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some tips on gsm/gprs modem?

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abicash

Member
Hi,
I want to develop a gsm/gprs modem with 8051 for controlling devices through SIM cards.can anybody share some resources or tips from where I can start off?
can this be achieved with 51 family (or advanced derivatives) ?
thanks in advance
 
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Papabravo

Well-Known Member
We built a device with an AT89C51ED2 and a Siemens XT55 GSM unit. The SIM card just lets you get on a particular cellular providers network. It doesn't do much for controllong devices. Can you elaborate?
 
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abicash

Member
Thanks for the concern.
I want to build the gsm unit or the modem which siemens or singtel or many others market.I understand that the sim wil just hook on to the carrier and some AT commands wil control say a relay through the siemens device..But its the device i m aiming at..
 

Papabravo

Well-Known Member
abicash said:
Thanks for the concern.
I want to build the gsm unit or the modem which siemens or singtel or many others market.I understand that the sim wil just hook on to the carrier and some AT commands wil control say a relay through the siemens device..But its the device i m aiming at..
The processor which runs the GSM modem is an ARM7 TDMI with a boatload of mermory. Tis a bit more than an 8051. Are you sure you're up to it?
 

RadioRon

Well-Known Member
abicash said:
Thanks for the concern.
I want to build the gsm unit or the modem which siemens or singtel or many others market.I understand that the sim wil just hook on to the carrier and some AT commands wil control say a relay through the siemens device..But its the device i m aiming at..

If I understand you correctly, you want to build the wireless modem that connects to the cell network. If you are starting from scratch it is a huge task, not really feasible for one person to do. You have to write a GSM protocol stack and a user interface engine. You have to get this to run on a processor, then design and build a GSM radio transceiver and code to control the transceiver, all to make it work as a cell phone. Then you have to get the whole thing type accepted in each country you want to sell it in. Then you have to also get it certified by each carrier you want it to work with (and there are many of these). These certification processes are lengthy and expensive. If you are only doing it for yourself, I don't think you will be able to get it to operate with any carrier's systems without certification.

It typically takes a large team of engineers to build all of this and probably the total effort is in the dozens of man-years and costs a few million dollars when done by a cellphone company like Siemens.


If, instead, you are like many companies that make GSM phones, you don't start from scratch. Instead, you license a chipset from another company that has already developed most of the code (there are several such companies). Once you persuade that company to sell you their chipset (they will be interested in how many tens of thousands you will be buying), you design a modem around this chipset and then go through all the certification testing. But even this amount of work is not a reasonable project unless you have a few friends to help you out. There are companies that can throw together a wireless modem or cellphone with a fairly small team of, say, 10 engineers.

(The SIM is just a memory that holds your personal subscriber information, it doesn't do anything functional for your modem other than authorize it for use and provide some billing info. It isn't clear from your request if you understood this or not.)


If you choose to go ahead, you will need an instrument called a cell site simulator, also known as a communications tester to test your modem. The workhorse model used by many is the Rohde and Shwartz CMU200. Here is one on Ebay for a great price, only about 25% of the "new" price:
**broken link removed**

good luck.
 
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Papabravo

Well-Known Member
MAN!
The line of bidders for that tester is truly impressive.
The Siemens modem sure saved us a boatload of development time and expense.
 

RadioRon

Well-Known Member
Papabravo said:
The Siemens modem sure saved us a boatload of development time and expense.

I've done it both ways, from scratch, and starting with a module. The module way is a lot easier. You would think that the tradeoff is that the module will cost you more than you could build it yourself for, but surprisingly, since they make them in such high volumes, this is not the case. The real tradeoffs are size, a lack of design control, and not being on the leading edge on features.
 

abicash

Member
thx for the replies.thats really overwhelming.this seems a very high end project for me and our group of 4 engineers.We were hoping to start this with 51 or advanced (thats wat i asked in my initial post).If it needs an ARM core,then its out of question.Maybe I could use such a readymade modem in controlling devices,and give an advanced feature of internet connectivity :rolleyes:
 
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