This Instructable tells how to build a LED flashlight that is connected to and derives its power from the telephone line. If you can’t take the time to read this, at least read the conclusion at the end. First off, I must warn the reader that this is illegal, foolish, dangerous and can cause problems with the phone line. The instructable has over 146 comments that people have written that tell various reasons that they believe it should or should not be used. I will give a few true facts which may be disputed but are still true facts.
LEGAL The federal Part 68 rules govern phone lines and say that connecting such devices to the phone line is not allowed. Connecting a device that draws current from the phone line can cause the telephone company’s equipment to sense that there is leakage on the line, and cause the equipment to initiate a trouble alarm and can cause the line to be temporarily or permanently disabled. The trouble alarm may cause the telephone company to dispatch a repairman to find the ‘leakage’, and when they find that it is caused by your light, they will bill you for the repair time. In my area, this is about a hundred dollars for an hour. I will be truthful and say that the telephone company may not do this, but may disable the line instead. Here is a writeup about the Part 68 regulations. This LED light violates the following rule (which is found in this link, and I quote verbatim):
Dc on-hook resistance is required to be greater than 5 megohms for an applied voltage of up to 100 V and greater than 30 kilohms for an applied voltage of up to 200 V (see Figure 3). The telephone companies use an automated insulation test system as part of their maintenance routine. If the dc on-hook resistance of an attached piece of equipment is too low, the line is interpreted as being damaged, and repair procedures are initiated. The dc resistance requirement prevents false service alarms.
SAFETY The circuit uses a LM317 which is rated for a maximum of 35 volts. The telephone line has voltages that range from 48 to 56 volts when the receiver is on hook, to 90 volts RMS or 150 volts peak during the time when the phone is ringing. These far exceed the maximum for the LM317 and could cause it to overheat and burn out. The most unsafe time for a phone line is during a thunderstorm when a lightning strike even miles away can cause extremely high voltages and currents in the phone lines, and cause anything connected to it to catch fire.
Technical This LED light is supposed to steal enough current from the phone line to light the LEDs but not enough to cause the equipment at the central office to sense that a phone is off hook and trying to make a call. The LED current is supposed to be around ten milliamps, but this causes two problems. When the CO (central office) senses the phone is on hook and ready to receive a call, the CO sends out a ringing current of 90V AC (RMS) which is supposed to cause the bells to ring. But the LED light is loading down the line, and the ringing current goes into the light instead of the bells, and the bells ring weakly or not at all.
Another odd thing can happen during the time the ringer current is being sent. While the ringer current is being sent, the CO equipment is sensing if the phone is picked up or goes off hook. When the ringer current goes through the LEDs, the CO immediately senses that the phone is off hook. The ringer current is immediately stopped and the CO connects your line to the calling party. But now the voltage is too low to keep the LEDs lit, so the current drops below that required to make the CO sense that the phone is off hook, and it immediately disconnects the call. What the person calling your number hears is a very short ring, like a BRIP!, then nothing, and after ten or more seconds, he then hears dial tone, like the phone is ready for him to make a call. In other words, it seems like the call didn’t go through.
Confusion The LED light will not work when your telephone is off hook and making a call. It will only work when the receiver is on hook or “hung up”. Suppose you plug the light in and it works. Then you take the receiver off hook to make a call. Everything works okay, until you hang up the receiver. As soon as you put the handset into the cradle, the switch disconnects the phone from the line. The phone line starts to rise to its normal on hook voltage, 48 volts. But the LEDs turn on before it gets to the full voltage. The equipment in the central office can get confused and think the phone is still off hook and trying to make another call. The equipment gets confused and tries to send dial tone, but the LEDs go out again. So the cycle repeats on and off, and never does get to a stable state. I’ve seen this happen with some things I’ve connected to the phone line.
DSL Line Your phone line also carries the DSL signal to give you your internet connection. When you put this LED light on the line, it loads the line down so that your DSL modem receives a weak or no signal. Don’t be surprised if your internet connection stops working when you put this light on the phone line.
Another Safety Issue Many people nowadays have other services that furnish your telephone line service. If your telephone line is furnished by your cable TV company, then the telephone line is connected to the cable coming into your house. But the cable does not furnish your telephone with power. The telephone line is typically connected to an adapter box that gets its power from the wall. There is a small battery inside it that will keep it running for some time if the electric power goes out. If you connect the LED light to your phone line, it is using the power from this battery when the power is out, and the battery will be dead much sooner and you will not be able to make a phone call during the power outage.
VOIP Some people have switched from regular POTS (plain old telephone service) to VOIP (voice over IP). This is where your telephone is connected through the internet, with adapters such as the magic jack. The telephone line furnished DSL but there is no telephone dial tone and no telephone current. So if you plug your LED light in, it will not light up.
Conclusion I could go into more detail about this, but I’ve given enough reasons why this LED light is a really bad idea (I could comment about old rotary dial phones, but almost no one uses them today). The 146 or more comments left by others show that many other people think that it is a really bad idea. Don’t be foolish and attempt to build this project. You’re just wasting your time and taking risks that you shouldn’t take. Let some other fool make the mistake and when you read about it in the comments you can say, I’m glad I didn’t build this LED light.
Back to experimenting…