[time-nuts] Clocking a PIC16F628A from a Rubidium Standard

David VanHorn D.VanHorn at elec-solutions.com
Mon Nov 28 13:56:41 EST 2011

> Let's not be obtuse on purpose, David.

No amount of dancing is going to turn this into a design that is safe by any reasonable definition of the word.
"Safe" in terms of "it hasn't killed anyone yet" is probably true.
"Safe" in terms of "you can trust this device not to cause a fire", no.

To quote from the page:
There are no safety worries about voltage, current or power, about frequency, shock or shorting. Worst-case current is only 60 µA so you can use thin digital wire to connect the plug to the microcontroller. One wire goes to Vss (signal ground) and the other to the microcontroller digital or analog input pin. If it doesn't work the first time, swap plug polarity. Or use capacitive coupling on both wires.

Of course, the whole idea of this AC plug is unnerving at first but when you think about it, it makes sense. Better yet, just make one and test it for yourself. You should observe it tickles far less than a 9V battery (which I measured to be about 200 µA on a wet tongue). 

Does that last line actually suggest checking this contraption BY TOUCHING IT TO YOUR TONGUE???

"No safety worries about voltage...or shorting" ??  Resistors can and do fail shorted. They can also be damaged by line voltage transients and end up at some lower value.

What version of "safe" applies here?

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