Telephone schematics..

[mytech]

Hi i am doing DTMF project, i hav few old working Telephone sets.. i know it has both dtmf encoder & decoder.. without telephone lines i need to generate dtmf tones by giving external supplies , how its possible
Thanks

 

[Gayan Soyza]

Look into the DTMF generator IC inside your tel & give supply according to the datasheet.

 

[mvs sarma]

Hi i am doing DTMF project, i hav few old working Telephone sets.. i know it has both dtmf encoder & decoder.. without telephone lines i need to generate dtmf tones by giving external supplies , how its possible
Thanks

Wire up as indicated below.The current flowing in the telephone should be around 20 to 35 mA

after the 1K resistor place a 10uF capacitor to the other limb of supply. this I forgot before posting the schematic

 

[Gayan Soyza]

Oops I have misread OPs thread I thought He's going to power up the built in DTMF generator seperately.

 

[mytech]

Thanks this is what i needed.. il try this.

 

[Raz00]

I have a problem interfacing my TP5088 dtmf generator and pic 16f84a to the telephone line as the audio transformer isnt available where i live so can i use anything else other than the transformer?????????????????

 

[audioguru]

RAZ,
This is your third thread about your simple problem that I answered in one of your other threads.
Steal a transformer from an old telephone product or buy a new one from a large electronics parts distributor like Digikey.

 

[Raz00]

yeah but i just mentioned that i cant find it in any telephone nor buy it as it isnt available in any electronics distributor in my city PLUS i noticed that modern integrated telephones dont use audio xfmr so i thought there must be a substitute for that xfmr !

 

[mvs sarma]

try to purchase 1:1:1 pulse transformer. these are sold in market. they might work upto 5KHz

My city--- joke .
How do we know where you are?
see across names of Audioguru and mvs sarma clearly mention where we are !!
however check for part no RS Stock No.210-6324 of RS Components UK

 

[Raz00]

Hey i managed to get the xfmr from an old telephone but its not 600 ohm its 200 : 160 and with centertaps . I found an interface ct. connecting 470 ohm along with the xfmr and the telephone that solved the power problem i had but the call still cant b place .The telephone line doesnt seem to recognize the generated tone and keeps giving me that tone that is waiting for you to dial :s:s what could b the problem ????

 

[audioguru]

Touch tones (DTMF) must be at the correct level on the telephone line.
Maybe your telephone line is set for dial pulses instead of for touch tones?