Battery Powered Night Lamp by 555 Timer

Part List

Overview

The objective of the circuit is to be able to provide a night lamp with an ultra low current consumption from a battery source in case of the absence of wall mains socket.

Terminology

• TS555 – a single CMOS timer which offers very low power consumption and high frequency where the timing remains very accurate in monostable or astable mode while providing reduced supply current spikes during output transitions, which enables the use of lower decoupling capacitors and with added features of high output current capability, high input impedance, wide voltage range, and output compatible with TTL, CMOS & Logic MOS

Circuit Explanation

The circuit is drawing a current less than 500 uA due to the voltage doubler that drives a pulsating ultra bright LED and since only 1.5 V cell is used. This makes the night lamp ensure minimum battery consumption. From an ordinary AA sized battery, the device can operate for approximately 3 months continuously while from an alkaline type of battery, it can operate for about 6 months.

To be able to switch OFF the circuit during daylight or upon the illumination of lights in the room, a phototransistor can be added optionally which will allow further current economy. This photoresistor circuitry will also allow the running time to be doubled or longer. The resistors R3 & R4 can be excluded if the option for additional photoresistor is not needed. By doing this, the Pin 4 of IC1 should be connected to the positive supply.

An approximately 4 Hz frequency square wave is being generated by 555 timer IC1. The integrated circuit can safely operate at 1.5 V supply or less if IC1 is a CMOS type. The voltage of the battery is raised to a peak due to the combination of D2 & C2 that forms a voltage doubler. The peak value is responsible for driving the LED.

An ordinary LED may be used but will result to poor intensity of light. For as long as the rating is at 100 V and 150 mA, a Schottky-barrier type of diode like 1N5819 and any model can also be used in place with an ordinary type 1N4148 diode but will also result to reduced intensity of LED because of higher voltage drop.

Application

The battery powered night lamps are widely available in the market with a wide variety of designs. They can have vivid & bright colours, exquisite designs & easy to be carried out, can be put beside the bed, and can be hung up on the wall. They can also be designed with cartoon characters with animated talking capabilities for the added entertainment feature for children.