Newsgroups: rec.arts.theatre.stagecraft
Subject: Re: Ring a telephone
References: <[email protected]>
[email protected] writes:

> I know this is an old topic, but I've got a specific question. A nerdy
> friend of mine has built a phone ringer by running ~70v @500 mA into
> the phone... it rings just fine. But, it doesn't ring 2 seconds on,
> four seconds off, the way a real phone does.
> 
> He wants to now add an "RC Circuit" (Resistance/Capacitance) to make
> the phone ring in cadence. How do we build this circuit?

A simple RC circuit will not do the job. 
You need a timer circuit that generates 2 seconds on and 4 secodns 
off type output signal. That signal is then used to control 
a relay that switches the power from the power source going 
to telephone and off. 
A 555 timer and one relay can nicely do this. 
I have no ready circuit designed jsut for this, but  
desiging it should not take too long. 
Basicly you take 555 timer in normal astable mode and 
then select the value fo two resistors and one capacitor.
Then connect relay to 555 output, and that should do it. 

You can find 555 timer IC links at 
http://www.epanorama.net/multi.php?search=search&keyword=555

-- 
Tomi Engdahl (http://www.iki.fi/then/)
Take a look at my electronics web links and documents at 
http://www.epanorama.net/