This looks fairly neat. The "don't pay for a plan" part is a bit odd though... as far as I can tell you're only getting a year of free low-bandwidth data, and after that it'll cost you.
I queried the creator on kickstarter... he said $3 a month would be a worst case cost for said connectivity after your initial year is up.
Perhaps more importantly, he indicated that it would be possible to not use their server as a middleman, but that they need to get their analytics right before allowing that. Currently going through their server allows them to maintain sane data rates, apparently.
Personally, I couldn't find a one-off GSM data only SIM for less than $8 a month in my searches... even at multiple year prepay... so this sounds like a pretty good deal. I'm maybe more interested in just the cheap dumb pipe option, but really their "middleware" server does sound handy.
Since it's not clear from the description: do you pay for sending the data or not? If not, whose network does it use, and why are they allowing use of their network for free?
From the award levels, it looks like you don't pay for data per se, but you may be capped on the number of requests you can do per month, and maybe they offer increasing that cap for money. See this comment for some info about the protocol: https://news.ycombinator.com/item?id=6644515
I wish they would explain what this GSM shield does apart from the one year subscription and connection to their own platform?
There are several unlocked GSM shields and modules available with working libraries and tutorials for under $50, using the exact same GSM module (SIM900): http://dx.com/s/Sim900?category=499
None of those appear to be Arduino "shields", unless I'm not looking at them correctly? An Arduino shield is plug/play, whereas I would define a generic "module" as not.
It's not entirely clear in the description, but it sounds like data is sent to 2lemetry and then from 2lemetry it's sent to your server via POST.
It's too bad that you can't just send data directly, but I guess this probably means that 2lemetry will require specific structured data and will limit requests. They say the limit is TBD which is pretty vague and not very inspiring.
2lemetry is running an MQTT broker - MQTT is a standard protocol designed by OASIS for these sorts of low-power, low-bandwidth scenarios. It's a pub/sub system and you'll probably get away with a few messages per minute. I think the 2G hardware might be the limiting factor here.
> We are modeling data limits around scenarios where a sensor value is sent to an HTTP endpoint once or twice per minute. Expect final rate limits to be in that range. For specific questions on increased rate usage, please email us at info@2lemetry.com. Higher end plans are available.
Embedded development is not like web development. Sometimes these things might stay in a remote location sending telemetry data for a few years. I'm surprised, this being GSM, that they don't put a slot on the board as an optional add-on.
Are there technical reasons for this, or is it just designed to shut out competition?
APRS has been used for vehicle tracking for a while (it was first devised in the 80s).
It is dependent on independently operated base stations to relay data to the internet, and since all transmitters contend for the same frequency it may not be feasible in high-use areas. You also need a Ham technician license (35-question written exam).
I queried the creator on kickstarter... he said $3 a month would be a worst case cost for said connectivity after your initial year is up.
Perhaps more importantly, he indicated that it would be possible to not use their server as a middleman, but that they need to get their analytics right before allowing that. Currently going through their server allows them to maintain sane data rates, apparently.
Personally, I couldn't find a one-off GSM data only SIM for less than $8 a month in my searches... even at multiple year prepay... so this sounds like a pretty good deal. I'm maybe more interested in just the cheap dumb pipe option, but really their "middleware" server does sound handy.