Simple External Telephone Ringer

Intro: Simple External Telephone Ringer

This is a simple external ringer for a landline telephone. Have you ever missed an important call because you didn't hear the phone? Or maybe you'd rather not wait by the phone for that special someone? Then this is exactly what you need! This ringer will allow you to hear incoming calls throughout the house or even outside, hopefully giving you enough time to actually answer.

STEP 1: Parts

• Piezo buzzer - I purchased a 12V 108 db buzzer from Radioshack. Get one that will be loud, or quiet enough for your purpose. A little louder would have been better for mine.

• Transformer - You need to step down the voltage from the phone line to power your buzzer. I tested the ringing voltage on my line at 120VAC, so I used a 12V 450mA transformer (Catalog #: 2731365 at Radioshack). The voltage can vary so make sure you have enough power for your buzzer.

• Capacitor - This is block the direct current from the transformer. If you don't use one the phone company will read that the phone is off the hook and everyone will get a busy signal when they call you. I used a 1µF metalized film capacitor.

• Rectifier - I used a bridge rectifier for this, but a single diode will work. You might wish to add another capacitor to smooth the output, but it isn't necessary.

• Project Enclosure - You will need some kind of housing for your ringer. I used a 5x3x2'' aluminum project enclosure (Catalog #: 2700238 at Radioshack)

• Miscellaneous - Solder and soldering iron, electrical tape, and some mounting screws. I also used heat shrink tubing.

STEP 2: Circuit

It's a very simple circuit. When a call is made, an AC signal between 60 and 120 volts is imposed over the DC loop supply. When the answering party picks up the phone, current is drawn from the loop supply and signals the ringing generator to de-engergize.

The capacitor is placed in series with the primary winding of the transformer to prevent it from drawing direct current and signaling that the line is busy. When a call is received the AC voltage is stepped down and rectified to power the buzzer.

If you don't use a circuit board make sure that all of the connections are insulated. I used the heatshrink tubing for this.

STEP 3: Construction

Arrange everything inside the project box and mark where you need to drill the holes. When you're drilling metal it helps to make an indentation with a punch to guide the drill bit.

You will need a small hole in the side to run the wires out of, and small holes to bolt the transformer and buzzer in and holes to mount the box with. I also drilled holes in the top of the box so you could hear the speaker better. Make sure that they are small enough that nothing can get inside.

Once you have that you're ready to hook it up.

STEP 4: Finishing

Mount the box somewhere out of the weather and install the cover, then run the line to the interface box. You can also connect your ringer anywhere on the line if you prefer.

There are just two wires on the phone line and polarity doesn't matter. Just be careful not to disturb the other wires while you are connecting it, and be very careful because there is 50 volts present at all times. You should disconnect the the phone line while working on it.

Once you finish, have someone ring your line and test it out. That's it! Thank you for reading.

Comments

[cgosh]

To view the schematic drawing (without having it covered by photos) just click on it to see a popup version.
The transformer is shown wired backward. The "high-voltage" winding is many turns of fine wire, the 12-volt side is a few turns of heavy wire.
When choosing a bridge rectifier, the author is right that a 50 volt version should be fine, but I'd go with a 200 or 400 volt version. It's only pennies more than the 50 volt version and may be easier to find. See my next comment.
Back in the day, the phone company restricted homes to a maximum of 5 phones, because the ringers required far more current (power) than modern designs. They were actual coils and magnets rather than modern low-power electronic noisemakers. If Ma Bell discovered you had an extra extension phone, they'd simply raise your bill $2 a month to cover it. A buddy had a ham shack behind his garage, had an extension phone inside, but didn't want the phone company to know he had it. So, he hooked up a pair of neon lamps to the phone line. When talking, they did nothing, but when ringing, they alternately blinked. Since neon lamps require a minimum of 90 volts (AC or DC) to light, it's obvious the ring voltage was at least that high.
You could also make a circuit that would be triggered by the light from neon lamps to make a noisemaker sound out. This style would be called an "isolation circuit" since the only connection between the phone line and the noisemaker would be an empty air gap rather than a wired connection, thus being less of a risk to interfere with your phone system in case of a short, lightning strike, etc.
This circuit appears to be an effective solution for DIY'ers and costs FAR less than commercial solutions. Since very little current is involved, you may be able to scavenge a suitable transformer from a discarded power supply, even if the rating is different. You might even try a "wall wart" or phone charger power supply. It takes in 100 to 240 volts and outputs 5 volts DC. The most important part is the piezo buzzer, which does all the work of converting a simple voltage into a noisy sound -- a simple audio speaker will not do this, although you might get a low hum out of it.

[ParshuramG]

hello, please tell where to connect the

[fletcherjeremiah]

Connect what part?

[bruno72748]

Does anyone know what the voltage rating for the rectifier?

[fletcherjeremiah]

Hello! We're using the rectifier on the low voltage side of the transformer, so the voltage rating should be about or a little higher than the voltage on that side. I believe mine was 12v, but a 50v rectifier should work as well.

[bscgvrvr]

Something is missing in this circuit. There is no connection betwen a telephone line and the buzzer.

[Hammerhead46]

The transfomer primary is connected to the phone line through the DC blocking capacitor.

it passes the AC signal (RING) to the buzer circuit.

[Hammerhead46]

Nice job.

The telephone line does not have 120 volts AC though.

it is 50 vdc when on hook, about 5 volts dc when off hook

BUT IT IS 50 VOLTS AC AT 25 CPS (Cycles Per Second ) in RING MODE.

IF you get bit by that YOU WILL NEVER EVER FORGET IT!

That transformer most likely go up in smoke in a couple of years with a lot of use due to being designed for 60 Hz (CPS old school as I learned it) and 25 Hz is EXTREMELY HARD on it.

But job for a first try and if it works Fantastic.

We all start someplace and the learning curve can be frustrating, I have been in electronics for 60+ years and I learn something new every day..

[nwonharp]

Hey , hammerhead

For best impedance match , thus efficiency , I agree , a transformer should be designed for the frequency it is operated at . For BEST EFFICIENCY at lower Hz , the iron core needs to be heavier . Power transformers designed for European use ( 50 Hz , as compared to American 60Hz ) will sometimes weigh more . In this application , a low current phone ringer , the effect of frequency would be negligible . Actually , in a PA system in a building ( a 70V line , and older 25V line systems ) where there are many speakers in different rooms , A transformer of similar design , at each speaker , is used to pass ( most of ) the entire audio frequencies , using different taps on the primary of each transformer at the speaker for the desired loudness levels at each speaker . :

https://en.wikipedia.org/wiki/Constant-voltage_spe...

BTW , Years ago , back when I used " land line " telephones , I built a few external " ringers " . As long as you use a suitable capacitor to block the DC from the phone line , and just use the higher voltage AC " ringer " signal to make it work , there are lots of things that you can do !

[SWV1787]

My grandfather made something like this for at their lake front property. There was about 108 steps from the house to the water's edge.
He used a buzzer he salvaged from the shop where he worked. This buzzer was designed to be heard over the sound of drop forges and whenever the phone ringed the entire house would shake.
With the staircase between the dock and the house there was no way you could make it up from the lake in time to answer the phone however.