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

ed breya eb at telight.com
Sat Nov 26 13:57:55 EST 2011

How did such a trivial circuit function for a one-unit application 
trigger such a large philosophical discourse? I guess I'll put my 
one-cent's worth in too. If you were designing to make a 
mission-critical item, or millions of units, then every part and 
every penny would count, so the finesse requirement would be high, 
and the details critical. But this is not the case here.

All you need is an NPN open collector - a simple Q circuit - or the 
output of an OC TTL or OD CMOS gate to eliminate the powered v. 
unpowered states issue. Let the gate or Q circuit be driven from the 
Rb source +5 V and 10 MHz signal, and let the collector/drain output 
be pulled up to the PIC supply. If there is concern that for some 
reason the gate open-device output may not work right when the gate 
is unpowered, then just build it and see, or just use a transistor circuit.


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