An LDR based motion sensor

[ledtester]

 found this interesting so I thought I'd tell other people about it...

I happened across this video which goes through the design of a motion sensor based on an LDR:

Motion Detector without PIR module! Analog circuit Explained - Electronic Wizard
https://youtu.be/9axYfWQQdno

It does a good job of incrementally developing the circuit and troubleshooting the problems encountered along the way. Attached is the final schematic. Overall it looks like a fun circuit to breadboard up and play with -- in the video the author says he could "play with it all day".

In researching the circuit I found it is also known as a "data slicer" which has applications in handling Manchester encoded signals. Here's a blog post in which one person compares the data slicer to other op-amp circuits in finding a "pulse" in a signal:

https://electronut.in/designing-an-op-amp-circuit-to-detect-ldr-pulses/

[StillTrying]

Reminds me of an idea I had 5 years ago to make a 'yard intruder detector', perhaps.

Using 2 small LDRs very close together behind a 2 or 3 cm diameter lens the idea was that it could be inside looking out of a window. Two LDRs in series so that it automatically adjusts from daylight to darkness, in theory.

After spending an hour matching 2 LDRs in room light, I gave up on the idea.

[RJSV]

   Drug store toys Dept. sold me my Halloween themed toy that used an LDR motion detect, (and without an IR light nearby).   The toy was a fake 'instant' Polaroid style 'camera' that blinked a strobe 'flash', then opened a slide drawer, supposedly with Polaroid single photo.
Assuming most was done in software, flexible code could use the analog values to detect various changes in light level, for a robust motion detection function.

   If I had written it, the code would basically figure out the current average light levels, and monitor for faster changes, while keeping track, as general light levels slowly shift.