device.

USB connectors

• Your input and output interface for power and data on your board is USB. Modern chips use USB-C, but USB Micro-B is simpler and still widely used in Arduino boards. It’s up to you to select which USB receptacle you want to use.
  • All modern USB connectors do 5V, but keep in mind that USB-A was designed to deliver power, not receive it on a host device.
  • Micro-B and (especially) USB-C were designed to handle power as an input, and as such, they can do 5V at much higher current values. You will need them for your board.
  • Micro-B is generally much simpler to implement.

The two connectors that you would be able to pick from. Pictured are plugs, but you likely want a receptacle for your board.

Microcontrollers

The microcontroller (MCU) chip on the Arduino Pro Micro is the ATmega32U4, which we’ll need to incorporate into our design.

• BONUS: Try implementing a design with a different microcontroller! For example, our team has a revision of an integrated motherboard with an RP2040 and ICM IMU. Be careful when selecting an MCU - remember the system, and its requirements. Read the datasheets!

Variant of the ATmega32U4. Seems to be a QFN package, which is commonly used on PCBs.

• This will require power (switchable between 5V and 3.3V), as well as common components, such as resistors and capacitors. For our specific design, we’re going to want our ATmega32U4 running at 5V/16MHz, as this is what works best with our drivers/software.
• Microcontrollers often need a specific crystal oscillator in order to facilitate timed activities with a high-speed clock. Read the datasheet for the chip and find what’s required.