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hardware device for voltage measurement communication over GPRS back to the central server

Posted on 2004-10-20
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Hello Gentlemen,

I have a question about an application with GPRS, it's not related to programming, I must apologize if I am in the wrong section, please redirect me if I am wrong.

I have an application where I have a voltage measuring device installed in the field, for example, the desert.  The device is able to communicate data via a modem, and sends back the historical trend data.

I would like to use this with GPRS, and I would like to use GPRS so that it can send data using this medium back to my central server.  
Can you outline a few things that I will require and need to look at?  What will I need and what types of hardware will I need?  I believe this means I need a service provider for the GPRS, does this mean I need a cell modem.  And how will everything interface together to make it work.

I long for your answers.

Phillip
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Question by:phillipy
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by:jenmir
ID: 12363965
It sounds like you still have some research to do, and some big decisions to make. To get you started I'm providing some links and options on design.

First option is using basic cellular network data technologies. In the USA, you have a choice between two digital options, CDMA 1xRTT and GPRS/EDGE.  The analog version CDPD used to be an option but it's going away very soon so don't even pursue that one. Both digital types of networks have USA coverage, but neither has complete coverage in "the desert," which you mentioned above. If you're truly working in remote locations like that, cellular may not even be an option for you. Go to that desert location first and try to use your GPRS cell phone there - does it work? Do you have at least 2 bars of signal? Very important consideration.  

Anyway this first option involves an embedded system that has some modem interface, either PCMCIA or serial. Then you need to be really good at writing software: you'll perhaps be delving into API, writing software to drive an AT command set and figuring out your communications stack (TCP/IP, PPP, hardware). Examples of PCMCIA compatible modems are Sony-Ericsson GC82/83, Sierra Wireless Aircard family, Novatel Merlin series, etc. Some modems have embedded form factors, some are strictly serial port interface. Some have removable antennas - might be very important to you out there in "the desert." You decide what features matter to you. There are several after-market vendors of these types of devices hanging out on this forum, I'm sure they'll be glad to give you links to their sites for more info. Some manufacturer sites:
http://www.sonyericsson.com/downloads/GC8X_UG_RevC_EN.pdf
https://www.sierrawireless.com/SupportDownload/manuals_ac555.asp
http://www.multitech.com/DOCUMENTS/Collateral/manuals/S000293B.pdf  (always try to get an AT command set doc for these things)

Second option is to look at Machine-to-Machine type of system. Many of these stand-alone devices have modem-like features: they talk GPRS, CDMA, WLAN, RS-232, whatever you wish. They often have cool features like pre-written middleware to talk to your network, and some have internal communication stack built in so you don't have to worry about software that much. You do need to be a pretty good systems integrator to use these. On the surface, this option seems like a better fit for your application since it's expected to be in highly remote locations and if you're not much of a programmer.
M2M related links:
http://www.mobilein.com/M2M.htm
http://www.m2mmag.com/print/article.asp?ARTICLE_ID=115
http://www.ericsson.com/mobilityworld/sub/open/technologies/m2m/index.html?PU=m2m
http://www.nokia.com/nokia/0,8764,43167,00.html

Keep in mind with GSM type networks you need to visit your service provider to pick up a SIM card. Not necessary for CDMA though.

j.m. (who is not a Gentleman)

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by:phillipy
ID: 12367240
i like the first link, too bad it is only a short version

For the time being, let's work with option number 2.
Also I would like to award more than 500 points, pls advise how to do it.
------------------------------------------------------------------------------------------------------------------
so, the customer chose to use SMS, GSM
we will help embed the SMS capability to our voltage meters so that the meters in the field can send historical data back to the server via SMS.
now, i know I must purphase a GSM modem for the meter to dial out, is that correct?
the historical data log on the meter can get up to 1 MB, how will i send this large amounts of data via sms?  i understand the limit is at 160 bytes.

now then i must choose a carrier service provider that supplies sms.


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jenmir earned 500 total points
ID: 12372536
BTW the documents you most desire from the  modem manufacturers are AT command sets, and API (if they exist). Sometimes you cannot find them on their web sites and must go through a technical person to get them. But at least AT commands should be available. Read the AT set and see how rich it is and what kinds of features are offered. Read the SMS section and find out how much of the SMS command set is implemented. You'll probably also find a separate GPRS section in case you decide later SMS doesn't meet your needs and you need a more powerful data transfer capability.

Remember that SMS stands for "short message." It is ideal for very short communications only, and the reliability is not guaranteed - it is not supposed to be truly real-time. When you queue an SMS message up for delivery, the system may send it immediately, or after 1 hour... or perhaps after an even longer time period if the system tries repeatedly and cannot send the message through. How important is throughput and reliability to you? If you KNOW that you're going to have to send 1MB chunks at a time, and send them up quickly, SMS is not for you.  

The vast majority of GSM carriers support SMS - just ask. (Many carriers simply call this service "text messaging.") They'll probably have detailed service plans and several options. Compare various carriers in your area if there are more than one. You can probably get something like a package where you get x number of free messages per month, or you can pay as you go per message.  SMS is not considered 3G service - it's too primitive for that and too slow.

Many GSM carriers also support GPRS and you can pay per Mb or can purchase unlimited transfer. Unlimited GPRS in US is $80/month at most carriers.  Sounds like you  haven't decided for sure yet. Buy a modem that supports all GSM bearer services including GPRS and SMS. I'll bet though that SMS will not suit your needs in the long run - you'll need faster and more reliable 2.5G services like GPRS or 3G like EDGE if you're talking Mb transfers here.

Regarding your question on points, the answer can be found in the FAQ here: http://www.experts-exchange.com/help.jsp#hi76

In the USA, carriers tend to be either GSM or CDMA, but not both. It is not hard to find out which is which. Major GSM carriers are Cingular (now merging with ATT Wireless) and T-Mobile. I don't recommend Nextel since they have no plans for 3G capability and you might need it going forward. For help deciding on a carrier, you may wish to monitor the following forums:
http://forums.wirelessadvisor.com
http://www.howardforums.com

Best Regards and good luck
j.m.
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by:imarshad
ID: 12378393
>>the historical data log on the meter can get up to 1 MB, how will i send this large amounts of data via sms?  i understand the limit is at 160 bytes.

Yes the limit is 160 bytes......and I will also suggest you to go for GPRS......But if you donot have a PC at the remote site which is more likely and you are going to connect the GPRS modem with a Microcontroller then I will *strongly suggest* you to think before you go for GPRS....You will need a GPRS modem with builtin (TCP/IP, PPP) stack...... and even programming of such a modem from a microcontroller is not easy......Maybe connecting to the GPRS network is easy but tranferring data might not........

One other option that you have is to use *data call*....It is the functionality of GSM.....also called CSD (circuit switched data)......In this you will only need to have a GSM modem with which you can call any remote location Data transfer rate is mostly 9600 kbps.....Maybe consulting your GSM/GPRS provider will be better for you as they will give you the rate and availability of these things......

Imran
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