Mutchus

Here is the circuit diagram of a battery level indicator .This circuit is very simple and very cheap and compact.It can be used in transistor one band,two band or three band.This circuit is also used in emergency lights and other power supply circuits. Battery levels,normal or are indicated by the green or red LED repectively.One can set the circuit for monitoring the level of the battery within 3 to 10V with the help of 10k preset. Transistor T1 is 'ON' due to the voltage divider biasing.Green LED is 'ON' as the collector of T1 is almost at ground. When voltgae drops below the preset voltage,T1 switches off as the voltage is not sufficient to bias it to "ON" state.But the voltage at the base of T2 is sufficient to switch on T2 to conduction. Thus red LED glows-indicating the under voltage state of the battery

This sensor is particularly suitable for use in small spaces, such as the petrol tank of a  motorbike. It has the advantage of not having any moving parts, unlike a conventional sensor with a float and float arm that make it difficult to fit in a tank. The sensor circuit is made from standard, inexpensive components and can be put together for little money. Petrol/Diesel Level Sensor Circuit Diagram : The operating principle is  based on  measuring  the forward volt-ages of two identical diodes (check this  first by measuring  them).  The forward voltage of a diode decreases with increasing junction temperature. lf a resistor is placed close to one of the two diodes, it will be heated slightly if it extends above the surface of the  petrol. For best results,the other diode (used for reference) should be located at the same level. lf the diodes are covered by the petrol in the tank, the heating resistor will not have any effect because it will be cooled by the petrol. An opamp comp...

The water-tank level meter de-scribed here is very simple and useful for monitoring the water level in an overhead tank (OHT). The water level at 30cm intervals is monitored and continuously indicated by LEDs ar-ranged in a meter-format. When all the LEDs are ‘off’, it indicates that the OHT is empty. When the water level reaches the top limit, the whole LED-meter begins to flash. The height at which the level-sensing electrodes are fitted is adjustable. Thus, the minimum and maximum level settings may be varied as desired. The range of the meter can also be enlarged to cater to any level. No special or critical components are used. CMOS ICs are used to limit the idle current to a minimum level. Even when all the LEDs are ‘on’, i.e. water reaches the top level, the demand on the power supply is reasonably low. Further, the extremely high input resistance of the Schmitt inverter gates reduces the input current and thus minimises the erosion of electrodes. The princi-pal part of the dev...