This example describes a three- tone electronic doorbell , it can issue three kinds of tones , the use of the doorbell button when the three were installed on different doors , the master of hate , according to the different bell tones , you can determine which door is the visitors out .

Circuit Work

The electronic doorbell circuit consists of three- tone buttons Sl-S3, the transistor Vl, V2, speaker BL, resistors Rl-R3, capacitor Cl, C2, GB diode VD and battery components , as shown in Figure 3-109 .

51-53 were pressed , can control audio oscillator into the pipe Vl changes in the strength of base current .

By S1 , due to a buffer for Rl and Cl to use , BL issued gradually increased calls, release the S1 , the tone was gradually becomes low , resulting in rolling tones sound effects.

When by S2 , BL sound (not direct sound buffer ) , release the S2 , due to the charge on the Cl conduction Vickers held Vl , BL voice gradually decreased , resulting tone down sound effects.

When at S3 , BL voice (in this case the strongest voice ), after the release S2 , BL immediately stop sound , resulting in flat sound effects.

C2 Capacity to change the size , can change the level of the doorbell tone .

Component selection

Rl-R3 use 1/4W carbon film resistors or metal film resistors .

Cl voltage is 16V used electrolytic capacitors ; C2 use monolithic capacitors or polyester capacitors.

VD common use of germanium diodes type 2AP9 or 1N4148 " silicon switching diodes.

Vl use 3DG6 or S9013 NPN silicon transistor ; V2 -type germanium PNP transistors used 3AX31 .

BL use 0.25-0.5W, 8O speakers electric .

S1-S3 are moving together with a selection of doorbell buttons.

GB Using 3 5 batteries .