Avian’s Blog

Here's the final form of my ultrasonic downconverter:

It features 30 - 100 kHz input frequency range and 15 kHz bandwidth. It's a fully analog design that uses heterodyning for frequency shifting (the left knob controls the frequency of a local oscillator which is then mixed with the signal from the sensor). Output port can be used with headphones or a small speaker.

It was completely designed with free software tools from the gEDA project (and OpenOffice.org for the stickers).

The piezoelectric ultrasonic sensor is detachable so different kinds can be used (for different sensitivity and directivity).

It works surprisingly well considering my problems with noise on the protoboard. The grounded metal case really makes a big difference with such a sensitive circuit.

After a couple of walks around the house I found that the most loud things in the ultrasound spectrum are compact fluorescent lamps and motion detectors in car alarms.