| ??? 09/07/09 12:27 Read: times |
#168770 - You do not *need* 2 modems Responding to: ???'s previous message |
Anil Gupta said:
(1) You will require GSM Modem at both transmitter & receiver end. Not true. You obviously need a GSM device at the mobile end, but you do not need one at the "fixed" end If you have only a (very) few mobile units, a GSM device at the "fixed" end may be adequate; but for any significant number of mobiles, you should look to a network connection over the internet. Both the modems are identical in spec. Not at all! The whole point of the GSM Standards is that any compatible device can inter-work with any other compatible device. (2) You need to put Local Cellphone service provider (like Aittel, BSNL ect) activated SIM card in both (sic) the modems Of course - you cannot use any GSM service witout a valid SIM and service subscription. Be sure that the service you get provides the features that you require, and that your usage is in accordance with its terms & conditions... (3) GSM modem send & received data via a simple RS-232 serial port Beware! The term "modem" can be used quite loosely! I would, indeed, take the term "modem" to mean a boxed device with RS232 interface - although modern "modems" (like everything else) are increasingly using USB instead of RS232... GSM "modules" are also available which provide the same basic functionality, but without all the extra "support" of a nice case, power supply, convenient connector, etc, etc... These "modules" do not use RS232 - and often don't even use standard 5V or 3V signal levels. Therefore, you must read the documentation very carefully indeed to be sure that you fully understand precisely what you are getting. (4) You will receive Vehicle Location co-ordinates also via serial port Although this is most likely, do not just assume it - check the documentation carefully. (5) So at Vehicle end yor require MCU with 2 serial port - one for GPS receiver & one for GSM modem You should also give careful consideration to at least 1 more serial port for debug/diagnostics... (6)You will receive GPS co-ordinated on GPS serial port See above (You can dowload these command by searching GSM AT Command set) Be sure that you have the specific command set documentation for the particular device and version that you are using! (7) GSM modem at receiver end will receive SMS with GPS Data. As a GSM device, it will receive any and all SMS messages that are sent to it - be sure that your application can tolerate receiving messages sent "accidentally" by other users; eg, to a wrong number... Note that SMS may be a very expensive way to send this data... Tn be these SMS can be read on PC serial port using very simple appl program written in C or VB That depends on what you consider "simple". You can, of course, choose any language that you like! (8) For displaying vehicle location you have to use google maps application library available free for non comm use. No, of course you do not have to use Google Maps! |
