This example describes a use of digital circuits make electronic doorbell three tones , it can set the button , it will output sound different, so as to achieve the purpose of distinction as visitors .

Circuit Work
The electronic doorbell circuit consists of three audio coding trigger circuit , multi- tone generator and audio amplifier circuit, as shown in Figure 3-110 .

Coded trigger circuit from the button Sl-S6, the second four- input AND gate (DI, D2) integrated circuit ICI, resistors Rl-Rll and transistors Vl-V3 and so on.

Polyphonic sound generator circuit by the analog integrated circuit train IC2, light-emitting diode VLl and VL2 and the composition resistors R13-Rl5 .

Audio from the audio amplifier and speaker amplifier tubes V4 BL composition.

C For the power supply filter capacitor , GB for the battery.

The Failure to move the button when the Sl-S6 , Vl. V3 are closing , IC2 does not work, no sound in the speaker BL , doorbell at rest.

When pressed during S6 , Vl input due to high base and turn in the big end of IC2 's TRl generate low input trigger pulse , triggered by the work of the IC2 , its O / P -side output audio signals The signal is amplified by the V4 , sent the train through the speaker BL start of the " bang when " sound.

When the same time when pressing the call , and S5 , ICl U circuit within the 4 inputs Dl are high, its output can output high pulse , then V2 conduction , in the big end of IC2 's output to generate TR2 Low trigger pulse , IC2 · triggered by the work , from the O / P -side output composite audio signal, the signal is amplified by the W , the driver crossing the speaker BL ring + train started to issue a " bang when " sound.

When the same time when pressing the S1-S3 , IC1 D2 within the gate were the big end of 4 input goes high , its output has changedIs high , so that V3 turn , lost in the big end of TR4 IC2 's trigger pulse generated low , IC2 is triggered by the work, from the O / P -side output composite audio signal, the signal is amplified by the V4 , driven BL speaker issued a " whistle + sound + ringtones + orbital vehicle as " a combination of sounds.

BL train sound of the speaker issued the same time, the light-emitting diodes shining VLl and V sync shame .

Own large ring a bell , you can also press 51-53 . Family and friends rang the doorbell , you can tell them "secret" and let them press the S4 and S5. Stranger rang the doorbell at random , often only pressing a button , the nuclear doorbell S1-S5 in the press of a button, either no response, only the press 56 , the bell was audible , it is very easy to judge from the owner Passengers are strangers .

Component selection

Rl-Rl5 use 1/4W or 1/8W carbon film resistors .

C use a value greater than 6V voltage aluminum electrolytic capacitors.

VLl and shame are selected f3mm V high-brightness light emitting diodes.

Vl-V3 are selected S9013 silicon NPN transistor ; V4 use C8050 silicon NPN transistor .

ICl use CD4082 type four input AND gate IC II , IC2 use KD56024 integrated circuit .

BL use 0.25W, 8O micro- electric speaker.

S1-S6 are all made of normally open button. 56 can be installed when used in the most prominent parts, and S1-S5 apart.