Over the last year or so I’ve been working on a lightning sensor system for my weather station. I originally found a circuit published by Charles Wenzel that I thought looked interesting, and I decided to give it a try. The circuit worked quite well. So well, in fact, that it picked up lights turning on and off around the house. It also goes wild when the stove-top in the kitchen is used. I guess the stove has a noisy PWM circuit or something. I made a PCB for the circuit, and integrated it into my weather station and have let it run for a few months now.
As the summer draws near a flaw in this design has presented itself. The flaw is severe temperature instability. Hotter temperatures increase the sensitivity of the system, and on hot days the thermal noise of the circuit causes a significant amounts of false triggers. This will be addressed in an upcoming design change in an attempt to reduce the number of false triggers.
The event on May 4th was an actual lightning storm and strikes were observed by persons in the area. Note the large drop in barometric pressure preceding the rise in lightning strike counts.