GSM SMS communicator

[RodneyB]

I have Built a very simple panic button system and would like to know how I can build a circuit to add an SMS communicator onto it. I have considered purchasing a premade unit but all my web searches return results of Bulk SMS equipment and not a unit that I can pre program a message into and it will send it to one or a few separate cell phones.

A circuit diagram or a link to a circuit diagram or supplier would be greatly appreciated.

 

[dougy83]

You can get GSM modules from a number of places including Sparkfun (https://www.sparkfun.com/categories/68), ebay and dx.com

You could also use an old mobile phone (or a new one for that matter). If you use a module or an old mobile phone (e.g. some Ericsson or nokia models), you'll need a serial connection (from a computer or microcontroller) to instruct it to send the SMS. If you use a newer phone with iOS or Android, you can write an app to send the SMS (e.g. when the phone is powered up it can send the message(s)).

EDIT: Here's a cheaper module: **broken link removed**

 

[Wilksey]

On a side note, Dougy83 is correct, you can get GSM modules from places like SparkFun / Ebay, SIMCOM (SIM300 etc) and Telit breakouts are quite popular. Try and find one with a power circuit if you can as you will require a 2-3A supply if you ever want to connect to GPRS as it will peak at this level (module dependant).

If you wish to automate something like sending an SMS to a few phone numbers, then you will need to interface one of these modules, or a mobile phone, make sure that the SMS supports TEXT mode and not just PDU as PDU encoding is a pain for a beginner, grab yourself a microcontroller and you may need some level shifting and hook it up to the GSM module / phone and then grab yourself a copy of your phone or GSM module's AT Command set.

HTH

Wilksey

 

[dougy83]

I interfaced to an Ericsson brick phone to send and receive SMSes 10 years ago when I was certainly classified as a beginner (and using DOS Quick Basic - I couldn't even program in C/C++) - PDU mode was not painful to interface, IIRC it just required packing 7 bit data into bytes.

 

[Wilksey]

No it's not that difficult but if you are not familiar with bit shifting etc then text mode is easier, most support both and text mode requires just text and no packing, although I would suggest looking at the GSM alphabet if using special characters.

HTH

Wilksey

 

[RodneyB]

Thanks everyone for the assistance I have been looking at whats available and have found units ranging from US$9.00 to US$120.00 so need to see which is best suited for my needs.