[time-nuts] Homebrew frequency counter, need help

Li Ang lllaaa at gmail.com
Fri Nov 28 08:04:27 EST 2014

The TDC-GP22 is the best choise for me at the moment. Since I am not a
hardware guy, simplicity is important. It's very cheap in China(About 3$
for each piece ).

TDC-GP22 has 2 modes and 3 trigger inputs (start, stop1, stop2).  The min
time between start and stop is 3.5ns. max time is about 2.4us.(0 to 2.4 us
between stop channels).
Time resolution is 90ps, or 45ps in double_res mode(1 stop input only), and
22ps in quard_res mode(1 stop only)

The biggest problem I met:
If you trigger start first, 100ns later stop1, another 100ns later
stop2.Get the result of stop1-start and stop2-stop1. You will find
stop1-start is very unstable(+-2% level) and stop2-stop1 is stable(+-0.1%
level ). Dont know if it's my problem or theirs.

Here is the configuration of it (the document is very bad, took me 3 weeks
to play with these 6 registers to get it work as I expected) and schematic.
    Register_0 = 0x00c42700,
    Register_1 = 0x19498000,
    Register_2 = 0xe0000000,
    Register_3 = 0x00000000,
    Register_4 = 0x20000000,
    Register_5 = 0x10000000,
    Register_6 = 0;


2014-11-28 0:20 GMT+08:00 Tom Van Baak <tvb at leapsecond.com>:

> Your project sounds wonderful. The TDC-GP22 has been mentioned only a few
> times over the years and I keep waiting for someone to post actual results
> from this chip, or better yet -- schematics, photos, and source code.
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