[Test-Equipment] Chinese DID Crystal Tester Question

[David DiGiacomo]

On Wed, Apr 26, 2017 at 7:11 PM, Doug Hensley <w5jv at hotmail.com> wrote:
> I put together one of the red pc board kits that you see on the e-place.  Thing has 5 seven segment LCD digits, a 9V input socket, a small crystal socket for the tiny long wire crystals you see around, and a function switch which, when pressed, displays "sub", "add", etc.  Haven't figured it out.
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> The main issue i have with the unit is it seems to read left to right, from mHZ to kHZ and then rounds off or truncates the decimal or last digit so that you still don't know exactly what frequency it is and worse, can't tell how far off an old crystal is.
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> Has anyone found a function or truth table for these things?


Assuming you mean LED rather than LCD, here are a couple of slightly
different manuals:

http://img.banggood.com/file/products/20141231030459SKU184055%20frequency.pdf
http://img.banggood.com/file/products/20160817023551SKU360318.pdf

BTW, the crystal oscillator circuit used doesn't have an especially
wide range.  With the supplied capacitors, it's erratic with crystals
below about 4MHz.