Wiring Schematic Diagram

To set the combination Lock, connect the appropriate switches to pin 3,4,5 and 6 of the IC through the header.As an example if S1 is connected to pin 3, S2 to pin 4 , S3 to pin 5, S4 to pin 6 of the IC ,the combination will be 1234.This way we can create any 4 digit combinations.Then connect the rest of the switches to pin 2 of IC.This will cause the IC to reset if any invalid key is pressed , and entire key code has to be re entered.

When the correct key combination is pressed the out put ( relay) will be activated for a preset time determined by the capacitor C1.Here it is set to be 6S.Increase C1 to increase on time.

For the key pad, arrange switches in a 3X4 matrix on a PCB.Write the digits on the keys using a marker.Instead of using numbers I wrote some symbols!.The bad guys will be more confused by this.

Here is a very simple and low cost to build doorbell circuit using IC UM 66. The UM66 series are CMOS IC’s designed for using in calling bell, phone and toys. It has a built in ROM programmed for playing music. The device has very low power consumption.Thanks for the CMOS technology.

If S1 once the push button is pressed C1 is charged and the transistor Q2 will keep the IC playing the music till it ends.The time for the IC to play depends on discharging time of C1 which can be set by R1.Set R1 to select your time ,whether full tone or a part in one press.Transistor Q2 drives the speaker.

This simple and low cost ding dong electronic doorbell circuit is Using IC 8021-2. The IC has an in-built circuitry to produce ding dong sound each time its pin 3 is pulled low. If you try to press switch S2 a second time when the first ding dong sound is still being produed, it has no effect whatever and the two ding-dong bell sounds will be invariably produced.S1 is the ON- OFF switch.

You may either use a piezo tweeter or an 8-ohm, 500mW speaker at the output. During the standby period, the IC consumes nominal current of a few microamperes only. Therefore switch S1 may be kept closed. Each time switch S2 is pressed, ding dong sound is produced twice. If you try to press switch S2 a second time when the first ding dong sound is still being produed, it has no effect whatever and the two ding-dong bell sounds will be invariably produced.

This is a electronic doorbell circuit schematic has a very simple function and is very easy to build. This door bell circuit use a LF351 operational amplifier and other few common electronic components . When the S1 push-button is depressed an initial positive voltage is placed on the C2 and the non-inverting terminal of the LF351 operational amplifier and the circuit will oscillate at a low frequency .