Kart/sensor board

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Contents

FPGA motherboard

Inputs and outputs

End of turn switch

The end of turn switch is located in the I/O board's middle row. It is the 4-pin connector closest to the 5-pin connector. The switch cable is to be connected as:

cable pin
green 5 V power supply
yellow input

The input has a pull-down resistor. Closing the switch brings a logic '1'.

Hall sensors

The sensor connectors are located in the I/O board's middle row. The sensor cable is to be connected as:

cable pin
red 3.3 V or 5 V power supply
brown sensor signal
black ground

Ultrasound ranger

The sensor connectors are located in the I/O board's middle row. It is the single 5-pin connector. The sensor cable is to be connected as:

cable pin
red 5 V power supply
yellow measurement start (trig)
green echo signal (distance)
black ground

Proximity sensors

The sensor connectors are located in the I/O board's side row.

The sensor cable is to be connected as:

cable pin
orange 3.3 V power supply
yellow SDA
green SCL
blue ground

LED outputs

The board has 4 LED outputs which can also be used for other purposes, such as buzzers.

The outputs have a common power supply, 2 resistor mount holes and a 2-pin LED connector located on the I/O board's bottom row.

The power supply is connected directly to the 12 V battery packs. The resistor is connected between the power supply and the LED. The LED is connected between the resistor and the ground.

FPGA design

One or two Hall sensors are used to track the driven distance. An ultrasound ranger can detect if there is an obstacle at the front of the kart.

To begin with, the design environment has to be downloaded. It comprises the dcMotorController block which contains the provided I2C bus interface and an empty dcMotorPwm block which is to be designed.

Hall sensor

The hall sensor.

The block receives a speed signed number and has to drive the DC motor with a pwm and a forwards signal. These signals are sent to the daughterboard in order to drive an H-bridge. The daughterboard logic drives the bridge's power transistors from the two signals. The mean amplitude of the DC motor's voltage is controlled by Pulse Width Modulation (PWM).

The forwards signal is derived from the sign of the speed control. The pwm signal is derived from the absolute value of speed.

The PWM signal is implemented with the help of a free-running counter and a comparator. However:

  • the power transistors cannot switch at too high frequencies
  • there is a need for a dead time where all power transistors are open between the PWM transitions

Because of this, the PWM period is limited to a minimal value. This is achieved with the help of an en signal generated by a counter dividing the clock frequency. The counter only increments when this en signal is '1'.


View-pim-tasks.png

Draw the schematics of the dcMotorPwm block.

The minimal value of the PWM signal is studied in another part of the kart project. The period of the en pulse train is set in the DC motor PWM period register.

Ultrasound ranger

The ultrasound ranger.

In order to cope with this, a setup signal, normalDirection, is provided to the block. normalDirection being '1' means that a positive voltage applied to the DC motor lets the kart drive forwards.


View-pim-tasks.png

Update the schematics of the dcMotorPwm block in order to cope for the different mechanical design possibilities.

The setup bit is configured in the hardware control register.

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