Fading LEDs

Two strips of LEDs fading in a complementary manner

9V Battery-operated portable unit

Circuit diagram:

Fading LEDs


R1,R2_______________4K7  1/4W Resistors
R3_________________22K   1/4W Resistor
R4__________________1M   1/4W Resistor (See Notes)
R5__________________2M2  1/4W Carbon Trimmer (See Notes)
R6,R10,R11,R14,R15_10K   1/4W Resistors
R7,R8______________47K   1/4W Carbon Trimmers (See Notes)
R9,R13_____________27K   1/4W Resistors
R12,R16____________56R   1/4W Resistors

C1__________________1µF   63V Polyester Capacitor
C2________________100µF   25V Electrolytic Capacitor

D1-D4 etc._________5 or 3mm. LEDs (any type and color) (See Notes)

IC1_______________LM358  Low Power Dual Op-amp

Q1,Q2,Q4__________BC327   45V 800mA PNP Transistors
Q3,Q5,Q6__________BC337   45V 800mA NPN Transistors

SW1________________SPST  miniature Slider Switch

B1___________________9V  PP3 Battery

Clip for PP3 Battery

Device purpose:

This circuit operates two LED strips in pulsing mode, i.e. one LED strip goes from off state, lights up gradually, then dims gradually, etc. while the other LED strip does the contrary.
Each strip can be made up from 2 to 5 LEDs at 9V supply.

Circuit operation:

The two Op-Amps contained into IC1 form a triangular wave generator. The rising and falling voltage obtained at pin #7 of IC1 drives two complementary circuits formed by a 10mA constant current source (Q1, Q2 and Q5, Q6) and driver transistor (Q3 and Q6).
R4, R5 & C1 are the timing components: the total period can be varied changing their values. R7 & R8 vary the LEDs brightness.