Generating a 20hz 90v signal phone ringer
Michael Kennedy
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?
Dave Plowman (News)
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.
--
*Hang in there, retirement is only thirty years away! *
Dave Plowman da...@davenoise.co.uk London SW
To e-mail, change noise into sound.
Dave D
"Michael Kennedy" <Mike...@remthis.comcast.net> wrote in message
news:qf2dnVFyr_b...@comcast.com...
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 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
<dave_d@dave_d.com> wrote:
> 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
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!!