AVR-Chat

On Thu, Nov 20, 2003 at 11:42:55PM -0500, David VanHorn wrote:
> At 03:47 AM 11/21/2003 +0000, nangkon wrote:
> 
> >Thanks for the info!
> >
> >Is there an instrument (maybe Oscilloscope) to measure 
> >if the cap/crystal combination is ok? And what should 
> >I measure (frequency)?
> 
> Probing a crystal will pull it off frequency, unless you use a special high capacitance, high impedance probe. 
> 
> What I use, is a shortwave recever, with BFO. 
> This works on the radiated energy from the circuit, and does not affect the circuit at all.  If you already have a Sw receiver, then this is a very good technique, especially when you can calibrate to WWV at 10.0.. or 5.0.. MHz
> 
> I have been able to probe the crystal can, and get a recoverable signal on the scope, but it's not a very large signal, and you could be misled.

My favorite technique is to use one of the dual MMIC (MAR-6) preamp boards
to give about 40 dB gain. Then make a probe by removing about a 1/2" of the
outer insulation and braid from a piece of RG-58. When connected to a decent
frequency counter and put in the general vicinity of the oscillator, you 
should be able to measure the frequency easily.

Mike