Cell phone communication via serial link

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Cell phone communication via serial link

Postby dbekker » Fri Oct 07, 2005 7:26 pm

I am a senior at Rochester Institute of Technology and I need some information on linking up a cell phone to a microcontroller for my robotics project. The idea is to connect a CDMA cell phone (Verizon or Sprint) to an HCS12 microcontroller via a serial link (RS232). Hopefully, this will allow me to send and receive serial data from the microcontroller remotely. After reading through the site and the C++ code for weather BBS project, I have this question. After connecting to the cell phone and having the microcontroller issue the appropriate AT command to answer the call, how easy/difficult is it to send/receive serial data? Is it as simple as writing to the serial port of the microcontroller (and the cell phone connected to the serial port sends each individual characters to the other end, like a direct link through hyperterminal)? Or is it more involved with more AT commands and encoding/decoding data streams from/to the cell phone? I just want to know how involved this might be, whether it is worth it, or maybe I should just get a pair of inexpensive wireless modems (like 433MHz Long Range Radio from HAC). It would be really nice to have the unlimited range with the cell phone as the modem.

Thanks.
Dmitriy Bekker
Computer Engineering (BS/MS)
Rochester Institute of Technonolgy
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Postby jayjay » Sat Oct 08, 2005 2:57 am

Which model of the phone are you planning to use, I have used Siemens C35 which has a serial link and takes in AT commands. Though I did not interface it to an MCU, I hooked it to a PC's serial port. I should say this should be no different if it were to be hooked to an MCU.

I would also suggest you might look into a GSM modem like SonyEricsson GM29, it has both GSM and GPRS connectivity and fully controllable via an UART using AT commands. I think SparkFun also sells a GSM modem from a different manufacturer.

HTH
Jay
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Postby dbekker » Sat Oct 08, 2005 8:38 am

Well I don't have a model in mind yet, but I am open to suggestions. I was planning to switch my provider soon from Sprint to Verizon, but I just looked at Cingular and T-Mobile plans and they don't look all that bad (T-Mobile doesn't seem to have very good coverage). I'd like to get a phone that I can connect to the MCU and also use it as my personal cell phone. That would be the cheapest solution, where I would not need to buy a modem. So if you know a good Sprint, Verizon, Cingular, or T-Mobile phone that can take serial commands from an MCU, please let me know. I think I would prefer a Verizon phone just because that's what most of my friends have (free calls). It would also be good if the provider did not charge all that much for data calls. The Siemens phone you mentioned, is that a GSM phone? If so, that means it works with Cingular or T-Mobile, right? Is there a high charge for data calls?

Thanks.
Dmitriy Bekker
Computer Engineering (BS/MS)
Rochester Institute of Technonolgy
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Postby jayjay » Mon Oct 10, 2005 1:45 am

Hello

Sorry, I do not live in US, I reside in S.E. Asia, so I am not sure what type of network the carriers you mentioned support. The Seimens I mentioned is a GSM 900/1800 phone, I have also used Nokia GSM 6210, 7110 earlier, I doubt these models are avilabe now, but I think they may be available in Ebay.

HTH
Jay
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Postby vz » Mon Oct 17, 2005 3:01 am

If cell network allow to make data call and phone support data mode calls, you only need to know modem's initialization string. almost all cellphones support that.
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Siemens MC75 GSM Module with Serial Connection

Postby tomb » Tue Oct 18, 2005 3:45 pm

If you want a straight forward Serial Connection to your weather device use the Siemens MC75 with the DSB75 development module (has DB9 serial connection). You can use Windows HyperTerminal to establish a data connection and figure out how you want to control your weather device. You can then write your C++ code based on that.

If you are concerned about GPS info (since you will be building a weather device that may get moved around) you should check out the Siemens XT55 Development Module.

I know this isn't for a CDMA phone, but GSM is more widely used worldwide.
Tom
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