Kart/serial link

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Serial link protocol

This section defines the serial link protocol used to communicate between the Kart and the SmartPhone. All data is spontaneously sent.

Serial port

Communication is done with:

  • 115200 baud
  • 8 bits
  • no parity
  • no handshake

Message Format

SoF (1 byte) Address (1 byte) Data (2 bytes) EoF (1 byte)
0x55 UINT8 UINT16/INT16 0xAA


SmartPhone to Kart

Address Datatype Description
0 UINT16 DC motor PWM period
1 INT5 DC motor speed: -15 to 15 (Negative numbers = backwards)
2 UINT16 Stepper motor period (speed proportional to 1/period)
3 UINT16 Desired steering angle (angle in motor steps, 0 = end switch)
4 UINT5 End switch address
5 UINT5 Hardware control
15 UINT16 Serial link update interval [ms]

Hardware control register

Bit Meaning Description
0 Kart goes as DC motor When '0', the kart goes backwards when the motor turns forwards
1 Kart turns right (clockwise) When '1', kart turns to the right as stepper motor phases go from 1 to 4
2 End sensor is on left side If '1', the angles are measured clockwise
3 Stepper end Emulates an end switch contact for the direction motor
4 Restart Puts following slaves back in startup mode: stepper motor
The DC motor is stopped as long as the signal is active
5 Bluetooth connected Indicates that the Bluetooth connection is established

The end sensor always defines position 0. Angles are always positive.

If bits 1 and 2 are different, the stepper motor phase sequence has to be inverted.

If the Bluetooth connection is lost, the DC motor has to be stopped.

Kart to SmartPhone

Address Datatype Description
0 UINT16 Hall speed count 1
1 UINT16 Hall speed count 2
2 UINT2 Steering status: bit 0 stepper end, bit 1 position reached
3 UINT16 Actual Steering Angle
4 UINT1 Stepper End from I/O board, bit 0
5 UINT16 ADC Value of the Battery Voltage Level
6 UINT16 Distance
8 UINT16 Proximity 4
9 UINT16 Proximity 3
10 UINT16 Proximity 2
11 UINT16 Proximity 1
12 UINT16 Ambient Light 4
13 UINT16 Ambient Light 3
14 UINT16 Ambient Light 2
15 UINT16 Ambient Light 1

Kart I2C bus

The data on the kart's I2C bus reflects the one on the RS232 link. On the I2C, both data and addresses are 8-bit.

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