One of the few things cooler than an Arduino is an Arduino with a cellular shield. As you would suspect, this $100 shield from SparkFun gives an Arduino cellular capabilities, including the ability to send and receive text messages — and apparently the ability to place and receive voice phone calls, too. Tronixstuff has an excellent tutorial on getting started with the shield — I highly recommend it.
Here are some of my experiences getting the shield up and running with some basic, proof-of-concept sketches. I am in the Eastern US, and have had success using the AT&T network. If you are in another area and/or use another network, your mileage may vary.
First of all, in addition to an Arduino (a Duemilanove or Uno is recommended, although a Mega will work with minor tweaks) and the shield itself, you’ll need the following:
- A cellular antenna (helpfully also sold by SparkFun)
- A SIM card which is not locked to a particular handset (more on this below)
- A relatively high-current 5-volt power supply (since the Arduino’s regulator isn’t rated for the amount of current — up to two amps — the shield can draw.) You can, however, backfeed the Arduino from this 5V supply quite nicely.
- (Recommended but not technically necessary) a case to secure the shield and antenna.
The 5V power supply was easy enough, for the time being — I decided to just use a bench supply for testing. The antenna was easy, too — I picked it up from SparkFun at the same time as I bought the cell shield. Next, I needed a working SIM card. I bought the cheapest model of AT&T “Go Phone” that I could find at the local Target. $19.95 for a cell phone — a little pricey, but I might be able to repurpose it or some of its parts.
I activated the Go Phone and associated SIM card easily enough, and chose the $2-per-day unlimited calling and texting plan. (I figure that on any given day, I’ll either use the network a lot or not at all.) Texting and phone calls worked fine from the included Go Phone. When I put the SIM card in to the cell shield, connected the antenna and power, and ran through the configuration, though, I hit a problem — the “+SIND 7,” or “Emergency calls only” error. A quick search later, I found out that this was due to the GoPhone SIM cards being locked to the GoPhone handset for six months.
This was not acceptable: the whole reason I bought the Go Phone in the first place was to get a working SIM card for the shield. I made a trip to the local AT&T store and explained the situation. After some misunderstanding (the sales staff out front didn’t seem particularly tech-savvy and thought I was asking them to unlock an iPhone or something), they gave me a replacement SIM card — one not locked to a particular phone, this time. I swapped the new card in, re-tried the SMS examples in the tutorial, and it worked!