Emergency Phone Line Lamp




About: I'm an electronic engineering student. I don't usually have much spare time but I like to work on random projects to keep myself entertained. I hope you like them!

Summer is officially over, and good weather has gone with it, heavy storms are something inevitable for most of us and thus we need to be prepared. Now, before you start buying hot chocolate in bulk, I'm talking about power outages, which can last for hours, specially if you live in rural areas.

It's is very important to be prepared since our lives are closely bonded to electricity, which we usually take for granted. The list provided below is an example of what you should have in your "power outage kit".

Among other things, a source of light is one of the most important, most of the injuries during blackouts are caused due the inability to see what's in front of you. Flashlights and candles are a good choice, but they only can work for a limited amount of time or until you run out of batteries. But not all the power goes out during a blackout, there are devices which will still work. I'm talking about the telephone, which runs on power from the telephonic company, enough to power some LED's for an unlimited amount of time.

In this instructable I'll show you how to build a simple yet effective LED lamp which plugs directly into the phone jack.

Disclaimer: You'll be taking extra power from the telephonic company, although this probably won't be illegal, it's a questionable practice. You might end up with some technicians knocking on your door if you suck too much power or short the lines due to defects in your circuit, paying for it doesn't means you can abuse of it.
This project involves working on lines which can reach voltages up to 90V AC, probably enough to give you a slight shock, specially if you work with wet hands. Disconnect the circuit when working on it.

Step 1: Materials and Tools

Making this lamp is extremely simple, you only need a couple of materials and some basic soldering skills.


  • <0.5m of LED strip (low power LED's = or < 20mA)
  • A piece of plastic (to stick the LED strip)
  • 1kΩ, 1.2kΩ 1.5kΩ or 1.8kΩ Resistor (check table at 2nd step)
  • 330Ω, 470Ω, 560Ω or 680Ω Resistor (check table at 2nd step)
  • Telephone jack (female) (optional)
  • Telephone cable
  • 3 position toggle switch (for adjusting power or 2 position if you prefer a single mode)
  • Plenty of shrink tube
  • Insulated copper wires
  • 4x 1N 4007 diodes


  • Soldering iron
  • Multimeter (extremely recommended)
  • Drill (optional)

Total cost of the project: <10€

Step 2: Step 1: Calculations

LED strips are separated into modules, in other words, it can be cut every three LED's, with convenient copper pads to make connections between them.

My telephone line runs on 50V DC (this number might vary depending on your provider, I obtained it testing my line with a multimeter, but they can go all the way up to 90V DC), this is a nice voltage to work with, but there's a problem, and it is the current. You can only draw a very limited amount of current before the line starts to malfunction, so we need to make some modifications to our LED strip in order to make it work in series, taking advantage of the voltage drop of each individual LED to use as little current as possible.

To do this we'll use a number of individual modules equal to our telephone line voltage divided by 3.3 (rounded down) and divided by 3 (rounded down again). In my case I have 50 volts, 50/3.3 = 15, 15/3 = 5.

You can use the table provided to figure how many modules you will need depending on the voltage, also I included the values for the resistors for the "High" and "Low" power modes. The value of the resistors changes because the voltage drop of the LEDs is usually a bit lower (than 3.3 volts) when they're not under full load, and thus the resistance must be increased in order to compensate for this.

Although this design will probably work with almost any phone line it is important to measure the voltage of your line and check the table to end up with an efficient and properly working circuit. If you don't measure the voltage and follow the table you risk your circuit being too inefficient and drawing too much current, probably disabling the line while the circuit is plugged in.

Step 3: Step 1: Cutting the LED Modules

After checking the table we obtain the number of individual modules we need (5 in my case) we cut the LED modules carefully, trying to leave the pads intact, since they'll be useful to make connections later on.

Step 4: Step 2: Sticking the Modules Down

Now it's a good time to stick the modules into a flat plastic (or similar) surface, I mark the position with a sharp tool, leaving 2 Cm between each one and a bit of extra space for the switch and just in case I want to screw it to an arm lamp.

Sticking the modules will help us during the next step, not only because they won't move and it'll be easier to work with them, but also because the plastic surface will act as a heatsink when soldering.

Step 5: Step 3: Soldering and Desoldering

After the modules are stuck to the plastic we need to desolder the resistances, they are no longer useful because we're not working with 12 volts anymore, we bridge the pads in which they were placed with a blob of solder.

To connect the LED's in series we'll connect the negative pad of the module to the positive pad of the next one, and so on, we'll do this by using tiny pieces of wire, which can be epoxied down to avoid unsticking the modules in the future.
I solder a larger piece of wire to the last negative pad at the end of the array.

