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How to use AT command

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hossam abdo

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this is the circuit in the data sheet DTMF.jpg

but i change the 20pF capacitors to 22 PF, also i putted resistance 240kohm instead of 300k.
are these affect the function of the circuit?
thanks and need help please
 

alexxx

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hossam abdo said:
but i change the 20pF capacitors to 22 PF, also i putted resistance 240kohm instead of 300k.
are these affect the function of the circuit?
No put back the components provided by the datasheet. Try "playing" with the 100K resistance between pin 2 and the 0.1uF capacitor. Lower this value, in order to achieve greater amplification of the incoming signal. Try it until a few Kohms.
 

hossam abdo

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the same problem occurs when i use two mobile phones, but when i use one mobile phone with a land line phone , the operation achieved properly.
I do not know what is the problem?
 

alexxx

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the same problem occurs when i use two mobile phones, but when i use one mobile phone with a land line phone , the operation achieved properly.
I do not know what is the problem?

Did you try post's #23 suggestion? Are you using an oscilloscope to spot the problem?
 

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