Zen Phone Ringer
This project has yet to be realized. I'll need some help and advice.
Camille (my wife) works from home and finds regular phone ringers disruptive and disturbing. More so on modern electronic phones with synthesized ringers. She encountered this device at an osteopath practitioner's office.
The Tibetan Phone Bell and Timer
This product is nice, perhaps a bit pricey on our budget at $119.95US. But surely worth the features if you're not inclined to build one. But could we make our own?
How phones work
Here's a great tutorial on how phones work. This is going to be a really helpful article and reference: Understanding Telephones
Circuit Diagrams for ringers on the web?
Article on ringer circuits with circuit diagrams
Telephone Ringer Diagram
Potentially Useful Parts
Single Gong Ringer
Could this 'single gong ringer' be modified? Could it be modified to strike the gong only once per ring cycle?
Single Gong Ringer
Mechanical striker of some kind?
Would an arduino be appropriate to drive some hardware? Based on my knowledge of that platform it could work well. But why use an arduino when we can design a circuit, powered by the phone line?
Time to read the "How phones work" guide above first.
Does ModLab have a power suppply that can provide the ringer voltage for testing?
The telephone company sends a ringing signal which is an AC waveform. Although the common frequency used in the United States is 20 HZ, it can be any frequency between 15 and 68 Hz. Most of the world uses frequencies between 20 and 40 Hz. The voltage at the subscribers end depends upon loop length and number of ringers attached to the line; it could be between 40 and 150 Volts. Note that ringing voltage can be hazardous; when you're working on a phone line, be sure at least one telephone on the line is off the hook (in use); if any are not, take high voltage precautions. The telephone company may or may not remove the 48 VDC during ringing; as far as you're concerned, this is not important. Don't take chances.
Ringers are isolated from the DC of the phone line by a capacitor. Gong ringers in the United States use a 0.47 uF capacitor. Warbling ringers in the United States generally use a 1.0 uF capacitor. Telephone companies in other parts of the world use capacitors between 0.2 and 2.0 uF. The paper capacitors of the past have been replaced almost exclusively with capacitors made of Mylar film. Their voltage rating is always 250 Volts.
The capacitor and ringer coil, or Zeners in a warbling ringer, constitute a resonant circuit. When your phone is hung up ("on hook") the ringer is across the line; if you have turned off the ringer you have merely silenced the transducer, not removed the circuit from the line.
When the telephone company uses the ringer to test the line, it sends a low-voltage, low frequency signal down the line (usually 2 Volts at 10 Hz) to test for continuity. The company keeps records of the expected signals on your line. This is how it can tell you have added equipment to your line. If your telephone has had its ringer disconnected, the telephone company cannot detect its presence on the line.