8870 DTMF decoder Problem!

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UroBoros

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8870 dtmf decoder

Hai

I am using 8870to decode a DTMF tone from a telephone line.


But the decoder always out a different value.

for 2 it outs 3
for 4 it outs 5


That means the LSB of the data line always come as 1.

I checked the line for any short or anything like that.

Any idea?

Anything to do with gain of 8870 that it outs error values?

I tries 270k and 470k as feed back resistor.No change?

suggessions please

picstudent
 

8870 dtmf

HI HAVE WORKED ON THIS DTMF DECODER LONG BACK.DIDNOT GET ANY SUCH ERROR EVER. BUT I REMEMBER THERE IS A PIN IN THIS CHI WHICH BECOMES HIGH WHEN EVER ANY DTMF SIGNAL OF ANY VALUE IS RECEIVED. I THINK U MUST BE TAKINHG IT AS UR LOWEST BIT. CHECK THE PIN DETAILS.

IF U STILL DONT GET LET ME KNOW
I WILL FIND OUT
 

    UroBoros

    Points: 2
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dtmf 8870

Can you show us the schematic?

ps. What did you use for Ringing, Hook up etc. from the line?
 

    UroBoros

    Points: 2
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decoder 8870

Hai

Schematic is not in softcopy now.Only in paper.

Now no ring detection is wired.

I have just connected the Delayed steering output pin (of 8870)to a input pin of MCU and polls it for a signal.

When that pin shows a high I am enabling the out enable pin of 8870 and reads the port.

regarding the DTMF 8870 schematic , it is the one showed in their datasheet.

thanks
picstudent
 

holtek 8870

Check if you have left any unused pins floating
 

    UroBoros

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pins of dtmf decoder 8870

Hai

Thanks all.


The DTMF decoder CA8870 was faulty.replaced it and all ok.

Actually I didint suspect such a possibilty.

That chip was 3 years "old" in my junk box. It was working then .(3 years before).

Thanks to all

picstudent
 

ht9170 bug

DTMF DECODER ... safe and low cost ( verified ) from HOLTEK HT9170
 

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