“This was a triumph, I’m making a note here, huge success! It’s hard to overstate my satisfaction”
The reason I bought the Sparkfun SI4735 Arduino Shield last week was to graph and log a certain broadcast station’s signal strength to confirm or deny the “rumor” and “opinion” that they were not reducing power or changing pattern at night, a clear violation of their license grant.
I got this working tonight!! I am now collecting data and waiting for ‘sunrise’ to see if their power jumps up, and ‘sunset’ tomorrow, to see if there is a corresponding drop in signal strength.
So far the graph is filling nicely as shown below.
The code is far too messy to release at this time, and I still have a few bugs to work out, but these are the basic steps that happen.
- Arduino waits 30 seconds and then checks tuned frequency, received signal strength, signal to noise ratio and AGC value.
- Arduino spits a comma delimited string out of its serial port.
- A Processing script receives this string, parses out the data and writes it to a PHP script residing on this server.
- The PHP script writes this data to the mySQL database.
- A hapless internet viewer calls up a PHP script which reads the data out of the mySQL database and graphs it nicely using the Flot graphing package.
- . . .
It should be noted that I built an AM loop antenna for this project. It’s only 10 turns, I was getting tired and sore from keeping constant tension on the wire and flopping the cross around, but it works nicely. I want to add more turns, weather proof it for outdoor use and make it tunable.
I will post construction details and a BOM in a future update when I am happy with the design.
For now, behold the graphy goodness at http://w1xbs.com/flot/fieldstrength1.php