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dtmf decoder mt8870 with microcontroller

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foxbrain

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is there a circuit i can add to the mt8870 to connect it to the microcontroller and what it do?
i made a circuit as on mt8870 datasheet a on the dtmf input i connected it to a telephone and on the q1-q4 to leds but when i dial any number on the phone no led turns on !!! so what's the problem?
 

tpetar

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Try circuit what i send you.

Datasheet circuit not completed with all parts, maybe you make some mistakes.

Try to decrease value of R1 between 10K and 100K.


See another example. Its PSTN remote control with codes (switch On/Off and sense switch) :

shema.png

Pay attention how IC is implemented.
 

tpetar

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Check all connections. You can decrease more R1 try 22K.

What capacitor you use for C1 and C2 ? What type ? Should be block capacitor!
 

foxbrain

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same result in 22k
i'm using non polar capacitor and they r 100nF
 

tpetar

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Did you connect on telephone lines ?
Phone are DT (dial tone) not pulse dialing ?

Did you check gnd connection between one telephone line wire and pins 6,9 and R8 ?

Try to replace C1 and C2 ? What voltage value for C1 and C2 you used ?

Check pin 1 and pin 2 !


Did you make all exact as circuit diagram in project ?
(this must work I try this!)

Check all you miss something! Check all value of parts!
 
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foxbrain

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i connected it to the phone line and to a telephone and yes i'm using DT
i checked the gnd it ok....
i think i have to make the u told me nothing else can be done.
 

tpetar

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For R7 put 100K

Did you check +5V on IC ?


Another example :

dtmfdecoder_schematic.gif


Try to put pin 5 to gnd as 6,9.

On pin 18 and 10 you should have +5V.


My friend this should work 100%. You make somewhere some mistake.
Take some break, and later back to project, or tomorrow. New look and new ideas will show up.
 
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foxbrain

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woow!! it looks we misunderstand each other i'm talking on the one that is on the datasheet and u r talking about the project :roll:
anyway i'll do yr project as i meant in #5 as soon as i have the elements of the circuit in these days...
 

foxbrain

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Sahu yr circuit is cool but i don't need a big one (complicated) , i need a simple one without microcontrollers for now
tpetar i made the one u gave me in 2# and the one on 6# is the same but it didn't work either... i checked the voltage the lines.... nothing is wrong but i noticed that the voltage of the line before i connect the circuit is 63v but when i connect the circuit it turns 0.7v so does that make sense? is there another solution?
thanks
 

foxbrain

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it finally worked the error was that i tried this circuit on the line that has the adsl with contains an adsl filter so it didn't wrong correctly but when i tried it on the line that doesn't contain the filter it worked.... do u know how can i solve it???
 

tpetar

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it finally worked the error was that i tried this circuit on the line that has the adsl with contains an adsl filter so it didn't wrong correctly but when i tried it on the line that doesn't contain the filter it worked.... do u know how can i solve it???

ADSL filter goes first, after goes all othere phone device including this device !!! ADSL filter have one jack for phone and one for line, buy some deviders and put multiple phone devices. :wink:
 

ramza038

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Brothers,i need to make a project "device control using dtmf" . I take the dtmf signal from mobile phone head set. Plz help me.
 

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