555 Christmas Lights Project

Posted on Feb 6, 2014

This is different than the standard 555 oscillator circuit in that the LED is placed in the capacitor reset line (pin 7). By doing so, overall current is reduced and the high peak LED current does not flow out of the battery. Since the forward drop of the LED can interfere with the reset threshold voltage when the battery voltage is low, the capac

555 Christmas Lights Project
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itor charge source is via pin 3, the output. In this way, while the capacitor is rapidly resetting via pin 7, it is also being slowly discharged via pin 3 that follows pin 7. That way if the capacitor voltage has a difficult time discharging to the reset voltage (3V or lower), it has a little help via the charge source. Total current drain is in the order of 500uA. A 9V battery can power this for months. 12V is brighter but less convenient because small 12V batteries are uncommon. Each section can stand alone and has an individual reverse polarity diode. You may think that this diode may be eliminated, but destruction is instant if the battery is accidentally connected reverse. This can be assembled either in a strip of (4) or (6) flashers ” all (6) sections are bussed together. Three expresspcb. com miniboards yield a total of 18 (4) position, or 12 (6) position flashers. My prototype has (4) different LED colors, but the BOM lists (6) LED colors. Perhaps you can locate other colors you like better. I actually purchased my LEDs on eBay ”they have some good deals. C1 is 10uF for bright LEDs such as White, Blue and Green ”to help equalize brightness for dimmer LEDs, I simply piggybacked (2) 10uF capacitors to get 20uF. As a group project, students can learn how to identify, handle and solder small SMD devices, and test. The smallest device is the common 0805 size and even I (at my age) can handle this stuff. Smaller sizes...

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