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.