Radio Transmitter

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Thursday, March 26, 2009

Remote Telephone Ringer

This remote telephone bell ringer allows you to use a large (and loud) external bell in place or in addition to the built in (and rather wussy) ringer in most modern telephones. This is ideal for large outdoor areas, noisy shops or those hard of hearing. Most any large bell can be used as the circuit can be easily adjusted for various supply voltages.

Parts List

  • C1- 0.47 300V Capacitor
  • C2 - 47uF 25V Electrolytic Capacitor
  • R1 - 1K 1/4W Resistor
  • R2 - 10K 1/4W Resistor
  • R3 - 1K Pot
  • R4 - 2K 1/4W Resistor
  • Q1 - 6A, 200V TRIAC
  • Q2 - 6A, 200V SCR (106, Etc.)
  • D1 - 1N4774 Zener Diode
  • D2, D3- 1N4007 Rectifier Diode
  • U1- 4N33 Opto Isolator
  • Bell - Large Bell (Fire Bell, School Bell, Etc.)
  • Misc.- Board, Wire, Socket For U1, Case

  1. Virtually any TRIAC and SCR will work for Q1 and Q2 as long as the voltage rating is high enough. Q2 needs enough current capacity to handle the full load of the bell.
  2. To adjust R3, call the phone line on which the ringer is installed and adjust the pot until the bell begins to sound consistently.
  3. Make sure to check with local authorities before you connect a homemade device to your phone lines. Some areas mandate that only approved devices can be connected to the loop. This circuit provides an opto-isolator to prevent cosstalk between the phone line and power supply as well as to avoid ground loops.

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