Step 6: Wiring the Input Connector

We can connect the lamp to the phone line in two different ways, one is by peeling of the insulation of a male cable and soldering it to our lamp, the other is to solder a female connector to it, that way we'll be able to use any cable of any length without having to be attached to our lamp at all times.

I bought this female-to-female line connector and pried it apart, then I cut the cables, peeled the insulation and soldered the green (positive) and red (negative) wires to another cable in order to have a reasonable length to work with. The rest of the cables are trimmed down.
Phone wire cables are thin and fragile, I used plenty of shrink tube to keep the connections from moving. I used a larger piece of shrink tube to cover the whole connector.

Note: Notice the color codes will probably change from country to country (I live in Spain), the best option is to check with a multimeter until you find the biggest voltage between wires and trim the rest.
I've added a table with the most common colors, I took it from the "ElectroDroid" app.

Step 7: Placing the Switch

The switch needs to be located in a convenient place in order to be toggled easily without moving the wires connected to it, a loose switch could debilitate the wires and break them eventually.
I have chosen to install the switch on the plastic surface along with the LED, to do this I make a hole using my soldering iron, although I recommend using a drill to do this unless you're in a well ventilated area.
I pass the switch to the hole and hold it with a nut and a washer.

Step 8: Wiring the Switch

For this lamp I used a three position toggle switch, this will allow me to choose between two power modes. I did this to bring down the brightness in case I need to use it with a line which can not supply enough current.
Wiring the switch is very simple, the middle pin is the common, this will be connected to the positive wire (green), the other leads of the switch will be connected to two resistors, one will have a value of 1k, and the other should be around 330 and 560 Ohms, the other ends of the resistors are joined toghether, and are connected to the positive input of the LED array.

Step 9: Final Connections:

For the last connection we solder the negative wire coming out from the jack to the negative wire coming out of our LED array.
Again, we use plenty of shrink tube to secure our soldered wires.

Step 10: Testing and Troubleshooting

To avoid accidental damage to your phone line it is advisable to use a power supply first to verify the circuit is working correctly.
After connecting the phone jack to the phone line the LED's should light when flicking the switch to a non neutral position.
When using the 1k resistor the phone line should still work, try to call and confirm the phone works correctly when the device is in use, it is possible that the phone stops working when you switch to a smaller resistance. If this happens and you haven't followed the table at step 2 now it's a good time to do it.

Common problems:
-I connected it, but it doesn't works.

Use a multimeter to verify there's a voltage between the switch and the negative wire.

If there's no voltage:

  • Check the line it is connected to has voltage
  • Check your circuit for shorts (continuity mode)
  • Check the cable you're using isn't damaged.
  • Check the polarity is correct, you might have reversed the wires when soldering them.

If there's voltage:

  • Check for open circuits
  • Check the switch is connected properly
  • Check the polarity (see next step to solve this)

It works but the phone line doesn't:
Are you using a 1k resistor?
Yes (weird): See note below.*
No: See note below.*

*Note: This could be an indicative your line has quite more than 50V DC, therefore your circuit is drawing too much current, check with a multimeter, after you got the voltage refer the table at the 2nd step, adding more LED modules and changing the resistances if the table indicates so.

After measuring the voltage at the line you get ~74 volts, you must head back to step 2 and check the table. According to it you should use 7 individual modules instead of just 5, you also have to increase "high power resistor" to 470 Ohms and the "Low power resistor" to 1200. If the last number is higher than 5 it is advisable to jump to the next voltage (e.g: 76V get's rounded to 80V)

It is very advisable to check the voltage of the line from the beginning, since not every line has the same voltage, but I understand not everybody has access to a multimeter.

Step 11: Extra Features and Improvements.

Now your circuit is finished and working you can get creative and attach it to a lamp structure. This step is optional, but can be quite convenient.

After some testing I noticed the polarity can be reversed depending on which cable I use, leaving the circuit inoperative if I used the wrong cable. You can leave the circuit as is if it works fine, but if you are going to use it with multiple jacks and cables it is recommendable to fix this, as I did. Solving this problem is extremely simple, we just need to add a bridge rectifier. This simple circuit takes any polarity in and redirects it so we always end up with a positive voltage on a side and a negative voltage at the other.

First we take 2 1N4007 diodes, and we join the cathodes (the side with a white strip) twisting their leads together, we repeat the operation with 2 more diodes, this time joining the anodes (the black side), we should end with something exactly like in the 2nd picture.

