Phone Line-powered Flashlight




What do you do when the house power goes out? Look for flashlights! But if you're as sloppy as I am, you're going to see that they are out of batteries since the last time the power went out.

Since, in 90% of the times, the phone line is still working even when the whole city has no light. This instructable will show how to make a flashlight that uses the phone line power. (Yes, the phone LINE delivers a small amount of current to your house)

Before I start, I'd like to say that I did not find anything forbidding me to plug this into my phone line, but you should check whether it's legal in your country and if using the phone line current is prohibited by the phone company's contract. (and take it easy on the comments. English is not my first language and this is my first instructable)

Don't forget to rate!

Step 1: What You Need

The materials to make the flashlight are:
1x Phone wire
1x Box to put everything inside
12x White LEDs (3.0V / High Brightness)
1x LM317L or LM317T (Voltage Regulator)
4x IN4007 (Diode)
1x 6.8K ohm resistor
1x 270 ohm resistor
(the 2 resistors values may change depending on your phone line - See step 4)

Sorry for the picture, I've made this project a couple of years ago (way before I found the Instructables website) so everything is already put together.

Step 2: Soldering It Together

So this is the schematic for the circuit.

My phone line delivers 48V DC and something around 20mA, and when the phone rings, it delivers 96V AC.
This works in a way that the phone line won't stay busy while the LEDs are connected and when you pick up the phone, the light goes off and allow you to use your phone normally.

-Solder all 12 LEDs in series (negative pin of a led to the positive of the next led)
-You will use the four IN4007 to make a Bridge Rectifier.
-Solder the negative pin of the last LED to the negative pole of the bridge and solder the positive pole of the bridge to the input pin of the LM317.
-To the output pin of the LM317 you will solder the 270 ohm resistor (R2), and to the adj. pin you will solder the 6.8K ohm resistor (R1).
-R1 and R2 will be soldered in parallel and then to the positive pin of the first LED.
-In the middle of the Bridge, where the ~ signs are, you will solder the RED and the GREEN wires that comes from the phone wire.
(The bridge is necessary to rectify the 96V AC when the phone rings)

Some phone wires have 2 more wires inside (yellow and black), we won't use them here.

Note: The third image is the schematic I got from LaserDave, I promissed I'd post it up, so here it is!
A want to point it out that I have not tried to build it from his schematic, so if you have any question look him up.

Step 3: Put It in a Box

I found a little plastic box to put the circuit in. I punched holes on a white cardboard and glued it on the opening to keep the LEDs in place.
It doesn't look good, but this was my first electronic project and I didn't know anything about it.
It will look good if you use a perfboard to solder the LEDs and even better if you find a 12 LED flashlight with a reflective lid to mount everything in.

I drilled a hole on one side of the box, put the phone wire through it, tied a knot and put glue on it so if I pull the wire, it won't break the red and green little wires.

Step 4: Test and Adjustments

You're done, just plug it in the phone line and enjoy! (also works with DSL lines)
It's not like a 100W light bulb, but it's perfect for when the lights are out!

These settings will give you a very bright light, but in some cases you might get busy line on your phone.
To fix that you can change the R1 and R2 resistors.

The higher is the R1 and the lower is the R2, the brighter is the light. But it's more likely to get busy line.
If thats your case, you can put a higher R2 resistor (330ohm).
If you still get busy line, put a lower R1 resistor (3.3K ohm or 1K ohm)

If you don't want to test a bunch of different resistors, just stick with R1 = 1Kohm and R2 = 270ohm. This will work for sure, but you will lose a little amount of brightness!

Any question, just leave a comment

PS: -I don't know if this is legal or not in your country, you should check it out yourself, please don't flood the comment page saying that this is illegal as if the World were ruled by your country's laws, because it's not!!
-I've built this and it works perfectly. I receive and make calls at any time when this is plugged to my phone line, no interference at all.
-Also, if your phone line is equivalent to mine, you don't have to change anything. If you really think any component is not necessary, give it a try and post the instructable so we can learn from it!

PS2: I am not incentivizing anyone to "steal" energy from the phone company. Use it with intelligence! If you keep it plugged for the whole day and 1000 people from your city do the same thing, the phone company will start charging for this energy and everyone loses.

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    176 Discussions


    2 years ago

    i see what you did in regards to the LM 317L, the output of the 317 is +, on the printed schmo, you have the op going to the cathode, i think the op should be going to the anode- please check



    2 years ago

    the 4 diode bridge seems to be reversed per the hand drawn schmo and the printed schemo??


    3 years ago



    3 years ago

    very good. thank you.


    6 years ago on Introduction

    Thank you, with this idea, I am running my stereo, computer, refrigerator and 2 savors, i cook my food in an electric oven now, man its awesome (i mean idea),
    only thing I couldn't figure out till now is how to market it!

    1 reply

    Reply 3 years ago

    Hi how can I contact you. Can you please mail me on

    So this is going to be a dumb question, sorry. I use VOIP and stream my TV, but I pay for Internet from Comcast (8ms ping 58 down / 11 up 98% of the time) Comcast also provides my phone service if I used their modem or pay for it. Question is, for emergency purpose only, if I use the land line wall jack to provide light or emergency calls, does that not constitute appropriate use in the USA?


    4 years ago on Step 2

    In the first schematic the leds are in the right polarity, but in the third image it looks bad


    5 years ago

    hi thanks for the idea now can u add a part to your project to make ur device senses that the current was cut off and light automatically ?


    5 years ago on Introduction

    how can i use the phone line to charge my iphone. I dont have a land line and I know there is power running through the wires even though I dont pay for it. Would I have to use a transformer to step it down. What is the voltage coming out of a wall charger for an I phone?


    5 years ago on Step 2

    Hi! The phone line delivers 54.5v and when the phone rings 55.3v.

    Should i do something different?

    Thx, Obrigado.

    1 reply

    Reply 5 years ago on Step 2

    Hi alpist.
    It should work just fine. You can always change the R1 and R2 resistor until you get the desired effect on the LEDs.


    6 years ago on Step 2

    hello.. u sadi that ur phone delivers 48 v DC n when phone rings , it delivers 96 v AC.. right..! can u plz explain how dis hapend??????? r else send me a link twhich related to this ....! as soon as possible
    thnku !


    6 years ago on Step 4

    quiero ver video youtube, como saber luz como parpadera o continua luz, me duda, soy persona sordo, necesita flashlight


    6 years ago on Introduction

    I have 8 pre-made LED circuits in the form of a circle which are currently connected to 3 Dcell batteries each. This was a marketing lamp in its former life. There are about a dozen LED lights per circle. How would I attach the phone line to this so I can not use the batteries?

    Would it be as simple as attaching the phone line to the +/-?


    7 years ago on Introduction

    illegal/criminal as far as I know!, check with your phone company, you can be cut off for stealing power.

    1 reply

    Reply 6 years ago on Introduction

    It's not. They are required by law to keep that voltage on there for 911 purposes. And it's not like you're powering a refrigerator. What qualifies me to say this? I worked for Bell South, I was the guy that installed the OC182's.