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Playful Lights

Just three LEDs...

Playful Lights

Here’s a recipe to make LEDs produce slow, continuous light effects rather than abrupt changes normally obtained from square-wave drive signals.
If you are after really accurate control of one or more LEDs, the best option by far is pulsewidth modulation (PWM) which is usually obtained from a dedicated PWM chip or a suitably programmed microcontroller. On the other hand, if the blink frequency not terriblyimportant, other, much simpler methods are available. For example, get out two square-wave oscillators running at slightly different frequencies and mix their outputs together in an XOR exclusive-OR) logic gate. That’s all it takes to build a beat-frequency oscillator whose low-frequency output signal may be pulse-width modulated in
triangular(-ish) fashion.

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Gerber file

CAM/CAD data for the PCB referred to in this article is available as a Gerber file. Elektor Members can exclusively download these files for free as part of their Membership. Gerber files allow a PCB to be produced on an appropriate device available locally, or through an online PCB manufacturing service. Elektor recommends its business partner Eurocircuits as the company of choice for its own prototypes and volume production in selected cases.

R1,R8,R9,R10 = 1kO
R5,R6,R7 = 2k2
R2,R3,R4 = 976 1%
P1,P2,P3 = 50 preset
C1-C4 = 22µF 16V radial
C5-C8 = 100nF
D1 = LED, green, low current
D2 = LED, yellow, low current
D3 = LED, red, low current
D1,D2,D3 = RGB LED (e.g., Conrad Electronics # 185388 - 8B)
D4 = 1N4148
T1,T2,T3 = BC547
IC1 = 74HCT132
IC2 = 74HCT86
IC3 = 7805
K1 = 9-V PP3 battery with clip-on leads
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