problem with DTMF project

[garyx]

I am new to electronics and learning as I go. My project is a DTMF receiver working off a cell phone and activating a series of relays. The integrated circuit that was called for was a CM8870, which was not available and was substituted by the NTE 1690. An ear piece connected to the cell phone and the wires to the ear plugs were cut to allow one wire as input to the IC and the other for ground. After dialing and then pressing a number on the phone nothing happens. There is no current from the phone to the IC. As I said I don't know much about this, can anyone give me a hand?
thanks

 

[audioguru]

The CM8870 was an old DTMF receiver.
The NTE1690 is a DTMF dialer that is used in a telephone. It is not a receiver.
Here is its datasheet: **broken link removed**

If you can't buy an old DTMF receiver iC then maybe there is a kit available with one.

 

[Gayan Soyza]

I have checked DTMF external decoding circuit is working well with land lines but not with mobile phones.

When the DTMF decoder connected to the home land phone & when you dial & press some numbers from another land phone its working.

But to the same circuit (Land phone + decoder) if you dial from a mobile phone its not working well.If the circuit in the vicinity then its ok.But if you are in some other area problem.

In your case ear peice is placing near cellphone speaker loosing too much frequency strength.Something to consider.

I waiting to see your final progress.

 

[petrv]

I don't know CM8870 but I guess it is a clone of Mitel/Zarlink MT8870 which is a well known chip - try that one.

 

[aljamri]

I have checked DTMF external decoding circuit is working well with land lines but not with mobile phones.

I've used it with both and it work well. Thats in Vellman DTMF ket.

In your case ear peice is placing near cellphone speaker loosing too much frequency strength.Something to consider.

No, he well cut the ear peice and connect its wires into his circuit.

I waiting to see your final progress.

me too.

 

[aljamri]

I don't know CM8870 but I guess it is a clone of Mitel/Zarlink MT8870 which is a well known chip - try that one.

Yes, you can get it from Futurlec.com with less than $2 (+PP). At this link:

https://futurlec.com/cgi-bin/search/search.cgi

and attached is the datasheet.

 

[garyx]

thanks for the help. I ordered the new chip from Futurlec, and will continue on when I get it.