@zander No, I'm using a Raspberry Pi 3B+. I described my setup in my first post.

@zander The fact is, the very first time I used the setup and code it worked perfectly. I'd call that "normal." It somehow gets "contaminated" by ...

@zander It's the output pin from the sensor that goes high. I don't know C, but I'll try to rewrite the code in C. Thanks for your input!

@davee Hey, Dave! First off, thanks for the time you put into your reply. It is reassuring to know there are folks out there who want to help. ...

@zander I had tried what you are suggesting and it doesn't help. The real mystery here is why the code works initially, but after going headless a...