Introduction: Datalogger System for Formula Student
Formula Student the world most established educational engineering competition which uses motorsport to inspire students.
Backed by industry and high-profile engineers such as Patron, Ross Brawn OBE, the competition aims to develop enterprising and innovative young engineers and encourage more young people to take up a career in engineering. The format provides an ideal opportunity for students to demonstrate their engineering knowledge and test and improve their capabilities to deliver a complex and integrated product in the demanding environment of a motorsport competition.
The main function of the datalogger module is to read two CAN communication BUS and record the information present on the BUS on an SD card at a rate of 200Hz, to later analyze the information regarding the vehicle's operation. In the module developed as it is to be integrated in a vehicle to compete in the formula student event, it has incorporated other features such as:
• 2 digital and 4 analog inputs with respective signal conditioning;
• 4 status smd leds;
• A 5V Series and 3.3V communication bus;
• Lap trigger;
• RTC to know exactly when the data is being recorded,
• A circuit capable of detecting a power failure in the module's power supply and ordering the closing of the SD card beforehand for not to lose the data acquired.
The whole system was designed with the aim of being as compact as possible.
• CAN MCP2562 transceiver;
• Voltage regulator switched from 12V to 5V R-78E5.0-1.0 Recom;
• Ampop Comparator MCP6542.
Step 1: Design
The module is powered by the vehicle's 12V battery in which the current will pass through a diode for protection and the 12V to 5V switched regulator has been selected since it is more efficient and the heating will be almost zero. For the protection circuit against power failure, the voltage of the 12V vehicle battery is compared with the internal 5V of the plate when the vehicle's supply voltage drops below a certain level, the microcontroller will receive the order to close the SD card . For the CAN bus communication, the tranceicer MCP2562 was selected because it allows the selection of the logic communication voltage with the microcontroller also the board has incorporated a CAN bus end resistor in which it can be activated by a jumper.
4 smd leds were added in order to debug the module in which one led is dedicated to the 5V power, one to the CAN 0 bus, another to the second CAN bus and lastly a led to know when the uC is writing on the SD card.
Since this project presents you need a microcontroller with some processing capacity to achieve the objective of reading two CAN buses, reading signals on I-O pins and recording the information obtained in a TXT file present on an SD card at a rate of 200Hz. For this, the Teensy 3.6 microcontroller was selected, which satisfies all needs.
Step 2: Prototyping
Before proceeding with the manufacture of the PCB, the developed schematic was tested on breadboard in order to validate it to make sure that the module would work as intended. For this, the schematic was mounted on a bench where an adjustable power source was used to simulate the car battery and power the module and a CAN module to send information and simulate the vehicle's communication bus.
Step 3: Design PCB
Taking into account the application of this module, since it is to be in the formula type vehicle, there was a need to develop the PCB with the smallest dimensions possible. For this purpose, very small sizes were defined for the thickness of the PCB tracks (0.18mm) and tracks (0.35-0.7mm) in order to save space and the components were positioned in order to minimize the free space on the PCB. As a final result, the PCB shown in the figure was obtained with the following dimensions 65x64 mm.
Step 4: Ordering the PCB
We choose the JLCPCB because offers fast, high-quality service at reasonable prices.
1. To order visit https://jlcpcb.com & sign in/sign up.
2. Click quote now button 3. Click on the “add your gerber file” button and upload your gerber files Now you can set your parameters and customizations, such as quantity and PCB colour;
4. Click “SAVE TO CART”;
5. Go ahead and type your shipping address, choose the shipping method;
6. Process to submit your order and payment;
7. The PCBs our team ordered came within the week.
Step 5: Assembly
As the last step of this process, after receiving the PCBs sent by the manufacturers and gathering all the necessary components, the final assembly of the modules for implementation in the car was carried out, as shown in the figure.
Then is welding carefully every component to the PCB and test to evaluate if everything works fine :)