Generating a 20hz 90v signal phone ringer

[Michael Kennedy]

I'm trying to make a telephone ringer. What would be a good way to generate
a 20hz 90v signal. I can handle the 90v part no problem but the 20hz is an
issue. I have had thoughts of hacking one of those analog telephone adapters
(ata) for Voip service to do this. It could probably be programmed to ring
when a certain number is dialed.

Any Ideas?

 

[Ross Herbert]

I'm trying to make a telephone ringer. What would be a good way to generate
a 20hz 90v signal. I can handle the 90v part no problem but the 20hz is an
issue. I have had thoughts of hacking one of those analog telephone adapters
(ata) for Voip service to do this. It could probably be programmed to ring
when a certain number is dialed.

Any Ideas?

Firstly, do you absolutely need it to be 20Hz? I ask this because if
you are trying to ring a newer phone which uses an electronic ringer
you don't need 20Hz since they will work anywhere from 16 - 60Hz. 20Hz
is only required to operate older style electromagnetic ringers with
metal gongs, so the telco's still have to provide it as standard
because some people still have these phones.

Typical telco electronic exchange ringers these days use fairly
complex DC/AC converters using switch-mode techniques (much like you
will find in a modern sine wave DC/AC converter found with solar power
mains generating systems). For a hobbyist it is easier to use an audio
power amplifier with a 70V public address type output transformer. The
amplifier will need to have a 20Hz sine wave signal applied to its
input. You will also need to work out how to produce your required
cadence sequence and ring trip functions.

 

[Dave Plowman (News)]

I'm trying to make a telephone ringer. What would be a good way to
generate a 20hz 90v signal. I can handle the 90v part no problem but
the 20hz is an issue. I have had thoughts of hacking one of those
analog telephone adapters (ata) for Voip service to do this. It could
probably be programmed to ring when a certain number is dialed.

Simple way is an oscillator generating an approx sine wave feeding a pair
of 500mW transistors in push pull off a 12 volt supply. These drive a low
volt mains transformer in reverse. In the UK, I used a 240 - 12 volt one.
Not very efficient in electrical terms but works fine. The oscillator can
be triggered by a logic circuit to give the ring cycle as required.

 

[Dave D]

I'm trying to make a telephone ringer. What would be a good way to
generate a 20hz 90v signal. I can handle the 90v part no problem but the
20hz is an issue. I have had thoughts of hacking one of those analog
telephone adapters (ata) for Voip service to do this. It could probably be
programmed to ring when a certain number is dialed.

Any Ideas?

Very easy. A small 120v transformer with, say, a 12v secondary. Drive the
secondary with a lower voltage AC waveform than 12v to get approx 90v out.
You could use a transistor driven by a 555 timer IC running in astable mode
at 20Hz to drive the transformer. The positive rail if the 'inverter'
circuit could be supplied by a simple adjustable regulator to get the 90v
out from the transformer.

Obviously the transformer will not be very efficient at 20Hz, but it will
work well enough for this application.

Dave

 

[Arfa Daily]

I'm trying to make a telephone ringer. What would be a good way to
generate a 20hz 90v signal. I can handle the 90v part no problem but the
20hz is an issue. I have had thoughts of hacking one of those analog
telephone adapters (ata) for Voip service to do this. It could probably be
programmed to ring when a certain number is dialed.

Any Ideas?

I had an old Post Office local system ring generator that did the job very
simply. It had a transformer with a split winding on one side, and a single
winding on the other. The split windings were linked in series by a 2uF
paper capacitor, and a single diode ( IN4007 style ) was in series with one
of the outside terminals. The diode half wave rectified the mains going in,
providing the transformer with half mains frequency pulses ( 25Hz in the
UK ). The cap between the windings provided rough tuning, which took the
waveform back to something approximating a sine wave. Out of the other side
of the transformer came a reasonable sine wave at about 80v p-p.

I guess that the same thing could be reproduced now using a split primary
power transformer, with a secondary of say 40 - 0 - 40. The value of the cap
could be played with a bit for best waveshaping to suit the tranny. I doubt
that you would notice the frequency being 30Hz US or 25Hz UK

Arfa

 

[Fred McKenzie]

Very easy. A small 120v transformer with, say, a 12v secondary. Drive the
secondary with a lower voltage AC waveform than 12v to get approx 90v out.
You could use a transistor driven by a 555 timer IC running in astable mode
at 20Hz to drive the transformer. The positive rail if the 'inverter'
circuit could be supplied by a simple adjustable regulator to get the 90v
out from the transformer.

Obviously the transformer will not be very efficient at 20Hz, but it will
work well enough for this application.

Dave-

This sounds like it will probably work OK. My concern is that a 60 Hz
power transformer may have much too low of an impedance at 20 Hz.

The 555 circuit is probably stable enough for a resonant bell. There is
also the Rube Goldberg approach: One could divide the 60 Hz power line
frequency by 3. For battery-only, there is a chip that divides a 3.579545
crystal (tuned for 3.579540) to produce 60 Hz.

Fred

 

[DaveM]

I'm trying to make a telephone ringer. What would be a good way to
generate a 20hz 90v signal. I can handle the 90v part no problem but the
20hz is an issue. I have had thoughts of hacking one of those analog
telephone adapters (ata) for Voip service to do this. It could probably be
programmed to ring when a certain number is dialed.

Any Ideas?

Check out the web page at
http://www.tkk.fi/Misc/Electronics/circuits/telephone_ringer.html to get a
pretty good idea of telephone ringing at the layman's level. Check out the
ring tone generators at
http://ourworld.compuserve.com/homepages/Bill_Bowden/page11.htm#ring1.gif
for a couple of circuit examples that may actually work (I haven't built any
of them, but there's nothing blatantly wrong with the circuits as drawn).
Here's another one:
http://www.elecdesign.com/Articles/Index.cfm?ArticleID=7878

Cheers!!!
--
Dave M
MasonDG44 at comcast dot net (Just substitute the appropriate characters in
the address)

Never take a laxative and a sleeping pill at the same time!!