Next, we take one of the leads of our pair of diodes and join it to another lead of the other pair, this way we connect the anode and cathode of the diodes (see 3rd picture). We repeat the operation with the remaining leads which aren't joined together, we should end with the arrangement depicted on the 4th picture.

We cut, strip and tin the cable, the two wires coming from the line will be connected to the anode-cathode pairs, the polarity isn't important here, so you can connect it either way (see pictures 1 and 6).

The wires coming from the lamp need to be connected according to their polarity, the positive wire (the one going into the switch and into the positive side of the strips) will be connected to the cathode pair (white strip), the negative wire will be connected to the anode pair (black side) (see pictures 1 and 6).

After the connections have been made I use plenty of shrink tube to prevent wires from moving, this will make the connection much more stronger.

Step 12: The End

Now you've got an unlimited source of light in case of emergency, hopefully it will be useful during your next blackout.

Be safe and be prepared.

Thanks for watching.



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    68 Discussions


    3 years ago

    Wasn't there a "princess" phone with a light up dial that got the power from the phone line?


    3 years ago

    Excellent instructable. Unfortunately, this doesnt work with Fios or lightpipe or any other fiber optic system.


    3 years ago

    I can't believe this isn't against the terms of supply of telephone connection to your property. You risk disrupting that service which in the event of a power cut could be extremely risky, worse you might disrupt the telephone service to others who could be vulnerable.

    I think this is a very bad idea. a better solution would be buy a wind up torch or lantern.

    5 replies
    Mark 42ianheavy

    Reply 3 years ago

    You can't disrupt the phone service.
    Do you think they don't have protection against short circuits?
    If you put a heavy draw on the system (like a bunch of incandescent lights) it will look like a short, and the phone company system is designed to tolerate short circuits.

    Think about it - if the phone system was crippled every time some goofball do it yourselfer tried to install a phone jack incorrectly... we would all be in trouble.

    (Noy all DIY people are goofballs, but the system is goofball tolerant).

    ianheavyMark 42

    Reply 3 years ago

    Maybe in your part of the world, do you think all phone systems are as well engineered as the UK for example? I think not.

    I have seen equipment go up in smoke, because a fuse didn't blow at the amperage it was meant to blow at.

    This project isn't making a mistake, it's deliberate abuse of a service.

    Mark 42ianheavy

    Reply 3 years ago

    How many watts does an LED lamp draw? How many watts does your phone draw?
    What dou you think happens if you short out the line?

    ianheavyMark 42

    Reply 3 years ago

    I looked at the costing of the project the author gave. For that money I could get delivered a wind up lantern. Which as I said earlier is a much better solution.

    Any project that is relying on the safety factors built into a utility service is wrong in my view. As I said earlier I have seen fires caused beacuase a fuse didn't blow at the right amperage.

    Mark 42ianheavy

    Reply 3 years ago

    I've worked on phone system built from the late 1800's to the late 1980's.
    They are all designed to be idiot proof.

    I would expect cable TV and any other utility is designed so that if a customer shorts it out, or accidentally feeds back 110V house current into it, the company headquarters won't erupt in flames.

    The power company is the one that has the most difficult job protecting against people feeding back into the grid. But I expect they will be going to some sort of protection at the meter, now that more people are buying generators and solar systems.


    3 years ago

    you folks need to understand that you are drawing power from the backup batteries that the phone system typically uses to keep the lines going in a power outage. now i understand this varies more and more since many people are switching to phone services from the old traditional POTS/copper wire landline service, where the phone company maintained the batteries and they system, to a local battery at your point of phone service to your home or building.. the batteries in that case, IF any, are local and much smaller... so drain away your resources at your own risk...

    4 replies

    Reply 3 years ago

    In the town where I live there are no backup batteries or generaters at our central station and during a blackout there are 200,000 people without phones so we are instructed where to walk to so we can use a phone.


    Reply 3 years ago

    I doubt that 200,000 people are expected to walk "to use a phone" during an outage. What's powering the emergency phones? And how long are the queues of people for those few phones for a "town" of 200,000 people? Hmmm...


    Reply 3 years ago

    Michael Bloomberg our billionaire mayor apologized to us all saying he was sorry he just assumed we had backup power. A few years later when hurricane sandy wiped out 2/3 of the neighborhood he was quoted as saying "you see good thing we didn't have telephone power to your neighborhood, the salt water could have caused telephone fires!" Our town has 4.4 million people so we are told to , and get this! "walk to a trusted friend to use the phone" Welcome to new York city. You are not the first person who thought this is insane, even people who live a mile away did not believe it until the so called apology came.


