THE MAGENTA BOX

This is a portable ringing generator which, if connected to a phone line, will make the phone on the end of it ring. It works by using a relay as a vibrator to generate A.C. which is then stepped up by a transformer and fed through a capacitor into the phone line to make the phone ring!

YOU WILL NEED:

One 5V relay with single pole change-over (SPCO) contacts
One 6-0-6V mains transformer {KEZ SEZ: US users see text for mod.}
Two 2uF 250V non-electrolytic capacitors
One 6V lantern battery
One push-to-make switch
Wire

HOW TO MAKE IT:

The circuit diagram shows the relay in the normal state, ie when current is NOT Flowing!

           ---- SWITCH
       +---o  o-------+----------------+    +----------------+
       |              |.               |    |                |
    -------            }             6 |.  .|                |
      ---        RELAY }                }  {                  
    -------      COIL  }              0 }  {               OUTPUT
      ---              }           +----}  {             TO PHONE
    -------           |'           |    }  {               WIRES
      ---        COM  o NC         |    }  {    2*2uF 250V   
    -------   +-----o/             |   |'  `|                |
      ---     |       o NO         | 6 NOT  |   +---||---+   |
       |      |       |            |  USED  |   |        |   |
       +------+       +------------+        +---+---||---+---+

HOW TO USE IT:

Connect the output wires to a suitable beige boxing point on a phone line. {or use a modular plug - middle two pins of the US type, outer two pins of the four-way UK type}

HOW IT WORKS:

The telephone ringing voltage is about 90V rms, which is about 255V peak to peak. This circuit feeds 6V peak to peak into the 6V winding of a transformer, which should generate 240V peak to peak in the 240V primary. {So in America you will have to use a 3-0-3V transformer to get the right step-up ratio, as your mains voltage is only 120V.} The relay is wired through its own contacts. At first a current flows, so the contacts change over and the battery current now flows into the transformer instead of the relay coil. This produces a pulse of current in the other winding, which flows through the capacitors and into the phone line. Meanwhile, the relay isn't connected any more and so flies back. This produces a pulse of current in the opposite direction on the mains side of the transformer. Any phone on the line will ring while the switch is held closed. With practice you should be able to emulate the ringing sound perfectly! It will certainly confuse a few people!

disclaimer: this is for informational purposes only. no responsibility is accepted for any consequences of use or misuse of any information contained herein. any material whose source i have not acknowledged is believed to be my own - if it sounds like something you invented, just remember great minds think alike.