This circuit can be made to produce interesting and attractive light effects using just a cluster of red LEDs and one of the green LEDs. One effect is first alternating between 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 junk box.
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 colors used do not have equal luminous intensity (expressed in millicandelas) D1 and D2 are silicon diodes and D3 and D4, germanium, with Schottky devices (BAT82) as an alternative 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.
MOSFET 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 space is inserted after the last flash, or not. Colorful and lively effects may also be obtained by using tri-color 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.
FEATURES of BAT82
- Integrated protection ring against static discharge
- Low capacitance
- Low leakage current
- Low forward voltage drop
- Very low switching time
- AEC-Q101 qualified• Material categorization: for definitions of compliance please seewww.vishay.com/doc99912
APPLICATIONS of BAT82
- General purpose and switching Schottky barrier diode
- Protection circuit
- Diode for low currents with a low supply voltage
- Small battery charger
- Power supplies
- DC/DC converter for notebooks