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Circuits designed by David Johnson, P.E.
Last Updated on: Wednesday, October 18, 2017 05:04 AM

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More  LED Circuits;   Flasher Circuit

Battery Free LED Flasher

LED flashers have been used for a wide variety of applications.  Some flasher units have been used in food and hardware stores, to draw attention to sale items and are often attached to boxes which dispense product discount coupons. Typically, as the illustration below depicts, these simple units have a red LED, on each side of the housing.  Inside, is a battery and flasher circuit.  The housing also has space for rolls of preprinted sale coupons.  But, the batteries powering the flashing LEDs do have to be replaced every few months.  Since the flashing always occurs in well lit stores, there is almost always enough natural and artificial light available to power a flashing unit without using any batteries.  Instead of batteries, a small solar panel on top of the unit harvests enough energy to keep the unit flashing for as long as light is available.  A medium size super capacitor keeps the available voltage hovering around 5.6v.  This voltage allows the use of any LED color desired. I like the super bright green LEDs myself.
Sales Coupon Flasher   Sales Coupon Flasher
   
  6v Solar Panel  
Typical solar cells will produce about 400ua of current per square inch of surface area in usual store fluorescent light illumination.  A 5.6v zener diode limits the voltage to the super capacitor.
The circuit below is designed to flash two bright wide angle LEDs.  Energy needed to flash the light is drawn from the diffuse light available inside a commercial store.  A six volt solar panel on the top of the flasher assembly converts some of the light striking the solar cells to electricity which charges up a super capacitor.  The super capacitor supplies the peak current needed to flash the two LEDs. A constant current LED driver is used.  The two LEDs are wired in parallel. Each receives about 10ma of current, lasting 20ms. The flash rate is once per second.  The average current is therefore about 400ua.

Click on Drawing Below to view PDF version of Schematic

More  LED Circuits;   Flasher Circuit

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