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How to build Bells Ring Generator Circuit Schematic

2016-02-19 12:48  
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This circuit generates a dual-tone bells ringing similar to most door-bell units. It can be used in many applications other than door-bell. In the Notes below several options will be given in order to suit different needs. The circuit as shown in the diagram generates a "Ding-tone" when P1 is pressed and a "Dong-tone" when P1 is released. IC1D is the first-tone frequency generator and IC1F generates the second-tone.

Q2, Q5 and related components act as shape and decay controls of the two tones, trying to imitate as close as possible the bells sound. Their outputs are mixed (R7 & R13), filtered (C5) and boosted by a simple class-A audio amplifier (Q3 & Q4) in order to drive the loudspeaker. The amplifier is switched-on by Q1 when P1 is pressed, then is switched-off some seconds after P1 is released: this time-delay is fixed by C1 & R2. In this way the circuit will draw a negligible current when in stand-by mode.

Circuit diagram:

Bells Ring Generator Circuit Schematic-Circuit diagram


R1,R3,R7,R9,R13_10K 1/4W ResistorsR2_______________1M5 1/4W ResistorR4______________27K 1/4W ResistorR5,R11__________47K 1/4W ResistorsR6,R12_________220K 1/4W ResistorsR8_______________2M2 1/4W ResistorR10_____________33K 1/4W ResistorC1_______________2μ2 25V Electrolytic CapacitorC2______________47μF 25V Electrolytic CapacitorC3,C8___________10μF 25V Electrolytic CapacitorsC4,C7___________10nF 63V Polyester CapacitorsC5,C6__________100nF 63V Polyester CapacitorsC9_______________4μ7 25V Electrolytic CapacitorC10______________1μF 25V Electrolytic CapacitorD1-D5_________1N4148 75V 150mA DiodesIC1__________MC14106 or 40106 Hex Schmitt Inverter ICQ1_____________BC337 45V 800mA NPN TransistorQ2,Q3,Q5_______BC238 25V 100mA NPN TransistorsQ4 ____________BC327 45V 800mA PNP TransistorPH______________Photo resistor (any type) (see Notes)P1______________SPST Pushbutton (see Notes)SW1_____________SPST SwitchSPKR____________8 Ohm LoudspeakerB1______________3V Battery (two 1.5V AA or AAA cells in series etc.)Parts added to optional modification:R14____________220K 1/4W ResistorR15______________1M 1/4W Resistor


To obtain a "Ding-Dong" operation when pushing on P1, no matter when it is released, you must modify the circuit as shown in the frame placed at the low-right corner of the circuit diagram. D4 must be removed. C10 & R15 set the time-delay separating first and second tone.To obtain a one-tone-only generator, wire the circuit as in the optional modification, making the following changes:C9 = 100nF 63V Polyester Capacitor.Omit R9 to R13 & R15; C7, C8 & C10; D2, D4, D5 & Q5.Connect to negative supply pins 11 & 13 of IC1 and left open pins 10 & 12.An amusing application of this circuit wired as in the original schematic, is to use a photo-resistor in place of P1, then placing the unit near the flashing lamps of your Christmas tree. A soft bell sound may be heard at switch-on and switch-off of the lamp chosen.To obtain higher output power you may substitute R8, Q3 & Q4 with an audio amplifier IC like the LM386 or LM380. In this case power supply must be raised to 6 - 12V but at the same time R4 & R10 should be changed to adjust bell-tone frequencies.Good tone frequencies are roughly 2000 and 1650Hz respectively.When in stand-by mode, current drawing of the circuit is 200μA @ 3V supply: therefore SW1 can be omitted.

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