3G Cellular Modem

[JosueReynoso]

My company is developing a vending machine which has to have conection to a server throuhg a cellular modem.

We already started the design of the electronics but since we have never worked with cellular modems we would like to ask for some advice before doing our research homework.

As far as I know there are 2 main ways for achieving communication, throug SMS and throug direct communication. And also GSM or GPRS can be used. We are thinking in using a wavecom modem. What is the best way to find all the needed information? Thanks

 

[MikeHalloran]

Ask the modem manufacturer?
Ahahahahahaha!
Sorry.

I have one cellular modem, provided by AT&T with a Windows XP driver which is itself clearly a shell around a collection of binaries provided by an amazing assortment of suppliers. It mostly works, but it has some clearly unintended behaviors that cause it to 'go off to see God' regularly.

The modem manufacturer also makes available a kernel level module for Linux, in several flavors depending on which kernel you're running. It's a lot more primitive than the AT&T/WinXP software, but it doesn't need a daily power cycle to keep it running right. It just runs.

This particular modem vendor apparently supplies executable binaries and compilable intermediates of some kind, but no source code that I could make sense of. ... and they're reputed to be one of the more cooperative hardware vendors. Apparently the cellular modem market is hotly competitive, and the participants differentiate their products by means of non-obvious control schemes which they do not share with anyone.



Mike Halloran
Pembroke Pines, FL, USA

 

[Comcokid]

Previous company I worked for (couple years ago) we use the Wavecom modem for battery operated fluid level monitoring. Worked great even though we had to wake-up the modem on a schedule (via MSP430 uP), connect, send a SMS message, wait a couple minutes to see if there was a returning SMS (setup and schedule info), then power down. Data was ultimately forwarded to our internet server allowing our customers to monitor or dispatch trucks as needed.

With a system consisting of many cellular modems that may be distributed over a wide geographical area, you need a 'aggregrator' - basically a middle-man who has premade contracts with all of the cellular companies and who handles the data to/from your modems and provides the SIM card setup for your data-only setup. Cellular companies are too focused on getting minimum >$50/month/voice customer, and the aggregrator carries heavy clout with the cellular companies since they are contracting 6/7-figures/month with the cellular carriers and can provide you with heavily discounted pricing for you data-only.

When you finish designing your device in North America, you will be required to obtain PTCRB approval for the cellular system to allow you to use your product containing a cellular modem (

http://www.ptcrb.org)

This is true even if you use something like a Wavecom. The last thing the cellular community wants is devices with flakey software/hardware/antennas that jams cellular channels with bad operation. PTCRB approval using a pre-made modem is about $20K to $40K. Companies that make cell phones easily pay over $200K to get their made-from-the-chip-level-up phone models approved. This is in addition to the standard FCC approvals for your own electronics.

 

[JosueReynoso]

Thanks for your kindly answers. Mike, sorry, I forgot to mention that we are building the project in a microcontroller (ATMega series). Comcokid, I will contact Wavecom thanks for your suggestion.

 

[VEBill]

Depending on your budget, you could plug almost any 3G modem USB stick into (for example) a CradlePoint router and then it would allow you to use wired Ethernet - if that would make things easier for you.

Such routers can be used with almost any 3G USB stick. And such flexibility might be useful if these machines are going to be used in different areas.

I used to own a CTR-350 ($100 - $150 price class) and used it with three different sticks and two service providers.

 

[itsmoked]

JosueReynoso; Make sure you compartmentalize you system's dealings with the modem. The modem models change just about as fast as shoe manufacturers change shoe models.

PTCRB approval using a pre-made modem is about $20K to $40K.

I'm surprised. I've never heard of anyone paying anything close to that or anything at all for that matter.

I think there are two levels. If you're using a modem module that plugs onto your board then you're in for the thrashing. But if you get the modem type that is essentially self packaged and you just talk to it with RS232, then you don't need to deal with the hassle. That's probably because there are smarts in the RS232 interface hardware that prevents the modem from entering some network crashing mode, regardless of what the user does. Of course the price seems to be much higher, often around $100 a point whereas a plug-on modem might only be $30.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[benta]

There are few points to look out for.

First, a GSM/GPRS modem is just that: a modem. You control it using Hayes/AT-commands.
The modem itself i just a PCB that you can mount on your motherboard. Due to antenna differences, you'll need a final FCC/CE whatever approval of the complete system.

Second, choose one of the big three as supplier: Cinterion, SimCom or Wavecom. They are bound to have the widest range of approvals.

Third, check that the supplier has successfully demonstrated that a certain modem/antenna combination passes approval.

Fourth, make certain that the supplier gives you a signed IP imdemnification. This is important, as the GSM/GPRS world is so full of patent crosslicensing etc. (there are at least 100 patents in there) that litigation is a risk. Certain companies will even sue end users if there is an IP problem.

Fifth, make certain that your carrier accepts the modem. Your module supplier should give you a list of carriers that have approved the modem in question.

Good Luck,

Benta.

 

[Comcokid]

itsmoked and benta bring up the low product volume methods of getting into cellular data. There are companies that make cellular modems - basically a 'black box' that you talk to with RS-232. These are fine if you are only going to deploy a few dozen for data collection as the cost/box is in the $150 up range. These companies have already obtained PTCRB approval for their box with it's antenna and internal software. These RS-232 boxes are marketed to users for ease-of-use and the users never encounter the PTCRB issues. But, if you need the box to operate slightly differently - forget it.

But, if your application is higher volume (you did mention Wavecom), you need to go with the cellular modules which you get for about $30 to $50 each (even less depending upon volume). Wavecom and other module makers have had successive generations of their modules as the basic chip sets have improved. As the models change, they update using the same basic footprint and connector, and similar I/O instruction set/control. Typically you need a little firmware change as their models change. Wavecom can put you in contact with aggregrators for their products (many of their distributors or reps do this function).

There are firmware things here also that the PTCRB get involved with - Once they approve your design, you're locked into the firmware version that Wavecom has at that time. If you upgrade to a later Wavecom firmware version in their modem, or newer Wavecom module, you have to do some retesting. Wavecom keeps a model current for about 4 years, but their firmware may update about twice a year. The cellular system and the Wavecom modules are not a hard-fixed system. Both make changes for new features, or as overall possible system issues need to be fixed.

The issues are a little different in Europe. There are major telecom carriers that control vast areas of Europe, and getting the approval of the carrier will allow broad operation. Orange is a division of France Telecom and typically getting their blessing is enough.

I can provide you a contact with the company I worked for previously if you are interested. They do have devices that might be adapted for your use, and do have all the back-end data collection and web servers for a complete business solution. They actually provide the remote cellular-based sensors that monitor the fuel tanks for the backup generators for many of the large cellular providers cell tower sites.

 

[benta]

Comcokid, excellent point on the firmware versioning. That is important and I'd forgotten that.

Your pricing on 3G modules is a bit optimistic. For GSM modules, the price point in volume (10k up) is at this point 20...25 $.
GPRS/UMTS modules are at 45...60 $ for fully qualified modules.

Again, I must stress the IP indemnification guarantee from the supplier (don't ask me how I know).

Benta.

 

[ektel]

Hello there,

I think that its a mistake to focus on 3G Modems because it will become obsolete when you market it, 4G systems has to be targeted now. But if it only for learning purpose then i guess you go for it.

http://www.ektel.com.np

 

[MacGyverS2000]

He's not making the new iPhone...

Dan - Owner

http://www.Hi-TecDesigns.com