Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

GPRS/GSM Modem info needed.

Status
Not open for further replies.

cobra1

New Member
Ok, so just an idea i had, but not at all sure if it will work or even if it can be done.

Imagine having 1 GSM modem based in a building that passes information it receives to a radio module and broadcasts it to any listening devices in that building.
Now im out and about somewhere and i call that modem from a tablet PC.
Is it possible to establish a link whereby i can then send data to that modem and the information sent be broadcast via radio, then the radio will receive a response and send it back via gsm modem to my tablet so i can read it.

Can this be done?
If anyone knows it can what do i look for for information on the subject, iv google various keywords but not getting the correct answers.
 

simonbramble

Active Member
this would take some developing, but is best done with modules. For the GSM module, look at companies like Telit. For the local 'radio' comms, look at someone like Jennic (now NXP). The interface between the 2 will be the hard bit (but by no means impossible). You could also look at Bluetooth modules too.
 

Diver300

Well-Known Member
Most Helpful Member
It is possible. You need to separate the tasks, and the protocols will be different, so you need a microcontroller or similar to talk to the GSM module and the radio module.

There are three ways that I know of to communicate through a GSM modem.
1) By text message. This is the simplest, but potentially the most expensive. You can easily send a text to the GSM modem
2) GPRS internet connection. This needs some server that the GSM modem will connect to, although that could be just an email account. The problem with that method is that the GSM modem needs to initiate communication. That might be just checking for new emails, or asking again for a web page to see if anything has changed.
3) GPRS persistant connection. https://en.wikipedia.org/wiki/Persistent_connection I don't have any direct experience of that, but a persistant connection allows the GSM modem to open a connection to a server, and then the server can send data at any time. That needs the server to be configured to use that connection.

Whatever you use, your microcontroller will receive the information and then send it out by radio. With radio modules, they are point-to-point communication and although you need to decide on a protocol, as long as the receivers are turned on, they can receive information.

The return journey is the reverse, but of course the GSM module can send the data to a server, possibly by email, and there is no problem worrying about leaving connections open.
 

cobra1

New Member
thanks for the responses. i currently have the radio side of things sorted. it will be the link between the two gsm modems that i will need some guidance with.

a permanent connection is not required. whatever is easiest.
 

Diver300

Well-Known Member
Most Helpful Member
It might also be possible to just make a data call directly between the two modems. However, I have no idea how that is done. Also, I don't know what is possible with a tablet PC. I always feel that it is easiest to stick to a web-based interface if you have a PC, as it removes the need to run code on the PC.

How often do you need to communicate with the remote site? How much data goes each way?
 

cobra1

New Member
The remote site will be in near constant communication, the end devices will be constantly updating there data to the tablet, if the tablet is off then data communication will stop. Its only when the tablet is connected that data is transfered.

The reason for using a gsm modem is simply so i dont have to rely on an internet connection, if i can get a mobile phone signal then im pretty much sorted.

Data transfer is likely to be something like 100bytes per minute
 

Diver300

Well-Known Member
Most Helpful Member
As I see it, the problem is telling the GSM modem when the tablet is on and therefore when data is to be sent.

You could text or call the GSM modem to tell it to start sending data. Alternatively, it could check with the server every few minutes. It depends how quickly you want it to start working when you turn on the tablet, and how much data is going to cost.
 

cobra1

New Member
Basically my devices receive commands in ascii format "GETTEMP", "SETTIME" that sort of thing. They then reply in ascii giving details of temperature, humidity etc.

Locally this isnt a problem and i am able to control the devices from hyperterminal on the PC. What i need to do is extend the range a little so instead of having to control it all from a PC in the same building i can control it from anywhere.

A direct link between the GSM module and the tablet would be of most benefit as it would remove servers etc from the equasion.


So i call the gsm module, transfer data "GETTEMP", get response, "86", hang up.
I now have a temperature of 86 on my tablet.

Can this be done as simply as this?

I looked into the texting method and your right, before you know it, it gets very expensive.
 

Diver300

Well-Known Member
Most Helpful Member
You might be able to get the tablet to call the GSM modem, and then transfer data. You would need the GSM modem to answer the call and set up a data connection. I don't know how that is done, but it might be explained in the Telit datasheets. If you don't mind paying for a call each time you want data, that would work.
 
Status
Not open for further replies.

Latest threads

EE World Online Articles

Loading
Top