Well it’s finally ready to share!
This counter is perfect for use used with DMTD systems to free-up more expensive counter for other work.
It’s called the ProTIC and Tom Van Baak designed the code which is available free at
http://leapsecond.com/prop/index.htm#proticPlease read the info on his page!
It utilizes the Parallax Propeller Mini and the FDTI friend.
The Propeller mini can be bought direct from Parallax or several other distributers
for around $24.99 and the FDTI friend is from Adafruit and others for around $14.99.
Some more details are at Tom’s page but the main ones for me are:
valid readings from (and including) 0.0 ns, up to 10.0 s
No dead time issues like the HP 53131/132 and SR620
Easily interfaces to USB or RS232
12.5ns resolution
10 digits
115200 baud
Low cost and minimal construction required.
Here are pictures of Toms prototype and also of the one I installed in my DMTD unit.
The bracket with the BNCs was just for testing and was removed prior to installation.
I configured mine for optoisolation and both RS232 and USB outputs.
Also here are diagrams of different hookup versions.
The 1K resistors on the inputs allow 5V inputs, also not shown are 50 Ohm loads on the
input BNCs.
Mine are switchable so I can either use 50 Ohms or not.
You might sneer at the resolution but remember the DMTD multiplication factor!
12.5 ns resolution equates to a 1.25 femtosecond resolution after the multiplication.
(10 Mhz with 1Hz offset)
The result is that the last few digits are essentially in the noise floor and not
important!
NOTE! THE DIAGRAMS SHOW PIN P15 AS THE SERIAL OUT, TOM HAS SWITCHED THE OUTPUT PIN TO P14 SO USE THAT INSTEAD!
I have run several weeks of plots with the ProTIC and several different Dual Mixer units
against very good Quartz as well as comparing HP 5065A units, and it has performed just as
envisioned.
The reset button is not really needed but it will reset the unit and output an ID string.
This is handy to check if you have the comm. set up correctly.
Tom programmed the prototypes for me and once I have a chance to program my first Propeller Mini
I’ll share the procedure for that.
Lastly here is a PIX of an old Sulzer linear phase comparator I got at a Gov. auction
in the early 70s. I used it in my early years of playing with frequency standards!
It would compare 2 100Khz signals and you used one of those old impact recorders to
record the phase. Years back I gutted it an installed a simple TIC circuit for DMTD use.
Worked great but the TIC developed problems and was not open source so it languished.
I repurposed it again with Tom's ProTIC and the Simple Dual mixer in the same chassis and
it lives again!
Cheers,
Corby