
GPRS Shield V1.0 - steeples
http://www.seeedstudio.com/wiki/GPRS_Shield_V1.0
======
danellis
I've used modules like this before (including the SIM908, which is like the
SIM900, but with GPS too). The biggest pain is that they only support AT
commands as a protocol. It's very difficult to work with reliably, especially
in a memory-constrained device. Whenever you issue a command, you need to
check the next line to see whether it succeeded or failed, but the next line
might be the response, or it might be an entirely unrelated unsolicited
response (an asynchronous notification). You end up with either a complicated
state machine or having to treat every command specially.

Even synchronizing the commands and responses is tricky, because you have to
send an 'AT' and wait for an 'OK', or if you didn't get one, send an 'AT'
again. Then when you get an 'OK', is it from the first AT or the second one?
So you have to spend a second eating all the data comes in before you can
start sending commands for real. It's all so... ugh.

I'd love for someone to implement a well-thought-out binary protocol as an
alternative.

I see the example code give here just cheats and waits 100ms for each command
to happen, then assumes it was successful and moves on to the next.

~~~
revelation
The problem is that there are very few companies making baseband chips, and to
say that they do not care, at all, about hobbyist applications, would be the
understatement of the year.

As it turns out, even your smartphone is probably right now talking AT to its
baseband processor. If you get one of these mobile surf sticks, it's probably
a virtual COM port and the software on your computer is giving AT commands. As
horrible as that sounds, it is the standard they use.

~~~
danellis
I always had this secret hope that the AT interface was a translation layer on
top of their sensible protocol (kind of like, say, x86 on top of microcode),
and that one day someone would have the bright idea to just expose the
underlying one.

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mslev
The link to buy it lists it as discontinued. Here is V2.0, which is available!

[http://www.seeedstudio.com/depot/gprs-
shield-v20-p-1379.html...](http://www.seeedstudio.com/depot/gprs-
shield-v20-p-1379.html?cPath=132_134)

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spiritplumber
One thing you can do is get a microcontroller that does USB host, get a
cheapie android phone online, and wire it up that way using ADB.

I wrote a library to let a Parallax Propeller do this (it will be more power
hungry than, say, an IOIO board, but it can give your phone 8 serial ports
rather than just one).
[http://obex.parallax.com/object/116](http://obex.parallax.com/object/116)

Economies of scale mean that a low end android phone costs about as much as
this shield.

~~~
swah
I suppose you can also use the GPS?

I always forget these kind of solutions made possible by cheap phones. The
other day someone suggested that a cheap phone is a great alternative to GPS
car tracking systems.

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hoopism
So for those who may have seen the BTTN post (100 dollar cell network enabled
button) you now know the dirty secret. You are this shield, and arduino and
60c away from building your own.

~~~
kenrikm
By the time you purchase the Sim900, Arduino and make a case you would be
about $70 - 100.

~~~
hoopism
You can get a barebones arduino for around 3-5 dollars. Shield (without any
price comparison shopping whatsoever) is 49 bucks
([http://tronixlabs.com/arduino/shields/gsm/sim900-gsm-
cellula...](http://tronixlabs.com/arduino/shields/gsm/sim900-gsm-cellular-
shield-for-arduino/)).

Siemens has an arduino compatible GSM module for 29.99
([http://www.sainsmart.com/siemens-tc35-sms-gsm-module-
voice-a...](http://www.sainsmart.com/siemens-tc35-sms-gsm-module-voice-
adapter.html?kpid=13_en)).

So 33 bucks and a free "That was easy" button from staples and there you go...
that's at single unit price.

BTW, for vast majority that is likely beyond their capability... so maybe 77
bucks is worth it? I dunno.

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2close4comfort
now this looks like it might be just thing for the SMS gateway I was building
for nagios

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franciscop
They just copy/pasted the wiki engine, it's even showing "Wikipedia, the free
encyclopedia". Looks like a really bad job. However, the Shield looks really
neat and worth it.

~~~
duskwuff
Er, what? That page doesn't say "Wikipedia" anywhere on it. It is running
Mediawiki, like Wikipedia, but that's free software; it's _supposed_ to be
used by other sites!

~~~
franciscop
Below the top-left language globe I can read "Wikipedia" clearly. I agree
about Mediawiki, just not about keeping the same image (;

~~~
wolfgke
On my laptop at the top-left corner there is a "seeed wiki" logo and no globe.

~~~
soneil
He's not crazy. On my phone, I see the stock wikipedia template - branding and
all (including the globe logo top-left). On desktop, I see the same content
but with seeed's theme.

So it looks like a straight rip (on mobile), but more likely someone's just
skipped a step or two with the branding.

