LED Indicator for Emergency Lamp. Start Up Project 39


charge-indicator-2-aMost of the low cost LED Emergency lamps do not have LED indicators to show charging and load on conditions. This simple circuit solves the problem. It can be hooked in the Emergency lamp. A Green LED lights when the charging is going on and turns off when the charger is disconnected or power fails. It gives a good indication that current is flowing to the battery. A Red LED lights when the load turns on. It also indicates that charging process stopped.
Continue reading

LED Resistor Calculation


We use LED in different circuits as indicator or for lighting purpose. LED is the diode that requires minimum current and voltage for its operation. A series resistor is must for LED without which, the LED will be burned. See how an LED resistor can be selected.

LED-SERIES-RESISTOR

Tristate Battery Level Indicator


Here is a simple but useful battery level indicator to monitor the battery terminal voltage.Efficiency of the battery reflects in its terminal voltage. A good Lead Acid battery will show 13.8 volts in the fully charged state and if it is below 10 volts, the battery needs immediate charging. If the battery voltage goes above 14 volts, it is in the overcharged condition. This circuit uses a two lead bicolour LED to indicate three battery levels. If the voltage is below 10 volts, the Green part of the LED lights and if the voltage is above 14 volts, the Red part lights. If the battery voltage is between 10 to 14  volts LED remains off.

Continue reading

Unusual LED Indicator


Here is an Unusual LED indicator for the Battery. It turns on fully when the battery voltage is above 13 volts and starts to blink faintly when the voltage drops below 12 volts .Finally the LED turns off  when the voltage drops below 10 volts. Its design is unusual because the LED driver transistor is connected in an unusual way.

Continue reading

Load ON / OFF Indicator


This  circuit can indicate the ON / OFF status of AC Loads. Two high bright LEDs indicate the power ON and power OFF status of the load connected to the AC outlet. It is highly useful to avoid the wastage of electricity if devices like heater, electric iron, Soldering iron etc are switched on unnecessarily for long time.

Continue reading