Green-Red Multi Flasher

This circuit can be made to produce interesting and attractive light effects using just a cluster of red LEDs and one of green LEDs. One effect is first alternating bet ween red  and green, and then lighting red and green together. With the exception of the triple LED devices (Rapid Electronics # 56 - 0205  for green, # 56 - 0200 for red) all parts are cheap and easy to find, possibly even in your junkbox

Green-Red Multi flasher Circuit Diagram:


The values of networks R3/C3, R4/C4 and R5/ C5 govern the length of the flashes. Using the  indicated values, these are about 18 seconds  with a 0.5 second interval.

Because the colours used do not have equal  luminous intensity (expressed in millican-delas) D1 and D2 are silicon diodes and D3 and D4, germanium, with Schottky devices (BAT82) as an alterative because they also exhibit a low forward drop of about 0.3 V. As germanium devices, look for the OA91, OA85 or AA119. If D1 and D2 are omitted, Green and Red are brighter by themselves than when on simultaneously.

MOSFE T T2 switches both LED devices on simultaneously arranging for roughly equal luminous output. The display has an integrated LDR that causes  the LEDs brightness to adapt automatically to darkness and bright light conditions. The circuit has lots of openings for experimentation and adaptation, for example, the flash rate is determined by the value of C1, while the link between the counter’s R (reset)  input and O3 output determines if a space is inserted after the last flash, or not. Colour-ful and lively effects may also be obtained by  using tri-colour LEDs with a common anode.
The power consumption of the circuit depends  largely on the LEDs used. With the Rapid LED  types shown, about 70 mA may be expected  at a 6 volts supply voltage.

Author : Ken Barry – Copyright : Elektor


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