Circuit Diagram of door bell

Doorbell Circuit

The electronic doorbell in this article is the most simplest among the advance projects in this website. There are many other benefits of the project doorbell. The circuit for the electronic doorbell here will help realize whether the visitor is in front door or in back door. More about there is two LED indicatorwith different colours which provide visual indication to check if anyone had come nor not in your absence.your absence.

PART LIST

Transistors T1,T2,T5     BC148B
T3,T4     BC158B
T6     AC128
Diodes D1,D2,D3,D4     1N4001
D5     GREEN LED
D6     RED LED
Capacitors C1,C2,C3     0.01 μF

Operation water level indicator

Operation :water level indicator
http://engineeringfourum.blogspot.com/2014/01/water-level-indicator.html

The operation of this project is very simple and can be understood easily. In our project “water level indicator” there are 3 main conditions:

1. There is no water available in the source tank.
2. Intermediate level i.e. either of 3rd to 7th level.
3. There is ample amount of water available in the source tank.

So let us discuss on the more about these 3 conditions

CONDITION 1: Water not available

When the tank is empty there is no conductive path between any of the 8 indicating probes and the common probe (which is connected to 5v+ supply) so the transistor base emitter region will not have sufficient biasing voltage hence it remains in cut off region and the output across its collector will be Vc approximately 4.2v. As in this case the microcontroller is used in the active low region (which means it considers 0-2 volts for HIGH and 3-5 volts for LOW) now the output of transistor which is 4.2v approximately will be considered as LOW by the microcontroller and hence the default value given by microcontroller to the seven segment display is 1 which indicates as the tank is empty.

CONDITION 2: Intermediate levels

Now as the water starts filling in the tank a conductive path is established between the sensing probes and the common probe and the corresponding transistors get sufficient biasing at their base, they starts conducting and now the outputs will be Vce (i.e. 1.2v-1.8v) approximately which is given to microcontroller. Here the microcontroller is programmed as a priority encoder which detects the highest priority input and displays corresponding water level in the seven segment display. In this project while the water level reaches the 7th level i.e. last but one level along with display in seven segment a discontinuous buzzer is activated which warns user that tank is going to be full soon.

CONDITION 3: Water full

When the tank becomes full, the top level probe gets the conductive path through water and the corresponding transistor gets into conduction whose output given to microcontroller with this input microcontroller not only displays the level in seven segment display but also activates the continuous buzzer by which user can understand that tank is full and can switch off the motor and save water.