Review: Ultrasonic Rodent Repellers – Operation and DIY Construction

The other device is a lot more expensive and is designed and manufactured in Sweden. According to the manufacturer it produces a variable ultrasonic frequency, so that mice do not become accustomed to a particular frequency. On the back of the circuit board in the enclosure there is a reasonably extensive electronic circuit with, among other things, a 556 dual timer IC.

When measuring the acoustic signal it does turn out that the manufacturer's claim is indeed correct, the little speaker generates a swept frequency between about 20 and 60 kHz, with a greatly varying amplitude. That variable amplitude can probably be attributed to the efficiency of the piezo element. This happens to peak at a frequency of about 40 kHz, but is much lower elsewhere, particularly at lower frequencies.

The oscilloscope image shows a period of nearly 1.5 seconds and the frequency changes continuously during this time. All up, this is a very well thought-out design and the construction is a lot better compared to the Chinese version, it even has a glass fuse.

This device also generates electromagnetic pulses on the mains wiring via a small transformer. Something that mice and rats are also not supposed to be happy with. I have, however, not been able to test the functionality of that.