DTMF from a pic chip

L

lerameur

Guest
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
 
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"
 
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...
 
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...
 

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