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Light Logic meets Audio

A project log for LIGHT LOGIC - HIC SVNT DRACONES

Using a LED/LDR pair to form inverting Photonic logic gates. The entire Boolean logic set handled by resistors and diodes! Who'd'a thunk

dr-cockroachDr. Cockroach 10/30/2018 at 22:372 Comments

Update Nov 2, 2018 - I decided I had better move some things around to hear if I was truly increasing signal gain with the Light Logic circuit. I connected a 8 Ohm speaker directly to the radio ( Walkman style ) output and had to place my ear directly on the speaker to hear anything. I next connected the transformer and speaker to the radio and could hear the audio but faintly from a few feet away. I at last connected the speaker and transformer to the Led/Ldr circuit and the audio signal can be heard across the room.  There is a clear case of signal gain going on here but I still need to accurately measure it and there is a slight bit of distortion on the final output from the speaker. The Led voltage has to be adjusted for best volume/quality, not the brightest setting and the Ldr voltage has a very broad range from about 4 volts to over 12 volts with very  little overall effect.

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This idea might not pan out but I had to try it and it shows promise. Using the Led and CdS cell to not only couple two audio stages but to perhaps amplify as well. The test feeds audio from a radio to the LED / LDR coupler stage and then sends it on to a normal amplifier but I need to perform further testing/measuring to know if any pre-amplification is taking place around the Led/Ldr circuit as voltage gain. There are several passive preamps / conditioners on the market but I want to mess with this circuit a little then get back to the logic games.


Discussions

Dr. Cockroach wrote 11/07/2018 at 08:13 point

Thanks Ted, that is something I had not given any thought to. When I get back to the audio setup I will look into that :-D

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Ted Yapo wrote 11/07/2018 at 02:48 point

I wonder if you could linearize the transfer function and reduce the audio distortion by using a second CdS cell (also coupled to the LED) to add negative feedback to the LED brightness.  I'm sure you could do it with an op-amp, but that sounds like cheating here.  So, now I wonder if you could put the additional CdS cell across the LED for the negative feedback - maybe you'd need to add some kind of fixed resistor network to get it right, but I think it could work.

Of course, it would reduce the gain, which may be really what you're after, but for audio, I think it might be worth the cost.

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