I’m working on a circuit based on a 34685-MP chip bought at Marlin P Jones. The chip is supposed to be sensitive up to 7m away, but I’m not getting very reliable detection. My first thought was that, being next to a bunch of high-frequency stuff (a Teensy 3.2 with the audio shield), maybe it was interference.

I tried taking its output to the base of a transitor and lighting a LED to see if that was better. I got similar results.

I’m not sure what’s going on yet. If I do figure it out, I’ll post here.

Update: the Interwebs deliver! Following the recommendation I found in the comments on this article, I put the 34685-MP on a cable, and moved it away from the breadboard. Voilà! It now works as I had hoped!