This circuit is usable as a Night Lamp when a wall mains socket is not available to plug-in an ever running small neon lamp device. In order to ensure minimum battery consumption, one 1.5V cell is used and simple voltage doublers drives a pulsating ultra-bright LED: current drawing is less than 500µA. An optional Photo resistor will switch-off the circuit in daylight or when room lamps illuminate, allowing further current economy. This device will run for about 3 months continuously on an ordinary AA sized cell or for around 6 months on an alkaline type cell but, adding the Photo resistor circuitry, running time will be doubled or, very likely, triplicates. IC1 generates a square wave at about 4 Hz frequencies. C2 & D2 form voltage doublers, necessary to raise the battery voltage to a peak value able to drive the LED.
Parts:
R1 = 1M
R2 = 1M
R3 = 47K
R4 = LDR
C1 = 100nF-63V
C2 = 220uF-25V
D1 = Ultra Bright 10mm LED
D2 = 1N5819
B1 = 1.5V Battery or AA Cell
IC1 = 7555 CMos Timer IC
Notes:
* IC1 must be a CMos type: only these devices can safely operate at 1.5V supply or less.
* If you do not need Photo resistor operation, omit R3 & R4 and connect pin 4 of IC1 to positive supply.
* Ordinary LEDs can be used, but light intensity will be poor.
* An ordinary 1N4148 type diode can be used instead of the 1N5819 Schottky-barrier type diode, but LED intensity will be reduced due to the higher voltage drop.
* Any Schottky-barrier type diode can be used in place of the 1N5819, e.g. the BAT46, rated @ 100V 150mA.
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