Ultrasonics
Several projects have been undertaken in the field of ultrasonics. Pulses of high frequency sound may be used for ranging and location and probing materials.
Ultrasonic ranger
Circuit of a miniature PIC based ultrasonic ranger
The low power ranger shown below detects the presence of an object using a single transducer. Burst generation and object detection is performed digitally in a single PIC using the internal ADC to sample the echo, after active filtering and peak detection. All parameters are adjustable in software and the device runs from a single lithium AA battery.
Initial prototype
Ultrasonic Downconverter
A passive downconverter can translate ultrasonic signals to the audio band, which has applications as diverse as air flow monitoring, leak detection and bat monitoring.
Ultrasonic downconvertor board
When the downconverter local oscillator is used as a transmit source (FM chirp with homodyne mixing) the Doppler shift from moving objects can be measured and analysed.
The unit has an exceptionally sensitive preamp and Knowles microphone with active filtering. It is capable of detecting Doppler shift in moving air currents out to a distance of 10m or so, using a small parabolic reflector.