It has been rumored that the local AM station in my hometown was not dropping its power or changing its pattern at night, a clear violation of their license grant. Since the neighboring co-channel stations and the FCC don’t care about rumor or my “opinion”, I wanted a way of automatically logging the field strength of a broadcast station. This also paves the way for propagation studies and watching for band openings.
I had been eyeing the Silicon Labs line of receivers on a chip for some time but they come in a hard to work with surface mount package. Finally SparkFun Electronics came out with a board based upon the SI4735 chip, which does everything… AM FM Shortwave and Long Wave. It does RSSI (received signal strength indicator) as well as digital audio (not HD radio unfortunately) and RDS or RDBS. And its on an Arduino shield!!
I’ll say a few negative things about this shield…
- It did not come with pins to mate with the Arduino. Fortunately I had something that would work temporarily until I can get the proper ones in.
- The library code is riddled with “not working yet” comments. I have some work cut out for me getting simple things like -Get Frequency- working.
- The status response was coming back with all zeros. I found a couple solutions in the SparkFun comments, I had to add a delay, but the status response was still nonsensical. I found a thread in the Arduino forum describing a pretty serious design flaw.
So far that is all I’ve found -wrong- with the board. I was able to tune around the FM and AM bands and surprisingly, was pulling in a station in New Haven, Connecticut, about 11 miles distant, with no antenna, just the traces on the board! See the board in action and a map of the path below.
So with that said, I think I’ll make a proper 3.3v to 5v converter for the D12 line and begin programming the board shortly.