[time-nuts] Homebrew frequency counter, need help

Angus not.again at btinternet.com
Fri Nov 28 21:29:23 EST 2014

On Fri, 28 Nov 2014 21:04:27 +0800, you wrote:

>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;


That's very interesting. I've been planning to do a basic board with a
GP22 for a while - something like the acam evaluation board but with
some input circuitry, and plugged into a fast microcontroller board.
Could not decide what one, so I thought that an arduino-type board
would be the most flexible for now. I mainly just want to test it
until it squeaks.

Now that winter is coming and I've got all the bits, I'll hopefully
get time to do it. First job is QFN soldering. That should be fun.... 

I thought it looked like setting up the registers could be a bit of a
problem. The manual for the evaluation kit says that there are some
example setups included - I did wonder if it might be possible to see
that and other info if the software was installed and run, even
without their board connected, but did not try that yet. 


>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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