Inside a sound detecting dusk switch with interesting circuitry

This device detects dusk and only turns a light or other load on for a fixed time if it hears a noise. That could be useful as a security device, as an alternative to a PIR sensor.

The circuitry is notable for using a common technique for switching medium loads with very low control current. But that does limit the power it can switch.

This circuit has lots of interesting quirks. From the load switching to the use of the chip's internal pull up resistor as part of the dusk sensing voltage divider.

These have been around a long time, so they're probably available from all the usual online marketplaces. Here's an affiliate link to where I bought this one from:-
https://s.click.aliexpress.com/e/_c4EzVlgX
If you add it to your basket it may appear as a bundle deal. It should cost £2 or less.




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