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.
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...........????
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
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???
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.