1. Home
  2. Embedded Programming
  3. Using Cell-Phone as Modem to Xmit Data From Remote non-Windows Devices ?

Using Cell-Phone as Modem to Xmit Data From Remote non-Windows Devices ?

I need to use cell phones to return remote data from envionmental monitors. The monitors will NOT be running Windows or Linux or any OS (they're PIC-based). The idea is to use the cheapest, dumbest possible cell phone with a serial or USB plug as the modem.

Dial-out can be done by programming the proper commands into the PIC - assuming the manufacturer uses an 'AT' command set or something similar. Dial-IN would be nice, if the phone produces some signal on its buss that can tell the microcontroller "I'm getting a call - turn on and send your data". If I could dial to the devices, a good old program like PROCOMM would serve to collect the data.

Internet capability is NOT needed or desired. Even a 300 baud connection would serve my purposes. The devices won't be collecting THAT much data each day. Even ten seconds at 300 baud would do it - and I wouldn't have to pay for internet access.

I've looked around on the web but there's a serious lack of focused "how to" articles on this subject. I can't tell if there's a specific kind of phone I need, CMDA, GSM or whatever. Everything I see assumes you're using a Winders or Mac to operate the modem.

Has anyone come across phone-modem stuff more appropriate for low-end embedded applications ? Money IS an issue here, power consumption IS an issue. I'm not going to bolt an old Winders laptop to 30 remote sensing stations just so I can make the phone work. A PIC, some sensors, a battery, a solar cell, a dirt-cheap cell phone ... that's the very basic package I'm trying to create.

Any pointers or links will be greatly appreciated.

Reply to group.

Reply to
Luminoso
Loading thread data ...

In article , Luminoso writes

RI or Ring Indicator line can be used if it is available to wake up your system. Otherwise you can use the interrupt line from your UART chip to wake up the system.

--
\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\
\/\/\/\/\ Chris Hills  Staffs  England     /\/\/\/\/
/\/\/ chris@phaedsys.org      www.phaedsys.org \/\/\
\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/
Reply to
Chris Hills

That may be availible on older phones with a serial port - but I think even those serial ports were rather limited in what signals they provided. Most newer phones have USB instead, so if there's a RI signal it's not going to be availible on that. Maybe one of the other little pins on the phone ? I'll have to try and get really detailed specs on a few of these phones, if I can figure out which ones will serve my purposes.

Reply to
Luminoso

we have worked with a siemens GSM cell , if I remeber well it was a T35 or something similar, mostly identical to the standard part but in a rugged enclosure it work as a 'standard hayes' modem in data mode ( with some extension in AT commands for system management )

the cell is actually connected to a data acquisition station and we are able to talk to him trough the hyperterminal

here in Italy the only problem was ( is ? ) the use of a special contract from the cellular operator, not the standard voice contract but a 'data contract'

Reply to
mmm

In article , Luminoso writes

The other alternative is to use a GSM modem phone. These are cheaper than a normal mobile and do have a serial port not USB. The problem with USB is you are going to need a USB stack... this starts to get complex compared to a serial port.

--
\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\
\/\/\/\/\ Chris Hills  Staffs  England     /\/\/\/\/
/\/\/ chris@phaedsys.org      www.phaedsys.org \/\/\
\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/
Reply to
Chris Hills

My throughput needs are SO small that GSM is not required. Ordinary voice-quality transmission ought to be adequate. As I said, even 300 baud is plenty quick. I'd be downloading about 100 bytes twice a day from each station.

But I need to find someone who's made it all WORK before. I don't know enough about cell phones or moving data over them.

Reply to
Luminoso

the module that I am talking about have a 'standard' RS-232 connection you only need to connect to your device and insert the SIM ( perhaps you need to do some configuration trough AT commands before first real use)

the real name of this cell-module could be TC35

Reply to
mmm

I wouldn't bet that even Bell 303 FSK will make it through a modern (digital) mobile phone's codec in a usable way.

And you've verified that 300 baud FSK works through digital mobiles?

I've done it but it was with a bag-style AMPS phone that had an add-on RJ-11 "phone-jack" module into which one plugged a regular modem. That add-on module provided dialtone for outbound calls and a ring tone for inbound calls.

My guess is that a GSM modem module is going to be far simpler and easier than trying to push analog modem signals through a digital phone (and you don't have to have an external modem). I've not done the latter, but I've never heard about any attempts that worked well.

--
Grant Edwards                   grante             Yow!  Look! A ladder! Maybe
                                  at               it leads to heaven, or
                               visi.com            a sandwich!
Reply to
Grant Edwards

I've got a compiler for PICs that will, allegedly, do USB. Haven't tried it though.

Reply to
Luminoso

I have fears that it won't. May be JUST enough delays in the system to foul up things.

Nope. I'm still at the start of the project.

Nice - but analog networks are all but dead now.

I agree that it's probably easier, given the way the technology is evolving. A valid concern however is COST. I'd have to buy a 'data' service for each unit and, multiplied by a few dozen units, we're talking quite a bill each month. I'll have to check with Cingular to see if data service can be had using a 'phone card' rather than a regular monthly account. 99.9% of the time these phones will NOT be in use, so why pay for it ?

Oh well, maybe the monthly bill wouldn't be as shocking as the huge up-front bill for dedicated data transmitters with a 25 mile range. Those need FCC licences too. My goal is "AFFORDABLE remote data-collection" for those put off by those expensive turn-key solutions. $600 for a GSM cell modem (RabbitSemi)... right ... I'd like each station to cost $600 total. $999 may be more realistic ...

