💾 Archived View for tilde.pink › ~ssb22 › cat.gmi captured on 2023-12-28 at 15:46:23. Gemini links have been rewritten to link to archived content

View Raw

More Information

➡️ Next capture (2024-02-05)

-=-=-=-=-=-=-

Cat scarers becoming audible

When we moved into a house whose garden was frequently visited by defecating cats, the sellers left us a couple of ultrasonic cat repellers (they looked like PestBye’s product) which seemed to be effective for a while, but then a younger guest said she could hear the sound, and a few months later *we* could hear the sound as well. As we weren’t expecting our hearing sensitivity to be ageing in reverse, we looked for a failure mode that brings the cat-scarer’s sound back down into human hearing range as the device gets older.

It turns out there *is* such a failure mode:

After cutting into one of our cat scarers with a small saw (which generated rather a lot of plastic dust and is not to be recommended), we were able to observe its circuit board. Apparently, it had been made 7 years earlier in 2016, had no country of origin declared, and somebody couldn’t spell “sensor” but never mind. The circuit had connectors for solar input (but that wasn’t fitted on this device), and legible components included a BISS0001 PIR controller chip, an HT7125 low-dropout voltage regulator, an NE556 timer chip (for keeping the alarm on after motion is detected), and D882 and 2N2222 amplifying transistors. As I’d suspected, the oscillator was not on an IC but was made of discrete components, and the biggest capacitors were 2 x 22 micro-farad and 3 x 220 micro-farad cylindrical electrolytic, with possibly some smaller ceramic chip capacitors as well (it was hard to see exactly). There were also signs of water ingress, possibly due to the rubber seal around the battery holder not being properly refitted after changing the batteries.

I suspect mains or solar cat scarers might be less likely to be damaged in this way over time than battery-powered ones (because the event of changing the batteries is a time when things can go wrong) but any circuit may eventually be vulnerable, and having the frequency reduced to a level that at least some humans can hear seems to be a common failure mode causing many complaints about neighbours’ cat scarers, so it’s probably important to ensure they’re still in good condition and this frequency-reduction failure hasn’t happened.

Legal

All material © Silas S. Brown unless otherwise stated.