    Reply 3 years ago

    As I previously stated, there are no batteries in AT&T networks. They use diesel powered generators to power the lines during any power failures. The battery backups that are in a persons house are for if they have VOIP service, that is Voice Over Internet Protocal. The phone company still powers the lines to your house, but, you need those batteries to power the equipment in your house.


    3 years ago

    SERIOUSLY not a good idea. Even a minimal amount of current draw on that line will be interpreted by the telco switch as an “off hook” condition, which means allocation of resources to your line to allow for a phone call. NOT a good idea.

    Also… TELCO sends a high voltage burst down the line to signal a “ring” condition. If not anticipated and handled properly, it can damage illegal, parasitic equipment.

    However, this lamp is a good idea, just power it with a deep cycle 12V battery you keep on a float charge for emergencies.

    4 replies

    Reply 3 years ago

    I worked for AT&T as an outside tech for 25 years. There are no batteries. They use diesel powered generators to power the line during a power failure. If you use the additional 4 diodes in the circuit it will just appear to the phone company's equipment that you have installed another phone on the line. The nominal voltage on the line is 50VDC. When the line rings there is an additional 120VAC added to it but at a very low amperage. You wont get killed, BUT IT WILL SHOCK YOU!!! I would suggest that you do not leave this plugged in, but keep it around so you can plug it in if your power goes down.

    Mark 42bluesea8

    Reply 3 years ago

    When I worked in a switchroom, there were HUGE batteries in the basement.
    The system ran on those batteries at 48V DC.
    The generators kept the batteries charged when the power company went down.

    If you can plug an ordinary phone into a jack, 48V is there.

    Mark 42aviram

    Reply 3 years ago

    You can't disrupt the phone service.
    Do you think they don't have protection against short circuits?
    you put a heavy draw on the system (like a bunch of incandescent
    lights) it will look like a short, and the phone company system is
    designed to tolerate short circuits.

    Think about it - if the
    phone system was crippled every time some goofball do it yourselfer
    tried to install a phone jack incorrectly... we would all be in trouble.

    (Noy all DIY people are goofballs, but the system is goofball tolerant).


    Reply 3 years ago

    As for the UK, we had a broken phone in the house partially shorting our line for quite a number of months (also knocking out our FTTC over POTS broadband) and they still didn't find it after 7 (yes SEVEN) engineer visits, we did get put on a nice new line to the exchange though. But I do agree, it probably isn't best practice. Our local exchange has diesel generators too to top up the batteries.

    spark master

    3 years ago

    I can not find my post where I say what many have already said.

    1) If you have fiber to your residence you have no "battery", hence no power on the line. YOU provide the "battery". If you are Very Very Lucky there is an actual Battery Back up on the line!!!!!!

    2) If you have OPtimum or some cable provider, they also do not have Battery that is why they plug their eqiopment IN your ac outlet.

    Does every one got that.

    If you have battery from your provider, it is a back up Batt and will die after 1 weeek of LOW usage.

    Therefore buy a rechargable battery

    figure out how to solar charge it.

    go for it.

    This would have worked really really well 10 years ago, not today.

    If you really want to do it fast. Buy solar garden lights, put an on off swith in them, let them charge for 2-3 days TURNING THEM OFF AT NIGHT.


    Buy a very cheap chinese made LED lantern with C or dare I say it D cells in them. These will last a very very long time indeed.

    This was a nice instructable no matter that it is very limited in usability, because it will cause people reading the commentary to learn "stuff". Then since they now realize hey I actually might want to be able to see in a black out read the comments, see the issues and either build something cool, or just go buy a bunch of inexpensive long lasting lights, battery operated and solar rechargeable.

    Here is a thought. Over the years I have had manually rechargable (magneto type) flash lights and am/fm/sw radios. They never work well at all. On alkaline batts or wall socket sure. But the recharging systems stink and the magneto is a piece of crap that fails really really fast. Complete crap. I have tossed 3 radios and more then 4 flash lights.

    I have also done the flash camera spent CF lamp tricks and they do woerk, and are kinda nice, but getting the flash units is harder everyday as less people use disposable cameras.

    And if you use a fresh CF and a D cell or better 2 D cells, you can get quite a bright light. It will work for a month.

    As a survivor of Sandy w/o electric for 2 weeks, like the Boy Scouts tell us,



    Oh yeah CF Compact Fluorescent, Spirallamps.


    3 years ago

    Unfortunately, in rural areas you have quite a voltage drop, there's 8 miles of copper between me and the exchange.