DTMF from a pic chip

06 May 2008 18:21:54

lerameur

Hello,

I finally got my circuit working... well almost.
I use a pic chip with picbasic pro, I output DTMF and this goes
through a filter shown in picbasic manual:
http://www.melabs.com/resources/pbpmanual/5_17-5_21.htm
From my scope I can see some 40v spike at the pin output and after the
filter I do not see much maybe a few volts.
This goes directly to an audio transformer.
Is it normal to have 40v spike (the signal looks pretty nice). WHen I
put a modem speaker at the pin output I can hear the dialing and maybe
a third in strenght (sound) after the filter. At the output of the
transformer I have an AC 250v capacitor. The pichip dials my phone,
and I receive maybe 50% of the calls.
Should I be using the filter? (I am not using an amplifier as
mentionned in the manual)
Is the 40v good to put directly on the transformer?
Also from the speaker I hear a lot of background noise

thanks
k

06 May 2008 21:35:44

Jamie

Re: DTMF from a pic chip

lerameur wrote:

> Hello,
>
> I finally got my circuit working... well almost.
> I use a pic chip with picbasic pro, I output DTMF and this goes
> through a filter shown in picbasic manual:
> http://www.melabs.com/resources/pbpmanual/5_17-5_21.htm
> From my scope I can see some 40v spike at the pin output and after the
> filter I do not see much maybe a few volts.
> This goes directly to an audio transformer.
> Is it normal to have 40v spike (the signal looks pretty nice). WHen I
> put a modem speaker at the pin output I can hear the dialing and maybe
> a third in strenght (sound) after the filter. At the output of the
> transformer I have an AC 250v capacitor. The pichip dials my phone,
> and I receive maybe 50% of the calls.
> Should I be using the filter? (I am not using an amplifier as
> mentionned in the manual)
> Is the 40v good to put directly on the transformer?
> Also from the speaker I hear a lot of background noise
>
> thanks
> k
Assuming you have the correct voltages around the PIC, you have
something seriously wrong!
It almost sounds like you are some how getting part of the phones
voltage in there.
I don't know what the voltages are these days, but it use to be
50 volts on the line while on hook.
Maybe you should be using an isolator.

http://webpages.charter.net/jamie_5"

07 May 2008 05:34:41

lerameur

Re: DTMF from a pic chip

On May 6, 9:35 pm, Jamie
<jamie_ka1lpa_not_valid_after_ka1l...@charter.net > wrote:
> lerameur wrote:
> > Hello,
>
> > I finally got my circuit working... well almost.
> > I use a pic chip with picbasic pro, I output DTMF and this goes
> > through a filter shown in picbasic manual:
> >http://www.melabs.com/resources/pbpmanual/5_17-5_21.htm
> > From my scope I can see some 40v spike at the pin output and after the
> > filter I do not see much maybe a few volts.
> > This goes directly to an audio transformer.
> > Is it normal to have 40v spike (the signal looks pretty nice). WHen I
> > put a modem speaker at the pin output I can hear the dialing and maybe
> > a third in strenght (sound) after the filter. At the output of the
> > transformer I have an AC 250v capacitor. The pichip dials my phone,
> > and I receive maybe 50% of the calls.
> > Should I be using the filter? (I am not using an amplifier as
> > mentionned in the manual)
> > Is the 40v good to put directly on the transformer?
> > Also from the speaker I hear a lot of background noise
>
> > thanks
> > k
>
> Assuming you have the correct voltages around the PIC, you have
> something seriously wrong!
> It almost sounds like you are some how getting part of the phones
> voltage in there.
> I don't know what the voltages are these days, but it use to be
> 50 volts on the line while on hook.
> Maybe you should be using an isolator.
>
> http://webpages.charter.net/jamie_5"

I think I might got the probe switch to 10x instead of 1x.. that would
explain. I will check it once I get home...

07 May 2008 06:11:17

lerameur

Re: DTMF from a pic chip