Any worthy racecar needs various sensors that will communicate with the on-board computer to improve vehicle performance. In the context of the McGill Formula Electric 2022 (MFE22) racecar, we use 16 strain gauges -- 4 per wheel.
A strain gauge is an electrical sensor that can be built with a simple printed circuit board (PCB). When our racecar has to take sharp turns, to accelerate quickly or to run over a bump, many parts experience mechanical stress that is often invisible to the naked eye. A strain gauge sensor allows to measure that stress.
In fact, when a force is applied to the strain gauge, the resistance changes. This can be used in an electrical circuit in order to transform that change into a comprehensive signal.
This article is published in collaboration with JLCPCB. With over a decade of experience in PCB manufacturing, JLCPCB provides some of the highest-quality PCBs available at the lowest-cost.
First, we need to make a schematic in Altium Designer or any other PCB design software. The schematic needs to be complemented by appropriately-sized components such as the INA818ID amplifier.
Our board is powered by a low voltage 5V input. We used a quarter-bridge or full-bridge custom configuration with very precise resistors (0.1%). The electrical output in W+ and W- then enters our INA818ID amplifier and is amplified 85 times. You can modify the amplification gain by changing the value of the R4 (600ohms) resistor. We also use a precise voltage reference of 2.5V in our amplifier by having the MCP1525T-I/TT perform that task. The output is then sent into a MicroClasp header that we can connect with wires into our vehicle controller computer.
The second step consists of physically placing the components on the PCB, ensuring the right footprints are being utilized. On a small board like this, using a polygon pour to connect the ground (GND) plane is very beneficial. Even complicated traces and polygons on such a small board will be precisely manufactured by JLCPCB, so use that to your advantage.
Once the design of the PCB is done, it is time to generate the files that will be sent to JLCPCB to manufacture it. These files are called Gerber files and they are an industry standard used to describe PCB fabrication data. Each layer of the PCB (copper layers, solder masks, overlays, etc.) corresponds to a single file.
To make them ready for ordering, combine all files into a single ZIP archive.