[time-nuts] Line Frequency

Tom Van Baak tvb at LeapSecond.com
Mon Feb 10 12:57:51 EST 2014


> You should really have isolation from the mains. The transformer scheme
> is fine. I don't like the high value resistor approach.  

I know what you mean. I too used to think isolation and safety meant using a transformer, like a low voltage AC wall-wart.

Then out of curiosity I opened some of them to see what was inside. Sloppy design. Poor soldering. Child labor. Solder drips. No waterproofing. Fingerprints. Vinyl tape. Compared to that, a DIY, carefully constructed, direct connection of two AC lines to PIC input pins via a pair of 1 Meg flameproof resistors has merits.

Perhaps what we need is transparent wall-warts, like hospital-grade power cords.

Alternatively, has anyone considered grabbing 50/60 Hz from the air? Just about any dangling unshielded wire will act as a pickup. Maybe not as robust a signal, but this is not so much a problem for solutions already using a hardware or software PLL. And it certainly wins the safety prize. Call it the iClock Air...

/tvb



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