Wireless Intercom system

[Edigate]

Hello All,
I've been asked to build a wireless intercom system.
I need ideas on how to go about it.
gods, oracles, experts, where are you? :!:

 

[audioguru]

You didn't post any details so maybe just a pair of kids' walkie-talkies will do.

Maybe you want each one to have a press-to-talk button that turns-off its receiver and activates its transmitter when transmitting.

Maybe you want "full-duplex" so that both people can talk and be heard simultaneously. Then one unit needs a frequency to transmit on while the other unit receives that frequency and another frequency for the other unit to transmit on. Then you will have long-distance acoustical feedback howling and need to add a "voice-switching" (Motorola and ON Semi have a couple of good speakerphone IC's for it) or DSP cancellation circuit to each one to mute its microphone when receiving. :lol:

 

[Edigate]

It is a full duplex system. It is not necessarily for two persons alone but for up to ten persons. I'll appreciate some good websites.
Thanks.

 

[audioguru]

What about dialing the other transceivers individually like intercom systems do? Then each intercom transceiver will need a different pair of RF frequencies. Each transceiver will need a keypad dial so it can transmit and receive on the correct frequencies. Use a separate button to transmit all-call.

Intercom systems use a special arrangement for replies to all-call. If the other 9 transceivers were full-duplex during an all-call then they will hear background sounds and noise from the other 9 transceivers and communication will be impossible. All-call is usually transmitted only by the originator then a single person replying calls him back.

There are probably many more details that you didn't think about. :lol:

 

[Electrix]

Check out the LM380 application note. They are one of the easiest to build, but would require a lot of modifications. For eg: a keypad switch interfaced to a MCU, which has a look up table to determine which pair of transm-receiv to be set ON.
The MCU here acts as a controllable switch

 

[Edigate]

I think I need to start from scratch. I need to do an indepth study of wired intercom systems before going into the wireless stuff. I have 6 months to submit this project, so I can learn everything from the basics.
All I need now is sites where I can get good materials.
Thanks for the support.

I'm coming up.

 

[JimB]

Wireless infers the use of radio, this has regulatory and type approval issues associated with it.

If you want full duplex, you will need to use two frequencies with suitable spacing so that the transmitter does not desensitize the receiver.
Using two frequencies is no good if you want full duplex between several stations at the same time.

What range (distance) are you looking for?

If you want to implement a "conference" call, you will have a problem with more than on transmitter being on at the same time. The speakerphone ICs mentioned by audioguru may help here.

Good project, get your thinking cap on!

JimB

 

[Edigate]

Hello,
The wireless system in question is for a range of 1km. I'm still waiting for site references!!!

 

[Nigel Goodwin]

Hello,
The wireless system in question is for a range of 1km. I'm still waiting for site references!!!

I don't think it's something you're going to find sites about?, it's really quite complex and encumbered by licencing restrictions.

 

[i_build_stuff]

You can get unlicensed transmitters in the 2.4GHz range to talk pretty far; 1km should not be a problem unless it's got to go through buildings. The FCC rules for these frequencies require spread-spectrum, which makes things more complicated, but you can get the whole transceiver on one little chip or module anyway. Most of these have digital inputs / outputs, so you can send commands along with the audio stream (these commands can include a list of intercoms that will respond to your signal).

 

[JimB]

The FCC rules for these frequencies .....

But what if he is not within the juridiction of the FCC?
There is a lot more to the world than the USA.

JimB

 

[i_build_stuff]

But what if he is not within the juridiction of the FCC?
There is a lot more to the world than the USA.

JimB

Sorry if that came across as ethnocentric . It really wasn't intentional.

Perhaps the OP can tell us where he is posting from, so that someone can provide info relevant to that location?

 

[Nigel Goodwin]

Perhaps the OP can tell us where he is posting from, so that someone can provide info relevant to that location?

Perhaps you might consider filling your location in as well?, there are many questions (like this one) where it's VERY relevent!.

 

[i_build_stuff]

Perhaps you might consider filling your location in as well?, there are many questions (like this one) where it's VERY relevent!.

done

 

[Edigate]

Hello,
I'm in a part of the world where communications systems regulations are quite relaxed. Guys like us willing to know how to work with wireless equipments are somehow encouraged.
What I need right now is info on how to go about my project.