dtmf project help !!!

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mihir08

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i am using the following ciruit to decode dtmf tone. i am not getting any output .
is there any mistake in circuit . i have tried it several times but no results !!
are any additional components recquired . actualy i am trying ro make a dtmf controlled robot.

if any one has some useful links plzzz do post !!
 

Hi,

It is a Analog type Encoder/Decoder. I think your Micro not recognizing directly from 8870. What Micro you are using ????

Sudan
 

Hi all
There is no fault in your drawing
some advices
check the xtal
and connect leds to the outputs with 330 ohm resistors serial
 

as technodict said i am not using any mc . i am planning to connect Q1 Q2 ,Q3,Q4 directly to L293d
motor driver.
 

mihir08 said:
as technodict said i am not using any mc . i am planning to connect Q1 Q2 ,Q3,Q4 directly to L293d
motor driver.
Click to expand...

Then You must use pull down resistors at lets say more or less 10 to 47 Kohms.
 

dear i have recently used 8870 and want to help you
first tell me from where you are giving input to 8870
then i'll tell u more
 

hi tauqeer , thanks for showing concern .
i am giving the i/p from my pc using a dtmf generator software.
i also called from a cellphone and pressed all the keys several times ... but no result
 

can u post a better and working schematic of a cell phone and cm8870 interface without using an MCU?actually i ma looking forward to drive relays with cm8870 dtmf decoder.
 

@technodict
if you want to drive relay , u can simply add trasistor drving ckt with q1,Q2,.. as input to those trasistor . if u want relay one to be active press one(0001)
for relay two - 2(0010), for relay 1 and two on simultaneously 3(0011) and so on .

though it may not be as convienient as it would have been with muc . using a simple pic 16f84 circuit ,you can make it much simpler to use .
 

i think there is a problem with your DTMF generator so
try it with the nokia 1200 cell phone by connecting head phone to it. Turn on the keypad tone of your 1200 cell phone before testing and properly connect the head phone wires with your circuit if problem also exist then interchange these connection and then reply me back
 

i already did this with nokia 1100 . what one of my friend said is that - dtmf signals are not produced unless the call is in progress . is it so ?

do i need pull up resisitors at the o/p .
i am connecting led directly between Q1, Q2 ... and ground .
 

now tel me the input capacitor you have used with 100k resistor at the input it must be 0.1uf capacitor(104)
 

I've been working on something similar with CM8870, and needed to replace the 100K between input and pin 2 with 1K + 50K pot and finetune it every time I connected it to something else generating dtmf tones.

(And I also had the 104 capacitor at the input)
 

Changing the 100K is not related to the detection of frequency. But if it then works after modifications, its good. But it should be noted that changing the same to lower resisitances may damage the chip while the telephone line supply 50-70 volts AC while ringing. Cheers
 

There is slight revision in ur hardware..
Try this things out.. use one splitter or take parallel lines from ur existing landline fone..
attach green wire of ur fone to IN+ directly & red wire to ur current input pin(Tone input from fone)
after that call on ur landline from anywherr then after ringing pickup ur landline fone and keep in that offhook position only
now press any key from ur landline or from where ur calling it then Q1-Q4 will show you respective BCD pattern for pressed key you can check it with connecting LED through ULN2003 to Q1-Q4..
try out this...
If it doesnt work buzz me, i have tried this 3 year ago, that circuit is still working...
 

I have too worked with the said schematic without any problems. Only thing in my project i found troublesome is to swicth on and off and appliance, we need to press 1 which turns on the device. To switch off the same, immedialtely, within 2-3 seconds, we need to press * and then 1 agin. But it is working fine till date...
 

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