DTMF IC Test_failure

Thread Starter

vinodquilon

Joined Dec 24, 2009
234
Pls find the attachment.
After setting the circuit (using mt8870) , when I switch on the circuit LEDs 1,2,3, & 4 are all suddenly ON without detecting ring volt and key press. Does this mean the IC is out-of-work. I have only one IC, otherwise I would have gone for IC replacement.​
 

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bertus

Joined Apr 5, 2008
22,270
Hello,

What is the audio level of the dtmf tones?
The datasheet claims it must be round -25dBm.
See the datasheet for more details.

Greetings,
Bertus
 

Attachments

Thread Starter

vinodquilon

Joined Dec 24, 2009
234
Hello,

What is the audio level of the dtmf tones?
The datasheet claims it must be round -25dBm.
See the datasheet for more details.

Greetings,
Bertus
But the audio level is determined by the phone from which we generate key tones, I think all over the world it follows a typical level value and it can be easily identified by the DTMF decoder.
 

bertus

Joined Apr 5, 2008
22,270
Hello,

Is the circuit connected to the phone line?
The phone itself get the power from this line.
Without connecting the circuit to the phone line no dtmf tones can be generatted.

Greetings,
Bertus
 

Thread Starter

vinodquilon

Joined Dec 24, 2009
234
Hello,

Is the circuit connected to the phone line?
The phone itself get the power from this line.
Without connecting the circuit to the phone line no dtmf tones can be generatted.

Greetings,
Bertus
Telephone line directly connect to the circuit and a parallel local telephone connection is also taken as in figure.
 

Thread Starter

vinodquilon

Joined Dec 24, 2009
234
Pls find the attachment.
After setting the circuit (using mt8870) , when I switch on the circuit LEDs 1,2,3, & 4 are all suddenly ON without detecting ring volt and key press. Does this mean the IC is out-of-work. I have only one IC, otherwise I would have gone for IC replacement.​
well done!!!!!!!
Ya, I have replaced with another vendors' IC (MT8870CE). Now it is working fine.But on

power-up all states are HIGH, then on pressing keys it obeys the actual Truth table. I think

it wouldn't be a bottleneck for my project as I feed the DTMF IC outputs to a decoder. I can

utilize the decoder outs in any way as I desired.
Thanks for all support by
Siong Boon
http://www.siongboon.com/projects/2005-07-18_dtmf_circuits/
 
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