Many thing in our daily need that can be easily by implement a simple applied technology. So our life become easy and comfort. We can make anything work automatic, or work without our intervention so if we forget to run it, or to turn off it, they will be done by their shelf.
By a simple applied technology, such as electronics, we can solve many simple problem as mentioned above. With the small dimension of electronic component and small power too, we can realize our need, such as automatic lamp, remote controller, water tank level controller.
Beside all that mention above, we can make many device that valuable to our need, such as decorative lamp, amplifier, detector etc. The simple applied electronic circuits are divided in to two groups, analog and digital circuitry.
Analog electronic circuits are those in which signals may vary continuously with time to correspond to the information being represented. Electronic equipment like voltage amplifiers, power amplifiers, tuning circuits, radios, and televisions are largely analog (with the exception of their control sections, which may be digital, especially in modern units).
In digital electronic circuits, electric signals take on discrete values, which are not dependent upon time, to represent logical and numeric values. These values represent the information that is being processed. The transistor is one of the primary components used in discrete circuits, and combinations of these can be used to create logic gates. These logic gates may then be used in combination to create a desired output from an input. In this page you can find one of the circuit.
Basically, battery charging has mean to flow DC current in to battery continue for several hour (depends on battery capacity and charging current). Charging process is stopped if the voltage of battery reached the maximum rating. At this voltage, if charging is not stopped then can make battery damage because of over heating ( battery get shorten life).
To avoid this condition, it will be better if we use automatic battery charger. System will charge the battery if its voltage drops to the lower voltage level and stops the charging process if its voltage reaches the upper voltage level.
Figure 1 is the simple example for automatic battery charger. This circuit work by the principle of voltage comparing that done by two op-amps. The low voltage level is detected by op-amp 2 and op-amp 1 detect the up voltage level. These op-amps work complementary, at a time only one op-amps has low voltage output. This low voltage (approximately zero) is used to set or clear the D flip-flop that same meaning with charging and stop charging. The lower and upper voltage level is tuned by VR1 and VR2.
Figure 1. Automatic Battery Charger Circuit.