DTMF and PIC 16F628A

[ultramegaok]

Hi
I'm really new with DTMF staff and I have been trying to dial a number throught the telephone line, I had tried differents circuits but not one has work succesfully, with the one attached sometimes I have a response from the central but not able to complete the call never.... I'm using PBP with a 16F628A PIC @ 4MHz. any help what am I doing wrong??? Somebody has completed successfully this project with those components???. Is the pic able to give a clear DTMF tone or I have to implement something else besides what the PBP manual shows??

[BobK]

Hello ultramegaok,

Start by going to http://www.epanorama.net/circuits/te....html#audioint. This will be your wealth of knowledge on telephone line interfaces. I can guarantee that your circuit will NOT work. You have to be extremely careful on what you put on the telephone network. I only glanced through this site but I saw a very basic interface circuit that you should be able to construct without too much difficultly.

You can find several PBP telephone line programs at www.melabs.com. Look under sample programs and you will find a program that lets your PIC dial in pulse and DTMF.

I am going away for a few days so I'll check back in Tuesday night. Start reading and have some fun!!

HTH,

BobK

[ultramegaok]

tried this circuit which didn't work too...

[BobK]

Hello, ultramegaok

You will not be able to send any thing out to the phone line through a bridge rectifier!
The only thing the bridge rectifier is good for, on a phone line, is drawing power FROM the phone line to power some circuitry. You need to use a 600:600 isolation transformer. Go to www.microchip.com and lookup application note AN854. There in Figure 1 is an example of what it takes (their engineer's opinion) to communicate over the phone lines using a PIC and a few discrete components.

Pretty much any circuit today uses the transformer to isolate the product from the phone line. There are several alarm dialers on the market that use opto-isolators and P-mos relays to connect to the phone line. Did you look at the site that I listed on my first reply?

BobK

[Art]

You'll be wanting to run your pic at 20MHz to stand a chance of your phone system
recognizing the DTMF tones produced by PicBasic/Pro.
Don't forget to DEFINE OSC 20
The tones produced by the pic aren't a very pure sine wave.

An external DTMF generator chip would be best,
but I have used a 16F84 to dial numbers and navigate DTMF phone menu systems.
One project was an automated thing to retrieve my bank balance over the phone on payday.

[ultramegaok]

You'll be wanting to run your pic at 20MHz to stand a chance of your phone system
recognizing the DTMF tones produced by PicBasic/Pro.
Don't forget to DEFINE OSC 20
The tones produced by the pic aren't a very pure sine wave.

An external DTMF generator chip would be best,
but I have used a 16F84 to dial numbers and navigate DTMF phone menu systems.
One project was an automated thing to retrieve my bank balance over the phone on payday.

Thanks Art for the Tip
I will try at 20MHz.....by the way , I like your website......

[ultramegaok]

Hello, ultramegaok

You will not be able to send any thing out to the phone line through a bridge rectifier!
The only thing the bridge rectifier is good for, on a phone line, is drawing power FROM the phone line to power some circuitry. You need to use a 600:600 isolation transformer. Go to www.microchip.com and lookup application note AN854. There in Figure 1 is an example of what it takes (their engineer's opinion) to communicate over the phone lines using a PIC and a few discrete components.

Pretty much any circuit today uses the transformer to isolate the product from the phone line. There are several alarm dialers on the market that use opto-isolators and P-mos relays to connect to the phone line. Did you look at the site that I listed on my first reply?

BobK

Thanks BobK
I have read the website from your first reply which helps me a lot to undertands how telephones work, I was trying to avoid the transformer because I don't have one on hand rigth now, but I think I need to go to radioshack and get one. That seams the most safest way to connect the pic...... I let you now my progress...Checking AN854.