Saturday, December 21, 2013
Simple LED Torch
A common problem with small torches is the short life-span both of the batteries and the bulb. The average incandescent torch, for instance, consumes around 2 Watts. The LED Torch in Fig. 1 consumes just 24 mW, giving it more than 80 times longer service from 4 AA alkaline batteries (that is, up to one months continuous service). Although the torchs light output is modest, it is nonetheless quite sufficient to illuminate a pathway for walking.
Circuit Diagram :
Fig. 1 : Simple LED Torch Circuit Diagram
The LED Torch is based on a 7555 timer running in astable mode (do not use an ordinary 555). A white LED (Maplin order code NR73) produces 400 mcd light output, which, when focussed, can illuminate objects at 30 metres. Try Conrad Electronic for what appears to be a stronger white LED (order code 15 37 45-11). A convex lens with short focal length is placed in front of the LED to focus the beam. If banding occurs at the beams perimeter, use another very short focal length lens directly in front of the LED to smooth the beam.
If a different supply voltage is preferred, the value of resistor R3 is modified as follows:
9V - 470 Ohm
12V - 560 Ohm
See my "Wind-up Torch" feature article in the October 2000 edition of Everyday Practical Electronics for a completely battery-free go-everywhere torch.
Friday, April 26, 2013
A Handy Pen Torch
This regulated dc provide is used to power two power white LEDs D4 and D6. Resistors R3 and R5 restricts the output present (and hence the light output) of IC1 and IC2 circuits respectively. Besides these parts, one purple colour LED (D2) is integrated in the primary circuit which works as a battery charging provide input indicator. Resistor R1 restricts the operating current of this LED.
Pen Torch Electronic Circuit Schematic
One very simple but dependable ac primarys powered battery charger circuit for the at hand pen torch can also be included here. Basically the pen torch circuit is a continuing current charger wired round Transistor T1 (BC636), energyed by using a 12v/350mA step down transformer and associated elementsD1, D2 and C1.
AC majors powered battery charger for the pen torch
Red LED (D3) provides a set voltage reference to the base of T1, with the assist of resistor R2. (During charging course of, Diode D1 in the primary circuit stop reverse current waft from the battery pack when charging input supply is absent.) After construction of the pen torch circuit, match the assembled unit inside of a small plastic enclosure for security and comfort.