In a few years, PDAs and cell phones will have merged entirely. This will give us a CPU, Winders Mobile and USB or bluetooth for reading data-collection hardware all in one package. For now though, a Blackberry will still set you back a bit, as will the other PDA-Phones.

Reply to
Luminoso

Verizon has a low-speed "dial-up" data service (14Kbps) that doesn't require a "data" contract -- it just costs minutes. I don't know if other carriers have a similar feature. You can use it to dial-out to Verizon's "ISP" number, or to dial out to any body else with an analog modem. I don't if it supports incoming data calls.

--
Grant Edwards                   grante             Yow!  I'm not available
                                  at               for comment...
                               visi.com
Reply to
Grant Edwards

Ah HA ! Useful information indeed ! That's four times the speed required ... and cheap if only the minutes count. I'll check-out Verizon. Thanks.

Reply to
Luminoso

Oh, I should have mentioned that it's an "unofficial" feature. It isn't mentioned anywhere in the brochures, on the web site, on in the service agreement. If you call support they'll deny any knowledge of it. So, if it doesn't work (or they shut it off), you're out of luck and will have up pony up for a data plan.

That said, I've been using it off and on for about three years from various locations around the midwest -- both dialing Verizon's ISP and my own.

The latency can be pretty large compared to landlines, so be prepared for that.

--
Grant Edwards                   grante             Yow!  Kids, don't gross me
                                  at               off... "Adventures with
                               visi.com            MENTAL HYGIENE" can be
                                                   carried too FAR!
Reply to
Grant Edwards

10 seconds/ 300 baud. Sounds like it would fit in a text message. I seen to remember seeing modules that would do that but .....

Googling embedded sms modem yields a few interesting hits.

You wouldn't have the immediate handshake if that was important.

Robert

--
Posted via a free Usenet account from http://www.teranews.com
Reply to
Robert Adsett

This question come up every so often.

Is there an off the shelf phone with any kind of data ?

The short answer is you _can't_ do this in the USA.

The cell companies do not want to go there. So they have a data plan to limit people from doing data over their networks.

Those who are willing to pay can play.

The only cell phone I have found that is readily available are from:

formatting link

You can use you SIM card from various cell companies. But unless you limit you usage to a few call a month, they will shut you down.

I used CDPD on one project, but it was a real killer in cost. Now CDPD is dead.

Good luck.

If you find any good plans, please post again. I have been looking for years.

Donald

donhamilton 20002 AT yahoo DOT c o m

Reply to
Donald

And you don't get that with digital cellular phones. You did with AMPS phones: 300-3K with normal C-Message weighting (or whatever it was called with a noise floor that varied depending on signal strength). AMPS phones would easily handle a

2400-4800 baud modem with a good RF signal (which was much easier with 3W Tx power, real antenna(s) and a diversity receiver). I've not tried it, but I've read in several places that the codecs used by digital phones won't even handle Bell-103, let alone Bell-212 or higher.

But, the USB interface to cellular phones doesn't carry audio. The phone is a USB serial device and will easily support

230Kbps (if you're allowed the bandwidth on the RF link). The phone pretends to be a modem and handles the normal Hayes "AT" command set, but when "connected" instead of modulating an audio carrier with the transmitted data, it just packetizes it and sends it up the digital link instead of encoded audio (and the converse with receive). The OP said he didn't need to use a digital data service since "normal voice quality" would carry 300 baud FSK. With an analog mobile phone that's correct, but with a digital phone you don't get anywhere near "normal voice quality" (at least not by any telephony standards I've ever tried to meet "back in day"). With a digital phone you really have to use a digital transport mechanism. Everyting I've come across indicates that the codecs in use have such a low bit-rate that even 300 baud FSK won't make it through. 
--
Grant Edwards                   grante             Yow!  WHOA!! I'm having
                                  at               a RELIGIOUS EXPERIENCE
                               visi.com            right NOW!!
Reply to
Grant Edwards

Can't help in the non-internet realm but we've used the "Raven" from

formatting link
to send seismic data over cell networks. It has a serial port but you would have to provide a PPP and UDP/IP implementation in the PIC software, not trivial, but doable with the larger PIC's.

I'm not in the purchasing end of things so I have no idea what they cost, possibly a lot more than your budget.

Reply to
bob

Most GSM units will pass DTMF in the audio path.

100 byte == 200 nibbles == about 10 to 20 seconds. DTMF decoders can sometimes work in 'fast' mode where you do not need a silence gap if adjacent digits are different. If you have long strings of the same digit you can compress this using RLL.

--Rocky

Reply to
Rocky

Aw crap ...

"Unofficial" features can disappear at any time.

Latency may not be an issue, although it probably means I can't dial for data using a landline, only a similar cell phone attached to the pc where the data is to be stored.

Reply to
Luminoso

Are your sure Microsoft hasn't acquired the phone companies ? Sounds like their kind of evil.

Oh well, I suppose I can plug into the microphone input and create my own latency-proof 'modem' tones ... not THAT hard.

Whadda you think ... generate DTMF tones with the PIC and then use a DTMF decoder chip on the receiving end. ? Makes for a base-10 encoded data stream. Just can't change tones too quickly ...

Reply to
Luminoso

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.