Evening all,
Months ago, I bought several picPET's from Tom Van Baak:
<http://leapsecond.com/pic/picpet2.htm>
Plan was to set up a power line phase measurement system using my Z3801
GPSDO as the 10 MHz input. Life intervened...and finally got back to
that project today.
I decided to do preliminary "playing around" to make sure I got
everything working right before I hooked it up to the Z3801 and a
transformer that would sample the line frequency. Tom included a nice
little 10 MHz oscillator unit, so I got to work using that as the 10 MHz
reference...and searching around for something to use as an event pulse,
I found a GPS unit that had what I suspected to be a 0.5 PPS output.
(two birds, one stone!)
The collection device was to be a Raspberry Pi computer as they are
simple, cheap, and in my experience, work pretty well.
First thing to do on the RPi was to disable the serial console so that I
could use those UART pins as the serial input. There are a number of
automated way to do that online.
Second thing to do was to get serial into the RPi and display it. Found
another script to do that online. Initially the output from the picPET
was garbage, but thankfully I was using a pP05 and pulling pin 4 high
made the text readable.
Third thing to do was to get some sort of serial logging program. I
found one called grabserial. <http://elinux.org/Grabserial> Grabserial
is nice because it has a lot of options that will make it nice to use in
an automated fashion. IE: I can tell it to collect for "X" seconds,
record to a file, then terminate, plus log the system clock for giggles.
Grabserial gave me fits! Turns out that it doesn't pass the command
line switch for the RPi serial port somehow, but editing the source to
reflect /dev/ttyAMA0 as the serial port made it work. (I submitted an
issue on github to the development team to see if I'm an idiot or if
this is a real issue)
Fourth thing was to figure out how to name files using the time and date
so I don't have data file collisions. Studying the date command yielded
an answer:
now=$(date +"%Y-%m-%d__%k-%M-%S")
python grabserial.py -e 30 -t -T -v -o log.$now.log
This names the log file "log.YEAR-MONTH-DAY__HOUR-MIN-SEC.log" which is
mighty handy.
Next up - setting up a chron job to run the above once per day so I get
one data file per day, keeping the file size manageable. Also need to
get Samba working so I can pull the data files off the RPi onto the PC
for manipulation. :)
thanks much and 73,
ben, kd5byb
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