I'm building this project a part of which will entail sending DTMF tone over an RFS radio to a recieving radio.

Transmitting the DTMF tone is done by a PIC16F628, which I happen to be programming with the PICBasic Pro Compiler (Yes I know basic is bad :wink: And No, I did not shell out $250 for the compiler). Fortunately DTMF out is a standard function in the PICbasic compilers so I have no problem there.

The trouble comes in when I want to recieve the DTMF tones over the second radio with another PIC16F628. I don't know how I could recieve the code using the PIC directly. So I thought that maybe I could use an external IC. Unfortunately the only one I can find is from Parallax.com and they overcharge for everything (I much prefer mouser.com or Jameco.com). So I wonder if any of you know were I can get one? I've scoured google without a single hit. (But I keep hearing people talk about them.)

If you don't know of a place I could find a DTMF decoder, but know of a better way to recieve the DTMF tones, or a better way of sending data over a radio please tell me.

Micah

 

DTMF decoders have been around for years , National Semiconductor might still sell it..dont know for sure ..
did you try google ?

 

What are you actually trying to do?, if it's actually sending 'data' over a radio link, then DTMF is probably the worst way of doing it you could chose!.

If you're using licence free radio modules, they are designed for sending data directly, although you need to implement a suitable coding scheme (such as Manchester coding) - you can buy modules that already have this built in!, these work as a simple serial link over radio.

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Yes I have tried searching Google (Google is THE best search engine), but maybe I need to try again....


Nigel,

I'm not actually sending 'data' I'm really sending commands. This project is based on budget :-D So I am making the radio link as cheaply as I know how.

I'm using license free FRS (Family Radio Service) radios which typically a 2 mile line-of-site range. These radios are NOT made for sending data. They are made for voice communications (They are 400 Mhz FM transievers). Thats why I chose DTMF. (BTW, ham operators have had rather good success using DTMF to transmit actual data )

I'm using them because I can get them off ebay cheaply, and because radios made specifically for communicating between things such as microcontrollers are expensive (especially when they reach the 2 mile range...)

So all that is going to happen is:

Microcontroller A will send a code (lets say DTMF 1) through Radio A. Radio B will recieve this code and send it to microcontroller B which will "hear" it and act accordingly.

Really simple and I figured DTMF would do the job nicely.

Oh, and this remote controll is for a jet powered boat my older brother and I are building. If you know of any better/cheaper way of doing this please tell me.

Thanks!

 

You can use MT8888 which is a DTMF transceiver.

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sounds to me like it will work..

 

It's still probably the worst possible method you could choose, and certainly NOT the cheapest!.

On the 'worst' side, you have hardly any control at all, just crude (and slow) ON and OFF.

Far easier (and cheaper) to use the microcontrollers with 'modems', the transmit side can generate HIGH and LOW tones directly (or you could use a 555 or similar). On the receiver side you can use an NE567 as a tone decoder, to recover the serial data.

This would allow you to send any data you want, and include 'analogue' values for steering etc. It's a very old and tested technique.

Another method would be to transmit bursts of audio (with the pulse width representing the servo position), use an NE567 to recover the data again, and you have standard servo type pulses over an audio link.

Incidently, why not just use a standard radio control system?.

__________________
PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk

 

I agree with nigel... I would never trust a jet-powered boat to such an extremely crude control system!

if you're steering the boat with simple DTMF tones, I have a feeling your boat will end up at the bottom of a lake quite soon :lol: there's such a thing as digital proportional steering for a reason!

even a simple regular serial link over radio would be far better... and serial isn't that hard to do on a PIC (I imagine that your PIC compiler probably has routines for that as well)

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Hi, I am trying to something similar, I work in a school and the students always mess with the clocks on the classrooms, so I figure it out that a series of digital clockes controled by a pc would make the trick. As a bonus I would like to be able to deliver audio messages to the clocks and they could work as speakers also. I imagined that a cheap fm transmitter, some radio receivers, pics, leds, etc. would do it. But the only way I saw to transmit the time was DTMF, could you elaborate on other alternatives? thanks

 

Google for FSK. It is a common method for transmitting data over an RF link.

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I used MT8870 and two PIC ics for creating RF remote control and it works great. I got MT8870 DTMF from electronics-diy.com some time ago. I just checked the site and they still sell it. Here's the link http://electronics-diy.com/store.php...remote_control