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Monitoring phone in use via serial PC

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CyberAle

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Hi all!

Sorry my english! :oops:

I need a circuit to monitoring the use of the phone: in use (off-hook), not use (on-hook). Only this 2 state. And, the circuit need to send a sinal like "1" or "0" to PC's serial.

Do I need use the MAX232 to make a interface with PC's serial? How?

Thx!!
 
In the US phone line voltage on hook is 55v.. off hook 6v. You could monitor with comparator circuit . I would use opto isolators to keep phone line surges from getting to pc.. Phone line voltage when ringing is 100v in US...
 
OK. In the Brazil (i'm from) is 48V on hook and 6V~10V off hook (i don't know right).

But, my problem is to project the circuit to compare and send a sinal to PC's serial.

Can you help me?

Thx!
 
well, using a resistor-devider you could have a transistor turn on at 48V and turn off at 10V...

For example, if you pick resistors to device the voltage by approx 65 then 48V would give 0.73V on the transistors base, causing it to switch.
while 10V would give 0.15V on the transistors base, so it won't switch...

Use the transistor to switch a 5 - 10V signal on and off and feed this to one of the handshaking lines of the pc's serial port, You can poll the handshaking lines at any moment...
 
Here's a page with a lot of different phone schematics. **broken link removed** Figure out how to get these interfaced to the serial port and you're set! :wink:
 
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