Problem In DTMF robot

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Arnab Ray

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I have build the circuit for a DTMF bot using Atmega 16 and MT8870 DTMF decoder. I have checked the circuit and it is working perfectly when I connect the earphone jack from the circuit to the laptop and generate DTMF tones using a software for generating DTMF tones. But the problem occurred when instead of laptop, i connected the circuit to the earphone port of a cell phone. The circuit is not responding when i strike the keys of the cell phone..

Please suggest the solution to the problem, since the actual purpose of the DTMF bot is to drive it wirelessly through cell phone.

Thanx in advance..
 

get earphones plugged in to your cellphone and check does it really gives out dtmf tones.....
 



I must say I didnt catch the goal, this works over wire or over GSM network ?

You should post circuit.

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I need to clear this :

But the problem occurred when instead of laptop, i connected the circuit to the earphone port of a cell phone. The circuit is not responding when i strike the keys of the cell phone..
Click to expand...
 

@tpetar.....two cellphones are connected through calls on gsm nertwork and when u press any key on 1 cellphone, dtmf tones are heard on the other......this robot decodes those dtmf tones and moves the robot accordingly!

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arnab check your lead which takes the dtmf tones to mt8870....put a multimeter on its two ends---ground and left or right channel. Note that the multimeter is set to measure even the difference of 0.1v.
 

@tpetar: The robot works over the GSM network. Since the DTMF tones from the cell fone was not working, to test the circuit, I tried to simulate the DTMF tone through a software installed in the laptop and connected the circuit to the earfone port of the laptop..this method worked perfectly..but again when i connected the circuit to the GSM cellphone, the circuit is not detecting the DTMF tones generated by pressing the keys of the phone. I have attached the diagram of the circuit.




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@Alkeshwr: I tried out as suggested by you. The multimeter is giving a very low reading when i connected the circuit to the laptop..but the reading is zero when it is connected to the cell phone..do i need to add any amplifier circuit before giving the output of the phone to the DTMF decoder IC?
 

The headset option is activated. I am using samsung galaxy y with a 3.5mm earfone connector. Is it necessary to use old nokia handsets for DTMF robots?
 

How you connect handsfree with circuit input at C1, with wire or how ?

Try to decrease R1 value from 100K to 47K, sometimes I must lower to 10K for telephone devices.
 

@tpetar: yes, i have used wire to connect handsfree to circuit input..i am attaching a picture to show you the connection..

thanx again for helping out..


 

I tried out as suggested by you..I have replaced R1 (100K) with a resistor of 10K. But then also the problem is persisting. Will it be useful to introduce an amplifier circuit between the phone and the circuit?
 

Yes exactly. It works perfectly on PC output. But it is not working on cell phone output.
 

Did you try to hear DTMF codes generated by phone in handsfree in ears or to amplify phone out and connect to some speaker. Definitely problem is here.
 

put up ur earphones in the cellphone jack and check if it pumps out dtmf.....perhaps ur phone's jack is not working....
 

try after changing your gsm network,,,try on different networks
and operate on 2G mode.. may it work
 

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