Westminster Chime Telephone Ringer

When I cooked up this gadget back in 1985 it was a real novelty. Years later I saw the plans for a similar device in a "Best of Circuit Cellar" book by Steve Ciarcia, a collection of reprints from his column that appeared in Byte magazine. I am presenting it here because some sub-circuits may be of interest to experimenters, particularly those who are interested in interfacing phone lines to digital devices.

The heart of the project is the AY-3-1350 melody synthesizer, a Radio Shack offering at the time, which was primarily designed for use as an electronic door bell. By programming several of the pins, you could select from an assortment of short tunes. The accompanying diagram has the chip hard wired to play the Westminster Abbey chime. The pitch and decay are also set with fixed resistors. Only the speed can be varied.

The ring detector circuit is built around a TCM 1512A by Texas Instruments. This also was once offered by Radio Shack. By the way, this chip also could be used as a stand-alone ringer with the addition of a piezo transducer. When an incoming call is sensed, the output of this circuit goes to ground.

In this application, the off-hook detector would cause the synthesizer chip to silence and reset when any phone on the line went off-hook to answer the incoming call. The output here also goes to ground. The components used in this portion are readily available.

If I was going to make something like this today, I would probably use a digital recording chip and create a custom sound, perhaps even a human voice announcing the call. The interfacing parts of the circuit could be used with a microcontroller or PC. Click here to view the schematic.