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Design News has its latest “Gadget freak” how to up, build a fading LED for spooky projects – “Partial to things that go bump in the night, Bill built a circuit that slowly illuminates and fades a pair of red LEDs. It consists of two op amps, one producing a slow rising and falling voltage (3 – 6V) and the other functioning as a voltage comparator. In operation, a linear 3V ramping waveform is generated at pin 1 of the LM1458 IC and buffered with an emitter follower transistor stage. Make the rate adjustable by using a 100K potentiometer in place of the 47K resistor at pin 2. Install it in a skull as a Halloween prop or if spooky things aren’t your thing, use it as a fancy power indicator for a home appliance.”Link.

Phillip Torrone

Editor at large – Make magazine. Creative director – Adafruit Industries, contributing editor – Popular Science. Previously: Founded – Hack-a-Day, how-to editor – Engadget, Director of product development – Fallon Worldwide, Technology Director – Braincraft.


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Comments

  1. DavidWS says:

    You can have a lot of fun with this circuit if you make three versions of it. Make them exactly the same, except vary the frequency ever so slightly for each one (change the 100K to 91K or 110K for the other two). Then connect the output from each circuit to the Red, Green and Blue channels of an RGB LED. You will have a very pleasing random colour-cycling display. By altering other values, you can change the speed of colour cycling. It’s really quite hypnotic. Email d.walker@zepler.org for more details if you’re interested.

  2. DavidWS says:

    You can have a lot of fun with this circuit if you make three versions of it. Make them exactly the same, except vary the frequency ever so slightly for each one (change the 100K to 91K or 110K for the other two). Then connect the output from each circuit to the Red, Green and Blue channels of an RGB LED. You will have a very pleasing random colour-cycling display. By altering other values, you can change the speed of colour cycling. It’s really quite hypnotic. Email d.walker@zepler.org for more details if you’re interested.

  3. Oracle1729 says:

    You’re right, but the component count gets out of hand for such a simple project, 3 IC’s, 3 transistors, 18 resistors, 3 caps.

    A single 8-pin MCU can do the job with no additional components.

  4. DavidWS says:

    Probably true, but I like the analogue feel to it ;o)

  5. Mr ? says:

    You could use 3 “555″ to generate the frequency and then connect one led to each output like this :

    Image

  6. Mr ? says:

    Corrected comment :

    You could use 3 “555″ to generate the frequency and then connect one led to each output like this :

    http://img242.imageshack.us/img242/42/1q23214frxj0.png

  7. Joseph says:

    Can you make it 3 seconds fade in/out, 3 seconds on, and 6 seconds off?

  8. rose ann says:

    can u send to me the pcb layout of this devie (fading red eyes)?…

  9. rose ann says:

    can u send to me the pcb layout of this devie (fading red eyes)?…