Electronic – Understanding crystal resonator symbols – which one is 24Mhz

crystalfrequencyfrequency-measurementmeasurementoscillator

So, I'm in need of a 24MHz crystal to drive an AVR microcontroller. I've got some crystals that I've desoldered off some old, useless equipment. I've found three crystals that have '24' on their packaging:
HC 24.00
TXC 24.0NQ4L
24.00R4L

Google search turned out nothing, so I don't know whether any of these is 24MHz, or 2.4MHz, or some other values. From what I've managed to find, 24MHz have three 0's after the dot, but I couldn't find if 2.4MHz quartz ones have only two 0's or not.

I don't have a counter to measure how many ticks these can generate (too expensive :/ )

So, to expand the question a little bit, as I have more crystals in my collection: How to find out, without googling, looking only on the number on the package, how many Hz's are there?

Best Answer

The decimal point on crystal oscillators or crystal resonators is typically at the millions place or less often the thousands place, in hertz. The number of digits after the decimal point does not affect the frequency.

Thus, a 24 MHz part would be labeled 24.00 or 24.000, a 2.4 MHz part would be labeled 2.400 or (not seen this yet, but it is possible) 2.40.

A 32768 Hz crystal would be labeled 32.768 - those are common for RTC applications.

Other than 32.768 and a few other low frequency crystals used for very specific purposes, it is almost always a megahertz number marked on the part.

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