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

Ah ... I had just proposed using DTMF tones to someone further up the thread. Don't even have to have a GSM phone, it will go over the regular audio. Keep the speed low enough and there shouldn't be any problems with network latency. Four or five base-10 "bits" per second would serve MY needs.

Reply to
Luminoso
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Worst case they turn it off and you have to pay for data service.

No, it works fine with normal landline modems (at least dialing from mobile to landline works fine).

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Reply to
Grant Edwards

BTW, there's another "column" of DTMF tones (usually referred to as A B C and D) for a total of 16. Consumer phones never had that extra column of buttons, but some of the telco equipment I used to work with did. That means you can transmit a nibble at a time.

The Clare 8880 seems to be a popular transceiver (never used that one myself).

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Grant Edwards

If you don't need much inter-activity, I suggest you forget about a modem and use SMS instead. There are plenty of low cost sytems doing that. Google for PIC SMS PHONE.

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Cheers

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Manfred
Reply to
Manfred Bartz

Did you notice that none of these links are in the USA.

Cell phones in the USA can not SMS from an external device.

Another gotcha !!

Good Luck

donald

Reply to
Donald

I came across a $41 DTMF -> RS232 unit from

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that will also translate the extra tones. The actual tones ought to be pretty easy to make with a PIC, might try using the PCM outputs with a little filter to round off the edges of the squarewaves.

Oddly, dschmidt doesn't have a 232 -> DTMF translator. Does have some neat-o multi- channel and relay stuff however. Future ideas ...

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does have such a thing, albeit for $129

Motron makes a 2-way board for $129 ('sale' $99) http://209.51.151.50/ASCIItoDTMF.html It would take some of the load off the PIC, but does add an extra component and 25ma of power draw while it's on. Might be the easiest way however for 2-way data exchange between field and base station. If I decide I don't need the field unit to hear anything, just send data when the phone rings, I could still synthesize the tones with the PIC.

Oh yea, gotta get a time chip that can send a wake-up signal to the PIC ... low-dropout voltage regulator, or would a tiny switched supply be more economical, zener&resistor for simplicity ... details, details ....... :-)

Anyway, seems that anytime you hear about someone wanting to do remote data-collection they're always talking a little web-server, tcp/ip and a high-speed connection. Fine if you've got a hidden camera at a nude beach or something ... but a lot of real-world data can be condensed into just a handful of bytes and a super-LOW-speed connection may be the most economical approach by far. Turn that $2000 weather station into a $500 station with a really low phone bill.

Reply to
Luminoso

years ago i had this odd idea about transmitting data by counting the number of times a phone rings. eg: 1 to 3 rings = 0, 4 to 6 rings = 1,

7 rings = end of data.

your remote device would need to be able to listen for rings on the phone's audio when it was placing a call, and would obviously need to be able to detect the ring on an incoming call. these don't sound too hard/expensive to do.

this would be a terribly slow way to send data. and you'd need a pretty good ecc scheme. but it would be free till the phone companies figured out what you were up to. they might never, if you had random delays between bits. say your thruput averages about 1 minute per bit, that's about 180 bytes per day. plenty fast for sending the temperature every hour from a remote weather station.

there are several companies that let you setup a prepaid cell phone for around $100 per year. once you pay for the service, sending the data wouldn't cost you a thing since telcos don't charge for unanswered calls.

the reason to have a range of rings to represent each binary value is that when you call a phone there isn't always a one to one correspondence between the ring you hear in your handset and the ringing the person at the other end of the call hears.

mark

Reply to
mhahn

... snip ...

That's because it is so simple. One way is to switch a dual LM555 between two frequencies (although you may have to worry about the frequency stability). You don't need much low pass filtering since the phone system itself is a band-pass. Another is two build the appropriate frequency dividers and have the serial signal select between two choices in each of the high and low bands. The original bell implementation did it all with one transistor and a tapped transformer.

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Reply to
CBFalconer

That sounds interesting -- is there any publically available documentation on that?

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Reply to
Grant Edwards

I'm sure there is, but I don't know where. The other methods would be easier today, you don't have access to a cheap custom wound transformer. You might be able to pick up an older phone built by Western something (AT&Ts manufacturing arm in those days) and emasculate it. It will be driven by a 4 x 4 contact matrix.

I suspect dmr (dmritchie, of k&r) would know. He occasionally posts in comp.lang.c and alt.folklor.computers.

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Reply to
CBFalconer

[...]

I'm sure. It was jut idle curiosity.

Wester Electric

The only genuine Weco phones I've got are rotary dial.

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Reply to
Grant Edwards

This is a clever idea ... and it takes advantage of the phone companies, which doesn't hurt my feelings very much.

So long as you didn't need to xmit a lot of data - just a temperature and/or rainfall and/or humidity or whatever - it might indeed be adequate.

I started this thread looking for cheap cell data service for distant environmental data recorders. Looks as if there is no such thing, not exactly anyhow. Instead, I've decided to "cheat" by using DTMF ... you know, the sounds the touchtone buttons make.

I found a company that sells a bi-directional DTMF -> RS232 / RS232 -> DTMF boards for $99 which send at five to 40 tones-per-second (speed depends on the local system of course). I can easily encode my meager data in 10 to 16 bit 'bytes' and, by just using the mic/earphone jacks attached to the board, pay only normal 'voice' rates for the cell connection.

Using phones on minutes-only plans, I can probably get away with ten or twenty *CENTS* per day. A regular voice account will rip you off for thirty or fourty dollars a month, adding data capability jumps that up even more.

So, while everyone else concentrates on expensive web servers accessed over expensive data-grade cell connections, those of us who don't need to xmit much data really ought to look into using DTMF. Bi-directional might not even be needed for some applications, though it does simplify a number of things ... like 're-transmit, there was a checksum error".

Now I've got to find some cheap phones that put a signal on their buss when they get an incoming call, or can be turned on by powering a pin when the 'brain' of the environmental station tells it to. I suppose I could always use the ring noise or vibration to turn on the other stuff ...

Reply to
Luminoso

The 'princess' phone may be of about the right vintage -- push button. At the time, if I recall, they used 4-wires with the other 'pair' for power to light the phone. A practice, I think, they quickly learned to cease. (I believe I may still have a few "princess" phones around here, somewhere, picked up as free surplus around 1972 or so.)

Jon

Reply to
Jonathan Kirwan

Ahhh -- I didn't realise that.

However, if one is determined enough, one could hook into the phone's keypad and pretend to be a human pressing keys... ;-)

Cheers

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Manfred
Reply to
Manfred Bartz

Wow! That'll be some cell phone!!

;-)

Reply to
Manfred Bartz

I am talking about POTS :-) Who reads subject lines?

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Chuck F (cbfalconer at maineline dot net)
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Reply to
CBFalconer

I can testify to that: it hurts.

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Grant Edwards

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