Self latching Light Logic ? YES !

A project log for Light Logic

Using a Led and CdS LDR to form inverting Photonic logic gates. The entire boolean logic set handled by resistors and diodes! Who'd'a thunk

Dr. CockroachDr. Cockroach 11/09/2018 at 01:487 Comments

It is possible. @matseng  forwarded an idea to me that does latch on and off every time. The led is a standard bright white and the CdS cell is a large 1 inch dia. cell hacked from some old 1960's equipment. Cell resistance in total dark is over 100k Ohms and when lighted comes down to less than 100 Ohms.  Also big thank you's to @Yann Guidon / YGDES  and @Morning.Star  for bringing ideas to make this all work as a package.

View under the hood. The real business end. Yes, two led's and Ldr's in there.

Here is the first video of the led latch in action.


roelh wrote 11/09/2018 at 18:17 point

To make the LED a bit less sensitive to low current levels, you might place a resistor in parallel to it.

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matseng wrote 11/09/2018 at 15:47 point

I wonder if this might work better with a low power incandescent bulb instead of a LED? Like the 1.5 volt "

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Dr. Cockroach wrote 11/09/2018 at 17:51 point

That is worth a try, I have a few of those around here somewhere.

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Dr. Cockroach wrote 11/09/2018 at 18:20 point

Tried that, so far no latch but will try again after I get back from work.

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Dr. Cockroach wrote 11/09/2018 at 11:16 point

It was those night lights that got me wondering how close they are to logic circuits yet just miss the mark by a step or two. These circuits are almost too easy yet show promise. I just wanted to see what could be done without the transistors :-)

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Ted Yapo wrote 11/09/2018 at 03:24 point

I have a photocell-controlled night light that works in just the opposite way - if you move your hand towards it, the reflected light tries to shut it off, and it ends up just oscillating.

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Yann Guidon / YGDES wrote 11/09/2018 at 03:22 point

Yes, clearly :-D

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