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Mdcastle
12-03-2014, 08:29 PM
I'm looking at the application note for the datasheet on the LM393, and was wondering if the crystal oscillator would be easily constructed, or if this is getting into the realm of leads too long causing too much capacitance and it not working. Also, the data sheet uses a 100khz crystal, do I need to modify anything to use a more common 32768 crystal with these specs:
Load Capacitance: 12.5pF.
Equivalent resistance: 35KΩ.
Frequency tolerance: +20 PPM
I would then use a 4059 to get the exact frequency I want. Is there a guide or online calculator on how to use one of these?


http://www.ti.com.cn/cn/lit/ds/symlink/lm293-n.pdf

beowulff
12-03-2014, 10:12 PM
Unless you really want the excitement of building your own oscillator, I would recommend a "clock oscillator" like this:
http://www.digikey.com/product-detail/en/DS32KHZN%2FDIP/DS32KHZN%2FDIP-ND/420269

If you want to make your own, it's easier to use a inverter to drive the crystal, like this (http://electronicdesign.com/site-files/electronicdesign.com/files/archive/electronicdesign.com/content/content/63079/63079-fig1.jpg).

engineer_comp_geek
12-04-2014, 04:59 AM
Unless you really want the excitement of building your own oscillator, I would recommend a "clock oscillator" like this:
http://www.digikey.com/product-detail/en/DS32KHZN%2FDIP/DS32KHZN%2FDIP-ND/420269

I had exactly the same thought. I haven't used a discrete oscillator circuit like that in decades.

If you want to make your own, it's easier to use a inverter to drive the crystal, like this (http://electronicdesign.com/site-files/electronicdesign.com/files/archive/electronicdesign.com/content/content/63079/63079-fig1.jpg).

To expand on this a bit, this is called a "Pierce Oscillator" (named after its inventor). The wikipedia article for it has decent information about how it works:

http://en.wikipedia.org/wiki/Pierce_oscillator

This is a more detailed beginner-level description of a Pierce Oscillator (warning - PDF):
http://www.crystek.com/documents/appnotes/pierce-gateintroduction.pdf

While the wikipedia article does say basically how to calculate the values for the capacitors, the pdf article goes into a lot more detail about it and also explains the feedback resistor a lot better (including why it would be missing in the schematic that beowulff linked to).

You can google "Pierce oscillator" for more info.

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