Author Topic: Circuit needed (Read 1242 times)

mgerics · « **on:** May 19, 2009, 04:14:41 PM »

I have a tone generator that will give me a telephone ring if I close two contacts - I would like said ring fed through my pa to the plant floor -easy enough, but...

I want it to sound *only* if a certain extension in the phone system rings.
I plugged an older style phone into the extension jack, the tried to power a N/O relay by connecting the lines that feed a coil for the ringer - it pulses too fast; the relay closes and opens too fast for the tone generator to catch it.

I know there are already devices to do this that have a RJ11 jack to simply plug into a phone jack, but I'd like to try to build a (simple ?) circuit myself just for yucks.

Any hints / ideas ?

Thanks

brianb · « **Reply #1 on:** May 19, 2009, 04:39:55 PM »

I don't know about your whole design but... You might be able to put a large capacitor on the ringer signal going into the relay. The cap may be enough to smooth out the pulsing, and allow the relay to hold longer. The cap would be placed in parallel, not series with the relay...

QuikSanz · « **Reply #2 on:** May 19, 2009, 05:26:40 PM »

Good Day,

Use a small Full wave bridge rectifier then feed that to a small capacitor then resistor. Then feed that to a Opto-isolator which you can use to drive your small relay.

Chris

brianb · « **Reply #3 on:** May 19, 2009, 05:38:10 PM »

Yeah, guess you would need an AC to DC rectifier... I completely forgot it's AC... Good call...

Here is a site with some ring tone detection circuits...

http://www.tkk.fi/Misc/Electronics/circuits/telephone_ringer.html