Light dependent resistors, also called photoresistors, are simply resistors whose resistance changes based on how much light is falling on them.

All of my LDRs go from close to zero ohms of resistance under very bright light, to over 200 million ohms (My LCR meter’s limit) when completely dark/covered.

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Diagram

Affiliate link ad. These look to be the same type of LDRs that I got from a couple of kits that I have.

The 555 timer wired in astable mode, charges a capacitor from the supply through resistance while the output is high. Once the capacitor reaches 2/3 supply voltage, then the output goes low and the capacitor discharges through the discharge pin to ground until it drops to 1/3 supply voltage. Output goes back high and the capacitor starts charging again.

Having a light dependent resistor between the capacitor and discharge pin means that light intensity will be the primary resistance factor that sets the timing involved for any particular value of capacitance that is being used.

Video

Quick light dependent resistor LDR controlled astable multivibrator 555 timer circuit







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Some nice low power boost converters above that I enjoyed using in a couple videos.





Don’t have this buck converter, but it looks nice.

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