DTMF from a pic chip
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Posted by lerameur on May 6, 2008, 9:21 pm
Please log in for more thread options 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 | |||||||||||||||||||
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Posted by Jamie on May 6, 2008, 9:35 pm
Please log in for more thread options 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" | |||||||||||||||||||
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Posted by lerameur on May 7, 2008, 8:34 am
Please log in for more thread options On May 6, 9:35 pm, Jamie
> 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... | |||||||||||||||||||
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Posted by lerameur on May 7, 2008, 9:11 am
Please log in for more thread options On May 6, 9:35 pm, Jamie
> 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... | |||||||||||||||||||
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>
> 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