Alarm / Monitoring - SMS Texting
With the wide availability of GSM, many products may benefit from SMS texting eg alarm / monitoring systems etc. Apart from web connectivity, some form of GSM device is needed to enable this.
The main interface used for GSM devices is via AT commands which is a standard request / response text based protocol. Using AT commands, it is possible to:
To integrate a GSM modem into a product, the costs are high because of:
As dedicated GSM modems are low volume and fairly specialised, they are relatively expensive due to market forces. Current GSM modems interface either via an RS232 cable or an internal, proprietary bus - to date, none have a infrared port. Because a GSM modem is inherently an RF device that is cable-coupled, expensive RF related EMC/compliance testing is required.
GSM Mobile Phone
As GSM mobile phones are high volume, consumer products, they are relatively low-cost and widely available - even second-hand.
Using the above design, with a proprietary data-cable, forces high-cost EMC testing - the controller, sensors and phone have to be EMC tested and approved. Because the GSM mobile phone is electrically connected, it forms part of the 'apparatus'.
Most recent phones have an IrDA compliant infrared port that may be used to enable low-cost SMS texting with minimal entry costs because:
Using the above design, with IrDA connectivity, allows minimal EMC testing - only the controller and sensors have to be EMC tested and approved. Because the GSM mobile phone is electrically isolated, it does not form part of the 'apparatus'.
Use of a mobile phone has several other advantages:
Re-use a product that would otherwise be scrapped - find a use for that old mobile phone !