Subject
Design and validate the architecture of a rear parking aid, as found on most cars, covering two parts:
- Radar: a single range sensor mounted behind the car.
- Interface: inside the car, separate from the radar — a beep tone and an LCD screen displaying the remaining distance.
Work Done
System modeling
Communication system
The top layer, "Liaison," transmits a message from the producer and waits to receive and acknowledge it before handing it to the consumer. If a NACK is returned, or the timeout period is exceeded, "EmissionLiaison" re-sends the message (up to 3 times).
The layer beneath, "Framing/Deframing," wraps the message with a Start-of-Text (STX) and End-of-Text (ETX) character, plus a checksum before ETX — three characters added to the message, letting "Deframing" find the message bounds and verify its content via the checksum. Any error returns a NACK.
The bottom layer, "Character Transmission," decomposes and reconstructs each character as a binary sequence with a sign bit for validity checking, immediately above the transmission channel itself, where noise can enter the stream.
MATLAB modeling
The ultrasound transmitter/receiver is modeled with a second-order transfer function:
We apply a bilinear transform (Tustin's method):
Which yields:
Using MATLAB's filter function, with delay added in proportion to distance, a square-wave input produces:
For digital signal processing, this transfer function converts to a recurrence relation:
With the following coefficients:
Accounting for delay and attenuation proportional to distance, simulation gives:
- In blue, the burst (square signal)
- In red, the echo received by the system
Platform & code
- Range sensor: HC-SR04
- Processing platform: STM32 NUCLEO-L152RE
- LCD interface platform: MCB STM32F400