[time-nuts] Simple AC mains zero-cross detector

Dave M dgminala at mediacombb.net
Tue Dec 16 20:58:22 EST 2014

Charles Steinmetz wrote:
> Every so often, the subject of logging the zero-crossings of the AC
> mains comes up.  There are any number of ways to couple the AC mains
> to logic circuitry (coupling with very high value resistors,
> capacitor coupling, and optical isolation have been mentioned).  A
> simple AC mains ZCD that is transformer isolated and gives excellent
> results, is posted at ko4bb.com:
> <http://www.ko4bb.com/manuals/download.php?file=05_GPS_Timing/Simple_AC_Mains_Zero_Crossing_Detector.pdf>
> The ZCD uses a small, dual-primary power transformer, two
> transistors, and a few diodes, resistors, and capacitors.  It
> produces a ~100uS logic-level pulse at every positive zero-cross, the
> leading edge of which is predictably and stably related to the AC
> mains zero-cross.
> Best regards,
> Charles

I'm not trying to downplay the circuit in the link above, but I want to 
offer another possible solution to Zero-Crossing needs.

Here's an Idea For Design from EDN magazine that I've used a couple times in 
non-time-nut circuits, and I must say that it works beautifully.  I have no 
measurements that would satisfy a time-nut's curiosity, so if someone wants 
to Spice it or otherwise tear it apart, please do..
My use for the circuit was in a spot welder control; the output was used to 
sync and cycle a counter-driven trigger for an alternistor, all of which 
controlled the number of power line cycles that the welder transformer 
received for the weld. It worked well for me until I sold the whole 
contraption.  Don't know whatever happened to it after the guy moved away 
from the area; never heard from him again.  I hope it's still working.


Dave M 

More information about the time-nuts mailing list