Four timing controls – 12V supply, Suitable for Halloween or Christmas props
This circuit, designed on request for a Halloween prop, allows fine control of a pulsing Super Bright white LED.
The four potentiometers or trimmers will set precisely: on, off, ramp
up and ramp down time-delays respectively. Ramp up and ramp down
time-delays can be set roughly in the 1 – 15 seconds range, whereas on
and off time-delays can range from a few seconds to about one minute. A
12V battery or regulated power supply is required, provided it is
reasonably stable. Total current drawing is about 25 – 30mA when the LED reaches maximum brightness.
R1,R5,R12,R13___10K 1/4W Resistors
R2,R5___________10K 1/2W Trimmers or Lin. Potentiometers
R3______________47K 1/4W Resistor
R4______________22K 1/4W Resistor
R6_______________1K 1/4W Resistor
R7,R8,R9,R14___100K 1/4W Resistors
R10,R11__________2M2 1/2W Trimmers or Lin. Potentiometers
R15____________220R 1/4W Resistor
C1,C2__________100nF 63V Polyester or ceramic Capacitors
C3,C4___________22µF 25V Electrolytic Capacitors
C5_____________220µF 25V Electrolytic Capacitor
D1,D2________1N4148 75V 150mA Diodes
D3______________LED Super Bright white (e.g. RL5-UV2030)
Q1____________BC337 45V 800mA NPN Transistor
IC1___________LM324 Low Power Quad Op-amp IC
IC2____________4093 Quad 2 input Schmitt NAND Gate IC
- Wanting to use two white LEDs, the
second device must be wired across the Emitter of the transistor and
negative ground with its own limiting resistor wired in series, like R15
and D3 in the circuit diagram.
- If common red, yellow or green LEDs are required, please wire two of them in series, in order to present roughly the same voltage drop of one white or blue LED.
- Please note that the unused sections in both ICs must have their
inputs tied to negative ground whereas the outputs must be left open, as
shown at the bottom of the diagram.
- All time-delays can be increased by changing the value of C3 and
C4 to 47µF 25V or even higher. Please vary the value of these capacitors
only, as the values of the resistors wired to the four control pots are
rather critical and should not be changed.