Top Dutch Solar Racing

Top Dutch Solar Racing is a student team from the North of the Netherlands whose goal is to build a solar car to compete in international solar races. Like most other vehicles, our solar car has an electrical system which of course consists of multiple PCBs to ensure a smooth cooperation between all parts of the car. Luckily, Eurocircuits provides us with their excellent manufacturing for all our PCBs. In this blogpost, I will introduce the PCBs that we developed for the production of the car and then zoom in to the PCB used in the steering wheel of the car.

BMS

The Battery Management System (BMS) slaves and master ensure that the car battery can safely charge and discharge. Additionally, it keeps track of many critical parameters such as the temperature and voltage of each of the cells.

Motor Controller

The Motor Controller consists of two PCBs and has several functions within the car, for example the acceleration and braking of the motor, regulating the speed and avoiding overloads. Besides that, the Motor Controller represents a bridge between the AC motor and the DC battery.

MPPT

The Motor Controller consists of two PCBs and has several functions within the car, for example the acceleration and braking of the motor, regulating the speed and avoiding overloads. Besides that, the Motor Controller represents a bridge between the AC motor and the DC battery.

MPPT

MPPT Switch

All MPPT’s are connected to the MPPT Switch, which can be seen as a bridge between the MPPT’s and the car battery. The MPPT Switch is responsible for inhibiting the charging of the battery when the car is turned off.

Lighting

The Lighting PCBs speak for themselves – they are needed to control and mount the lights of the solar car.

Steering Wheel

The steering wheel PCB is part of the Human Machine Interface (HMI) and it enables the pilot to control and communicate with the electrical system. The steering wheel includes a display, several buttons and two flippers to control the rest of the electrical system, including acceleration and regenerative deceleration of the electric motor (with the flippers).

Steering Wheel PCB

Rear View Display

Finally, there is one more PCB that is also currently in development which is mainly responsible for driving a display which shows an image of the rear view camera of the car. Also, the horn, the braking sensor and some fans are connected to this PCB. This PCB, together with the steering wheel, form the HMI.

Rear View Display PCB

Steering Wheel

During the race, we want our car to be as user friendly as possible for our drivers. To ensure this in such a limited space, almost the whole HMI has been incorporated into the steering wheel. As said before, the steering wheel consists of multiple buttons, two flippers, and an information display.

The PCB is controlled by an STM32 microcontroller and supplied with 24V CAN-bus voltage. There is only one connector on the PCB for both the CAN-bus voltage and data. Having only one connector is important because having multiple or thick wires coming from the steering wheel would add friction while steering. Using switching regulators, the 24V supply is lowered to both 5V and 3V3, which are necessary for the MCU and the display respectively.

Steering Wheel PCB with Legend

Display

A very power-efficient 4.4 inch black and white TFT LCD is incorporated into the steering wheel. It is used to display all necessary information, such as speed, to the driver of the car. The display has a tiny power consumption of 650 uW and uses serial communication and custom drivers written by our software engineers. In the picture below, you can see a preliminary version of the software. This layout of the display is just a mock-up our software engineers made for testing. Now that they are capable of displaying this, however, they can display anything we want.

Front of PCB including display, buttons and indicator lights Flippers

Two small separate PCBs are connected to the main PCB of the steering wheel by using headers. A magnetic rotation hall sensor is mounted on each of these tiny PCBs. These sensors are in line with an axle in which a magnet is mounted. This axle is attached to a flipper that the driver can move. When the driver moves either the acceleration or regenerative deceleration flipper, the axle (and therefore also the magnet inside that axle) are rotated. This magnetic field rotation is measured by the hall sensor and converted to an analog signal which goes to the MCU. After that, these values are finally transmitted via CAN-bus to the motor controller, which in turn drives the motor accordingly.

Flipper PCB with Hall Sensor

Other small features

Apart from the features mentioned above, the steering wheel has some other small features which are worth mentioning. The steering wheel measures both the temperature and the relative humidity inside the cockpit of the solar car with an I2C sensor IC. Next to that, there are a few LEDs on the top of the PCB which show the driver when the indicators are turned on, the LEDs are also driven using an I2C LED driver IC. Finally, there is a buzzer mounted to the PCB which makes a noise whenever a button is pressed, this feature makes sure that the driver knows for certain when a button press is registered.