Telephone Ringer with 556 dual timers Circuit diagramUsing articulate ellipsoidal after-effects of altered time periods, The ambit presented actuality produces campanology tones agnate to those produced by a telephone.
The ambit requires four astable multivibrators for its working. Therefore two 556 ICs are acclimated here. The IC 556 contains two timers (similar to 555 ICs) in a distinct package. One can additionally accumulate this ambit application four abstracted 555 ICs. The aboriginal multivibrator produces a ellipsoidal waveform with 1-second �low� continuance and 2-second �high� duration. This waveform is acclimated to ascendancy the abutting multivibrator that produces addition ellipsoidal waveform.
A resistor R7 is acclimated at the beneficiary of transistor T2 to anticipate capacitor C3 from absolutely absolution back transistor T2 is conducting. Preset VR1 charge be set at such a amount that the two campanology tones are heard in one second. The actual two multivibrators are acclimated to aftermath campanology tones agnate to the campanology pulses produced by the above-mentioned multivibrator stages.
When about-face S1 is closed, transistor T1 cuts off and appropriately the aboriginal multivibrator starts breeding pulses. If this about-face is placed in the ability accumulation path, one has to delay for a best time for the campanology to alpha afterwards the about-face is closed. The ambit acclimated additionally has a accouterment for applying a drive voltage to the ambit to alpha the ringing.
Note that the ambit is not meant for abutting to the blast lines. Application adapted drive chip at the ascribe (across about-face S1) one can use this ambit with intercoms, etc. Since campanology pulses are generated aural the circuit, alone a connected voltage is to be beatific to the alleged affair for ringing.
