[Milsurplus] Crystal tester

[Al Klase]

Gang,

Crystal testers have been of interest to me for a long time.  There are 
a lot of published circuits out there, and there have been some actual 
products over the years.  Most of these work just fine for crystal in 
the MHz range, but don't work well with things like 100KHz calibrator 
xtals or military FT-241's that are the the 300-500KHz range.

Most modern devices implement crystal oscillators by biasing a CMOS 
logic gate/inverter into analog operation by connection a 1-2 meg 
resistor from input to out put, and connecting the crystal like so:


This Texas Instruments app note dopes out the whole matter: 
http://www.ti.com/lit/an/szza043/szza043.pdf

Basically, all one has to do is change the value of Rs to accommodate 
different frequencies.  E.g. 50K ohms for 100 KHz rocks.  I started in 
on this a while back and had encouraging results with a 100K pot for 
Rs.  (can't find my breadboard. :-()  I intend to add some sort of 
analog meter to the output of the oscillator gate to indicate activity, 
and buffer the output with the other devices in the IC to and output 
connector and possibly a $10 counter module from E-bay.

Too many projects!
Al

-- 
Al Klase – N3FRQ
Jersey City, NJ
http://www.skywaves.ar88.net/

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