Liquid Level Indicator With Alarm Kit, Certification : ISI Certified

The name of the project itself suggests its application. Liquid Level Indicator With Alarm can be used for level control in hydro culture project. It is also used for kitchen purpose like detecting the level of water in washing machine. The main feature of this circuit is that it shows each level in meaningful English letters. It displays letter ‘E’ for Empty, ’L’ for Low, ’H’ for Half, ’A’ for Above Average and ‘F’ for Full Tank. The sensors for each level are immersed in tank. The other end is connected through four NOR gates N1 to N4 which uses IC 4001(IC1). The output is then given to IC 4055 (IC2) which is BCD to seven segment display driver IC. The level of fluid is indicated on 7- segment display. Also when the tank is full, the piezobuzzer raises a noticeable alarm.
About the Circuit :
As shown in the circuit diagram, when tank is low, N1 of IC1 gives output high, whereas N2, N3 are at logic zero. Their logics are applied to BCD inputs of IC2. Hence IC2 drives 7- segment display according to the BCD Code present at inputs. For low level BCD logic is ‘1010’. For this logic, display will indicate ‘L’. As the level increases, BCD logic changes, and display will indicate accordingly. That is ‘H’ for half and ‘A’ for above average. You can see the code generation table or logic table.
Note that there is no display pattern like ‘E’ or ‘F’ available from IC2. Therefore to obtain these pattern transistors T1 and T2 are used. These transistors blank out the unnecessary segments from 7- segment display. It can be seen that the letter ’E’ is generated by blanking ‘b’ and ‘c’ segments while it decodes digit ‘8’. Letter ‘F’ is obtained by blanking segment ‘b’ while it decodes letter ‘P’.
In addition the piezobuzzer connected to transistor T3 raises alarm when tank is full. In this case, N4 of IC1 gives logic high and makes T3 to conduct.
Note :

• The circuit should not be used with inflammable or highly reactive fluids.
• Indicates the level of water on 7-segment display with audible warning when level is full.