Producing artificial light is generally a temporary endeavor. Turn it on when needed, then switch the bulb off to save power. What if you want lights to continuously blink, perhaps providing a location beacon for some important object, or even as decoration? While your mind might jump to a solar setup, the Forever Flasher kit by LEDsales is able to run on a PP3 (AKA 9V) battery for years without any charging whatsoever.
The device is based around a CD4011 NAND gate IC, set up as an oscillator, which drives a pair of 2N7000 MOSFETs. When the first of these MOSFETs is switched on, it allows current to flow through an LED, lighting it up. This current is then stored in a capacitor, and bounced out to ground through a second LED and MOSFET.
Notably, the CD4011 is powered through a 1Mohm resistor, allowing it to operate on just 1.5µA between LED pulses. It’s quite a clever circuit setup from an efficiency standpoint.
Actual average current, with spikes when the LEDs turn on, is pegged at a few microamps. However, it should still last for years on a single battery–or “forever” in the vast majority of installations.
source https://blog.tindie.com/2022/06/forever-led-flasher-kit/
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