In SX Microcontrollers, SX/B Compiler and SX-Key Tool, william wrote:

Beau,

AC Freq here is 50Hz, lower than 120Hz.
But I think the noise is not coming from the 50Hz power but rather from spikes created by the starter and the fluorescent tube when trying to switch on (strike) or when switching off.

Or could it be spikes that were created when the mechanical relay switches on or off the power to the fluorescent lamp.
Unfortunately, mechanical relay switching cannot implement zero crossing detection.

What frequency should spikes usually be?

Atttached is the schematic.  It may look odd, but it works with the Parallax PIR sensor.

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