Single-Cell Voltage Monitor
Monitoring battery voltage can be important in some application. Some battery monitor will be simply a continuous LED lamp which is dimming according to the voltage level. Here is presented monitoring circuit that flashing, which is more noticeable than simple dimming the light intensity.
At 1.2V, the LED begin flashing, and the flashing rate will increase as the voltage increase. [Circuit’s schematic diagram source: National Semiconductor Application Note]