GSM SMS Modules

[David_AVD]

Has anyone used a GSM SMS module for getting small amounts of data from the field?

The field unit will spend most of its time in sleep mode, only sending an SMS once a week or if something important has occurred.

I have one of the Siemens TC35 modules with Arduino shield on the way (eBay link) to test the concept.

Are there better modules out there?  It needs to be low cost and as compact as reasonably possible.

[David_AVD]

Just received the TC35 module and breakout board.  No documentation at all with it but I did manage to scrape up the board's schematic and layout elsewhere.

Was trying to talk to the module via the com port with no response at all.  Then I pressed the (unmarked) tact button on the breakout board and it springs into life.  Doh!

I thought I'd mention it here in case someone else gets this board and is wondering how to get started with it.   

[Riotpack]

I have attached a file of the commands for that chip. Try typing ATI from your terminal program and see what you get back. I will upload all the documentation when I get home from work, This forum limits my attachments to 1MB so I could only attach the first 100 pages

[Riotpack]

Here is a link to the complete docs for that board

http://1drv.ms/1jAMeP6

[David_AVD]

Thanks for the links.  I had since found them, but I do appreciate it.

Now I just need to grab a cheap SIM and see if I can send an SMS.

[Riotpack]

I got a similar module and just got a $2 prepaid Telstra sim and loaded $20 on the 365 day plan.

[David_AVD]

Can't see a Telstra one that's cheap with 365 day, but AldiMobile (Optus carrier) have one that's $15 with 365 day expiry so that will do for testing.   

[Riotpack]

I just got a $2 Telstra one from a service station. When I activated it, it asked which plan I wanted to be on.

[Harvs]

I'm using a SIM900 with TCP for a application that takes readings occasionally.  Same sort of deal, it wakes up, connects to the server and sends a packet, gets an ack back then shuts down.

This happens to be in a mobile application and the thing I've learnt is how much of a PITA an un-reliable data connection can be.  If reception is patchy the modules have a tendency to lock up at any given time and require a restart to get them to respond to AT commands again.  Given the reasonably complicated set of AT commands and timeouts in order to get the module online in the first place it ends up being quite long winded.  Results in quite a lot of code to handle just getting a few bytes of data reliably across the link.

[David_AVD]

What carrier are you using for your application?

[Harvs]

We've tried optus and telstra sims. Telstra has been considerably better in terms of coverage, but we've seen the same sort of problems when the reception gets poor.

You can get some good low cost deals on m2m plans through online resellers. Just Google it.

[David_AVD]

The local Telstra shop insisted that the $20 365 day recharge doesn't exist, so I ended up walking 2 shops down and getting a Vodaphone $2 SIM and $20 365 day recharge.

At least this way I can put that SIM into my regular phone (locked to Vodaphone) if I need to during testing.

So far I've got the TC35 to send an SMS as well as receive a few.  It's funny how such a simple task can make you smile when you get it working.

I can delete the SMS by index, but is there a way to "compact" the messages?  Say if I have 3 messages (indexes 1-3) and I delete # 1, I'd like them to be accessed as indexes 1 and 2 after I delete the message originally at index 1.

[han]

I use these one, it's a ready to use, and easy to debug in PC..http://www.multitech.com/en_US/products/families/multimodemgprs/

[David_AVD]

I need to work with the bare module as it needs to be a compact as possible and use almost zero power when not sending an SMS.

Nice looking off-the-shelf unit though.