Phone Jack Power Taker

[cannon701]

For this thing I have to have two resistors a regulator and a bridge rectifier. I am just wandering what a regulator does.

 

[Mikebits]

Trying to power something from the phone line is just a bad idea. Your Telco would not be to happy either. The link below is provided for reference.

Telephone interfacing circuits

 

[LTX71CM]

Are you trying to design this circuit yourself or are you following a schematic? If you're following a schematic, can you post it?

What kid doesn't drool at the thought of a leech powered AM telephone tap... If that is what you're making be courteous, your neighbors will be able to hear what you can. I say have fun but not in a distasteful manner. Also note that if you plan to install it on someone's line other than your own there are legal consequences.

 

[audioguru]

It is illegal to "steal" power from a telephone line and nobody should try it.
A telephone line that is not in use should not draw any power.
A fairly low amount of power drawn from a telephone line causes it to go off-hook. If the line remains off-hook for a certain duration without dialing then the line is disconnected at the central office to prevent a shorted line from causing too much power draw.

 

[cannon701]

**broken link removed**

 

[cannon701]

@Audio the thing is, this isn't gonnah be used for power all the time. Just in black outs.

 

[Nigel Goodwin]

@Audio the thing is, this isn't gonnah be used for power all the time. Just in black outs.

So you think it's OK to steal during black outs?.

It's illegal to do, and you can get very little power anyway.

 

[LTX71CM]

If you're just after power and nothing else, listen to Nigel. You're far better off just using a battery instead of trying to leech from the telco.

 

[audioguru]

Oh. You are in India or Nigeria where the electricity is not reliable.

The resistors on your LM317 are not connected correctly but if they are then the current of the LM317 might cause your telephone line to go "off hook" and then the central office will disconnect it. A small current drawn from a telephone line causes it to go off hook. If dialing is not done soon then the central office thinks the line is shorted and disconnects it.

 

[Mikebits]

Isn't the ringing voltage something like 90VAC?

 

[audioguru]

The ringing voltage is 90VAC on top of the 50V from the on-hook telephone line, in North America. So the peak voltage is 177V which will destroy the LM317. Who knows what the ringing voltage is in the country that does not have reliable electricity?
The LM317 regulator's operating current will load down the line so much that the line will probably go off-hook and will "answer" the call, but the LM317 will probably cause the line to go off-hook before the line begins to ring.

I don't know if the LM317 is supposed to power the AM transmitter.

 

[audioguru]

Edit: why are there two threads that are almost the same?

 

[KeepItSimpleStupid]

Apart from being illegal if you don't use an FCC registered device to connect to the line there isn't much power there. Talk battery is between 20 and 40 mA and the line is at 5 V or so when on hook. 5*0.4 or 0.2W is not a lot of power. The linear regulator is very inefficent, so you have even less.

You need a battery backup. Sorry. That's the way it is.

Furthermore, "I need x volts at x current. Can I get this from an (On hook | Off Hook) phone line? would have been a better starter sentence.

 

[cannon701]

OK I just decided to build a 9 volt battery charger for my mp3. Using a 5v regulator and a usb cord and of course a 9v battery. Then I put it into a hobby box(Think that is what it is called).

Anyways, I am thinking of selling some more to my friends. However, I think it would be cooler if I could make a rechargable batterypack. How could I make it recharge when connected to a usb port of a computer.

 

[audioguru]

Go to the website of a battery manufacturer like Energizer or Duracell. Then look at the datasheet for an alkaline 9V battery. Its voltage drops to 6.5V (when an ordinary 5V regulator fails to regulate) in about 50 minutes with a load current of only 250mA. You need more time and more current so a 9V battery is much too small.

A rechargeable Ni-MH "9V" battery is actually 8.2V and drops to 6.5V in about 20 minutes with a load current of 250mA.

Doesn't your MP3 player already have a rechargeable battery and a charger?

 

[cannon701]

So in other words, any 9v battery I get will only be good for 50 minutes?
And yes it does but its usb based for cpus. It has radio on it and radio uses alot of energy on some stations. So I am making a battery pack.