exxos's Atari, Amiga & retro forum

I thought this ClockInACan project would be a great way to create an oscillator alternative for my ST projects.

https://github.com/schlae/ClockInACan


So I created a test one with a crystal from an old ST. The crystals are labelled as 32.084988mhz so this was a good use for these old crystals. Or so I thought...

I have set up test bed and now tested all of my crystals. They are all running in the ClockInACan as around 10.6mhz!!

Every other crystal I tested runs at the Mhz on the crystal so I know the ClockInACan is working fine.

Clearly these Atari crystals need the additional circuitry to generate a 32.084988mhz output to the Shifter chip. It looks like the clock from these has a 3x multiplier to get the output clock in the ST. The crystals are NOT 32.084988mhz as they are labelled or at least all the ones in this photo are not.

Rest assured that these are proper 32.xxx MHz crystals. If you put your scope to the oscillator circuit in an ST, you can see the crystal oscillating at 32.xxx MHz. It's quite common to operate crystals at their overtone frequency, e.g., ≈3xfundamental, i.e. 3x10.6xx MHz. See here: https://www.jauch.com/blog/en/how-does- ... artz-work/

It's just your "clock in a can" circuit that apparently excites the crystal at its fundamental frequency.

Thanks, yes this makes sense.

PS: The datasheet of the IC used by the "clock in a can" confirms this: "The NJU6311 is a fundamental quartz crystal oscillator".