Ultrasonic Transducers

1
Ultrasonic Transducers

• Cueillir Special Sensor
• Kurt Rooks
• IMDL/REU Summer 2007

2
Ultrasonic Transducer

• Can function as either a transmitter or receiver.
• 25 kHz sound wave (the human ear can hear up to
  20kHz).
• Bandpass filtering limits variations to 24 kHz
  to 26 kHz.

3
Ultrasonic Transducer

• Effective range of about 3 meters.
• Effective cone of about 45 degrees.
• No on-board processing included.

4
Generate, Send, Receive
5
Generate 555 Timer
6
Transmit

• Home Base
• 25 kHz
• 4 Transducers arranged in a circle to create an
  Omni-directional emitter
• 8 Oscillations followed by 10ms of silence

• Lost Keys
• 25 kHz
• 4 Transducers arranged in a circle to create an
  Omni-directional emitter
• 16 Oscillations followed by 10ms of silence

7
Receive and Process
8
Process
9
Process

• The previous processing recreated the original
  square wave from the transmitter.
• A CPLD will be used to distinguish which
  transmitter is being received.
• The CPLD will have 5 digital outputs to the
  Atmega128, corresponding to the transducers and a
  source identifier.

10
Process

• The 4 digital input lines to the Atmega128 will
  be connected as external interrupts.
• By time-stamping each interrupt, time of
  arrival (TOA) calculations will determined the
  relative coordinates to the source.
• These coordinates will be turned into motor
  instructions to navigate to the desired source.