DTMF encoder

[mytech]

Actually i wanted to know what type of tone would be available at pin 7. after constructed the circuit i gave tone o/p to input to the amp. but when i press the key it doesn't make any sense.. will it make sound if the circuit works?.. or let me know some ideas about that tone.. thanks..

 

[mytech]

Any possible ways?..

 

[Hero999]

You need to connect this circuit to an oscilloscope or a speaker to test it.

You could probably connect a high impedance piezo speaker to pin 7 or use an LM386 to drive an 8hm: speaker.

 

[mytech]

Yes i gave the o/p of 7 to Hi-Fi system Aux input.. but doesn't make any sound..
So it needs to amplify, then only it makes sound right.. will try with oscilloscope..

Also gonna transmit tone via rf, should i have to amplify before give input to transmitter?.. thanks for reply..

 

[Hero999]

Did you connect the 0V rail to the 0V side of the Hi-Fi's aux input?

I don't know what input your transmitter requires, you might even need an attenuator.

There are better ways of transmitting information over and RF link that DTMF.

 

[mytech]

yes sir i connected ground and 7th pin output to audio system say Left channel alone like mono input.. and then pressed the key.. i just tested encoder alone..

Here is my proj.

 

[blueroomelectronics]

You left out some important parts.
Add R1,R2,C1,C2 you might have more luck. Plus replace your zener you've probably killed it. And you probably don't need the zener if you're using 5V
Pin 7 is open collector, you've got to add a pullup. It's all in the datasheet.

 

[mytech]

Thanks sir, And i am using another separate transmitter not mentioned in the above circuit. so i need to generate dtmf tone alone. still i have some confusion
because data sheet contains lots more connection..

If i have dtmf generator circuit alone it would be much better to experience with.. thanks.

 

[blueroomelectronics]

Note, I was wrong it's an open emitter output. You'll need a pulldown resistor on pin 7 before the cap.

 

[mytech]

Ok sir, can you tell me the value of pulldown resistor..
Shall i follow the circuit mentioned above to generate tone?
A small doubt, i am generating dtmf tone alone , is that R2 & C1 belongs to dtmf circuit or fm circuit.. thanks

 

[blueroomelectronics]

Try 10K, and all you should need is C1 for starters (it will block DC which is good for your amp)

 

[mytech]

Thanks sir, got clear idea.
Will mesg. if any other problem exists.

 

[Hero999]

Plus replace your zener you've probably killed it.

I can't believe I didn't notice that.

 

[mytech]

Plus replace your zener you've probably killed it.

sorry for the inconvenience, what i have to replace.. what would happen if the zener connected like this?..

 

[blueroomelectronics]

Without a current limiting resistor from the 5V it may break.

 

[mytech]

Thanks.. still i didn't know this, thanks for good info.

 

[Super_voip]

This IC also does pulse dialing, check the MODE IN , Ithink it should be tied HIGH for dtmf