What do you do if the power is out and you need to charge your cell phone to make an emergency phone call? Don’t worry. There are plenty of potential power sources all around you. One of them is the phone line. In this instructable, I am going to show you how you can use the phone line to power your small electronic such as your phone or other USB devices in an emergency.
Note: This project is intended for emergency situations only. Please be aware of applicable local laws regarding phone lines in your area.
Step 1: Background Information: Power in the Phone Lines?
You may have noticed that corded phones don't need to be plugged into an electrical outlet. That is because they get all the power that they need to operate directly from the phone line itself. The phone company sends this power directly to your house through a pair of dedicated wires that connect to your phone jack. When the phone is not in use, this is a constant DC signal (about 50-60 volts). When the phone rings, the signal is a 20 hertz AC signal (about 90 volts). When in use it is a modulated DC signal (between 6 and 12 volts).
The phones lines even have power during a blackout in most cases. This is because the phone company maintains their own backup power system. Your phone lines may be powered even if you don’t have a land line service set up.