[Christoph]

I need to know how to make a fixed-line phone ring (without calling it) for an April Fool's Day prank. Any ideas?

[capmuffin]

i would say use a cell phone..or open iy up and check some of the wires and stuff out

[Como]

could always wire the ringer to a custom circuit board and wire the "phone line" to a switch and a 12V adapter...when you switch it it would ring.

if course, if you plugged htat line into another phone and hit the switch it would burn...

[Christoph]

Here's what I want do: I want to put a rotary phone in an unexpected place and have it ring only when I tell it to (ie not if someone calls), then when someone picks it up, they hear a recorded message. Playing the message is easy, but I don't know how to make it ring.
I don't want to do anything to the phone because I want the ring to be convincing and automatic (and I want to use the phone afterwards).

[Diggrr]

http://wandel.ca/homepage/phonering.html

If you have the $135 for the joke, there's the tele-q, made to make stage prop phones ring on cue.

It's a tough signal to duplicate, because a phone uses DC for dialtone, and AC for ring impulse.

[Christoph]

Originally posted by Diggrr
http://wandel.ca/homepage/phonering.html

If you have the $135 for the joke, there's the tele-q, made to make stage prop phones ring on cue.

It's a tough signal to duplicate, because a phone uses DC for dialtone, and AC for ring impulse.

Thanks Diggr. How did I know you'd be the one to answer.
edit: I meant the link, not the US$135 thingy. The wav file from that code will do nicely.

[Como]

sounds like an expensive answer to me

if it were me i'd probly take another old phone and GUT it for the parts, and slowly figure out how it works.

i used ot have a ghetto phone that liked to die, and i'd replace the pats as they went...it ended up mounted on a peice of wood

[JigPu]

OK, now take out your pocket protector and let’s get technical…
The POTS phone line, with all phones on-hook, should measure around 48 volts DC. Taking a phone off-hook creates a DC signal path across the pair, which is detected as loop current back at the central office. This drops the voltage measured at the phone down to about 3 to 9 volts. An off-hook telephone typically draws about 15 to 20 milliamps of DC current to operate, at a DC resistance around 180 ohms. The remaining voltage drop occurs over the copper wire path and over the telephone company circuits. These circuits provide from 200 to 400 ohms of series resistance to protect from short circuits and decouple the audio signals.

To ring your telephone, the phone company momentarily applies a 90 VRMS, 20 Hz AC signal to the line. Even with a thousand ohms of line resistance, this can still pack a bit of a shock so be careful when you are probing around trying to find a POTS line.

OK, so the phone has 48VDC on it normally (that is, 48VDC between the two wires running to it). When a ring is sent, that signal changes to a 90VAC @ 20Hz. All you have to do is find some way to send a 20Hz signal down your wire at "only" 90V (and then switch back to 48VDC)

JigPu

[diehrd]

Use a door bell transformer with a switch to the bell....That should be plenty to make it ring..

[Diggrr]

Originally posted by JigPu


OK, so the phone has 48VDC on it normally (that is, 48VDC between the two wires running to it). When a ring is sent, that signal changes to a 90VAC @ 20Hz. All you have to do is find some way to send a 20Hz signal down your wire at "only" 90V (and then switch back to 48VDC)

JigPu

Exactly, One second AC, 4 seconds DC etc....the fun of an analog system!

And yeah, it's an expensive solution. That's why your phone company shuts off dialtone after the line shorts more than 5 minutes. Ya think about it, their power grid is every bit just as large as the mains power grid, but without the luxury of a step down transformer at every house.
An older phone may give you the advantage of being less picky about the actual voltages. Diehrd's idea just might work.
Use the center two pins of the phone cord for your power.

[Alice]

This sounds like fun. I may try it just for kicks. Good luck to you!

[Diggrr]

Hey, wait a minute. A doorbell transformer would only be a DC output, and not make the clapper on the phone's bells oscillate back and forth. A doorbell is different, as it uses a solenoid coil to bring a weighted ringer into contact with an upper bell, and when juice is cut by releasing the button, it bounces back to the down on a spring striking the other lower bell.
A phone is different, in that the AC powers a coil (sort of a half transformer core) who's magnetism switches poles with the line frequncy, causing attaction/repulsion upon the clapper. That sends it back and forth between the two bells.
Regular AC should work, but it'd work faster than normal ringing, because it would hit each bell 60 times per second instead of 20.
120 is close enough to 90 to not cause any damge to the coil.
Maybe use a small light inline with the phone to limit the current being drawn from the wall, like maybe a neon indicator bulb or nightlight.
Drawback is that the bells would ring only when the switch is pushed, and stop only when the switch is released.

Still harder than you thought it might be, eh?

[Christoph]

Originally posted by Diggrr
Still harder than you thought it might be, eh?

I'm not dead yet.

edit: Alice, your sig rocks.

[datawraith]

this website lists the circuit you need to construct
it will allow for the message, and it will work exactly the way you want it to
good luck soldering
http://www.sm0vpo.com:800/_visitors/inst/ring-gen.htm

[EarthDog]

Damn... 4 year old thread... and the best solution lands in it... LOL

[decoste007xt]

Damn... 4 year old thread... and the best solution lands in it... LOL

LOL

[Headstand]

Originally Posted by EarthDog

Damn... 4 year old thread... and the best solution lands in it... LOL

4? That thing is over 6 1/2 years old.

[EarthDog]

Its 2010? Crap.

[Headstand]

Originally Posted by EarthDog

Its 2010? Crap.

That's okay. I signed a form today for 10/13/2009 instead of 09/13/2010.

[Bobnova]

No, you signed that a year ago :P