How to check if DTMF IC is working properly?

[joe1986]

how can i check if my DTMF IC is working properly or not...........any idea????

 

[nandhu015]

Re: DTMF CHECK

Simple

Connect it to a telephone line.
A epabx will also do


regards
Nandhu

 

[athelas]

Re: DTMF CHECK

how can i check if my DTMF IC is working properly or not...........any idea????

You need to feed it two sinewave frequencies, one from the lower group and one from the upper group of 4 frequencies simultaneously and verify the correct 4-bit result at the digital decoded output of the chip. Depending on the chip type, you may need to take the 2 dB +/- 1 dB signal level difference into account.

Good luck !

Hans

 

[joe1986]

Re: DTMF CHECK

hi nandhu015 .................do u have any diagram which shows how to connect it to the telephone???

 

[vietdung79]

DTMF CHECK

Which DTMF IC do you use?

You can connect it with a MT8888 to check if it transmit/receive right or wrong.

 

[joe1986]

Re: DTMF CHECK

the IC IS DTMF 8870..................ITS ACTING AS A DECODER

 

[laktronics]

Re: DTMF CHECK

Hi,
Have alook at this site : https://www.electronicsforu.com/EFYLinux/circuit/jun2003/CI-2-DTMF.pdf .
What ever numbers you dial from the phone, should show up on the LEDs.
Regards,
Laktronics

 

[joe1986]

Re: DTMF CHECK

THANK a lot doctor laktronics........................DO U HAVE THE MAY 07 edition of EFY..........there's a file called "WIRELESS TEXT MESSAGING OVER MOBILE/LANDLINE...........????

 

[segmex]

DTMF CHECK

use oscope to view the dtmf signal ..

 

[laktronics]

Re: DTMF CHECK

Hi,
I just remebered, your 5V supply should not have a safety earth connection, since telephone line is already earthed through +ve of the battery. I don't have the May Issue, you may get it from their site?
Regards,
Laktronics

 

[joe1986]

Re: DTMF CHECK

hi .....doctor laktronics there is one problem ...........the site is asking for username and password of subscribers..............actually i subscribe for ELEKTOR ELECTRONICS...........and not EFY ...................are you a subscriber???

 

[vietdung79]

Re: DTMF CHECK

the IC IS DTMF 8870..................ITS ACTING AS A DECODER

Have you made a test board?
If you have, it's so easy.

Connect your phone line to the input of 8870. Call from other phone. Hook up the phone which connect with 8870. Then press some numbers from the caller phone. If your test board can receive what you press , it's working well. That's all.

Regards.

 

[joe1986]

Re: DTMF CHECK

whts a TEST BOARD AND HOW TO MAKE IT???