Ian,

 There are several ways of checking crystals for activity.  One
 of the oldest, and best IMHO, is to build a small low power
 oscillator that will accept the crystal leads, and start
 oscillating.  In this oscillator is a rectifier and sensitive
 microamp meter.  The more activity the crystal has, the higher
 the reading on the meter.  I revised the above circuit with a
 PIC so that the PIC's ADC would read the level of activity and
 display it on an LCD.  I also have a means of connecting a
 frequency counter to determine frequency.  Your DMM would work
 as the frequency counter providing it can count as fast as the
 crystal is oscillating.

 Regarding the 4 lead crystals.  Are these actually crystals or
 are they canned oscillators?  Do they look like a DIP package
 with 1 pin in each corner?  And all corners are rounded except
 one which indicates pin 1?  If this in fact is what you have,
 then pin 1 can be either N/C or a TRISTATE pin, Pin 7 is GND,
 Pin 8 is OUTPUT, and Pin 14 is Vcc.   If you have the halfsize
 parts then Pin 1 is either N/C or TRISTATE. Pin 4 is GND, Pin 5
 is OUTPUT and Pin 8 is Vcc.  These are easy to see if they
 operate.  Just provide power to pin 8 or 14, Ground pin 4 or 7,
 and measure pin 5 or 8 with a scope of frequency counter.  If
 you don't see any activity, then pull pin 1 high in either case
 to enable the TRISTATE output.
 If you could supply some of the numbers on the top of the 4 pin
 crystals, that may help identify them easier.

                                        Regards,

                                          Jim



On Tue, 04 January 2000, Ian Smith wrote:

>
> I have some crystals I pulled from old boards, but am unsure if they
> are any good.  Some were a bit, ahem, abused in the process. :-)
>
> Other than writing a program on the PIC that should run in a time
> period and timing it with a stopwatch with different crystals, is
> there an easy way to measure the speed of a crystal?  I have a
> multimeter that cam measure Hz but I am not sure how to hook it up.
>
> Also, I have some four-lead crystals.  The best I can tell is that there
> are two clock pins, a ground and a pin to turn the crystal on and off.
> I have however, been unable to use these in any PIC projects.. so must
> be doing something wrong.
>
> Thanks!
>
> --
> IanSmith@ncinter.net

jim@jpes.com