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need help about phone line

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alitex

New Member
hi all
i make project that can detect DTMF/SCK by sm8223 IC,but i want when i recieve call make hook-off to send some command by AVR controller (mega16),
is there method that i can make hook-off ?
thanks alot
 
Last edited:

dougy83

Well-Known Member
Connect a 470 ohm resistor across the line to take it 'off-hook'
 

audioguru

Well-Known Member
Most Helpful Member
A 470 ohm resistor across a North American telephone line will dissipate about only 0.21W which is not a lot. Use a 0.5W resistor in opean air and it will be fairly warm, not hot.
 

audioguru

Well-Known Member
Most Helpful Member
Different languages are strange.

A can of beer "opens", not a phone line.
A phone line goes "off hook".
If a can of beer goes off hook then you are plastered and should not drink any more beer.

But many weird things happen in Syria? Like hardly any alcohol in beer?
 

alitex

New Member
Different languages are strange.

A can of beer "opens", not a phone line.
A phone line goes "off hook".
If a can of beer goes off hook then you are plastered and should not drink any more beer.

But many weird things happen in Syria? Like hardly any alcohol in beer?

ok,thanks for right english,but really i don't drink beer;)
 

alitex

New Member
A 470 ohm resistor across a North American telephone line will dissipate about only 0.21W which is not a lot. Use a 0.5W resistor in opean air and it will be fairly warm, not hot.

i measured the current across 680 ohm/4W the value of current is 250mA at least, what is ur opinion about it?
 

audioguru

Well-Known Member
Most Helpful Member
i measured the current across 680 ohm/4W the value of current is 250mA at least, what is ur opinion about it?
Your country is very strange:
No beer.
Extremely high telephone line current.
I won't talk about your religion (Muslim?).

250mA in 680 ohms produces 42.5W which will quickly smoke a 4W resistor. Maybe the current is only 25mA.
Current is measured in series with the load, not "across" the load.
 

Mr RB

Well-Known Member
i measured the current across 680 ohm/4W the value of current is 250mA at least, what is ur opinion about it?

Put your current meter in series with your normal telephone. Then lift the telephone handset and see what the current is. That will tell you the current you need to use to simulate "off hook".
 

alitex

New Member
Your country is very strange:
No beer.
Extremely high telephone line current.
I won't talk about your religion (Muslim?).

250mA in 680 ohms produces 42.5W which will quickly smoke a 4W resistor. Maybe the current is only 25mA.
Current is measured in series with the load, not "across" the load.

ok right the current is 25mA
i'm sorry again but really i'm newbie ,but i talk about my self for beer
 
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