LLTP - Light Logic Transistorless Processor

My attempt to create a CPU/MPU without transistors or relays

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A processor using only handmade opto-couplers?

I am a bit behind in working with this idea but I want to recreate my IO Cardboard Computer without the use of any transistors. This project will make full use of my Light Logic gates

My interest in logic gates that did not make use of transistors started about a year and a half ago. After about six months of hair pulling, yelling and cursing I was able to create the entire Boolean logic set using just diodes and resistors. Granted the key diode is a LED and the key resistor is a CdS Photo Resistor. Granted I do not expect anyone to think that this processor build will be fast or practical but is part of a grand "What If" idea I had and Light Logic was born. Now it is time to put those logic gates to work and see if a working processor can be constructed this way.

  • Register Design Starting with the Accumulator

    Dr. Cockroach6 days ago 0 comments

    August 2, 2020 - A short video of testing out the Registers first bit.

    Ah, register memory and doing it with diodes. If the reader has followed my prior adventures with Light Logic then it is already proven that Light Logic is up to the task already. Just like with IO, The registers for the LLTP will use D-Latch circuits and each bit will require four or five gates depending on the output method I end up using. Here is the basic D- Latch Nand logic followed by the actual first bit wired and tested.

  • Let's start with the ALU

    Dr. Cockroach06/15/2020 at 00:40 0 comments

    A rather dull test demo of the finished basic ALU full 4 bit adder.

    July 31, 2020 - The clip leads have been replaced but even this circuit with the input switch panel will change as the LLTP design advances. Next up is the Accumulator Register circuit.

    July 28,2020 - Mounted the ALU/Adder to the first main panel and salvaged the input switches from IO. Next I will replace the clip leads with cables from the switches and the adder inputs. After that it will be time for the Accumulator Register.

    July 26, 2020 - I just finished wiring the full four bit Adder/ALU and all inputs and outputs are working properly. For a better presentation I will add a input switch panel and mount the ALU to the processor master panel. First section of many.

    July 19, 2020 - Three bits of the adder are wired and interconnected. All inputs and outputs are working properly.

    July 9, 2020 - Now have two bits of the adder wired and working. I have added a Not gate to each board as Led drivers for the Sum outputs and will finish connecting these next.

    July 6, 2020 - Test of the full adder. Added two Not gates as Led drivers.

    July 6, 2020 - First bit wired up with Nands and working like it should. Life is better with Nand gates ;-) I will post a short video of the test soon.

    July 6, 2020 - The front of the first adder bit. All the Nand gates are in position, tested and ready for the logic wiring.

    This is the power wiring on the back of the first adder bit. This helps make the front logic wiring easier to follow.

    July 4th, 2020 - As per usual for my style of construction. Paper fasteners on card stock. This the layout for the nine required Nand gates for the first bit.

    The typical accepted Nand logic for a full adder. Basic and easy to wire.

    July 3, 2020 -  Well, it was bound to happen. I had hoped that my stand alone Xor gate would save me a lot of gates and wiring but instead, due to logic level issues, was going to end up using more Light Logic gates than a pure Nand gate adder. So......... Starting over and going to just use Nand gates as I should have in the first place ;-)

    June 21, 2020 -  Bit 1 now has the diodes and resistors in place. Now to get the logic wiring finished up.

    June 18,2020 - Here is the first ALU bit wired up. Sum and Carry outputs are working as expected.

    June 17, 2020 - This is the state of the ALU. Two Xor gates and three Nand gates are finished for bit zero and I just need to interconnect. Then comes a series of tests.

    For the ripple carry adder I am just using a basic tried and true logic arrangement.

    Just as I started IO the Cardboard Computer with learning to get a full adder working and understanding what went on in the logic, I will begin the LLTP with a four bit full adder. There are a lot of circuit images found on the WEB and this circuit will use the well tried and true 2 XOR and 3 NAND gate arrangement for each bit. I have just finished making the needed 20 Led/CdS pairs and the next step is laying out the parts placement and wire each bit one at a time and test. As usual, brass plated paper fasteners will be used on paper card stock.

  • The seed to this idea

    Dr. Cockroach06/13/2020 at 22:24 0 comments

    Check out my Light Logic project to see how these gates function.



    #Light Logic - Diode Resistor Logic out of its cage 

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Dr. Cockroach wrote 5 hours ago point

@Tim Even stranger in my case as this project does not use any transistors. The logic being performed by a Led/CdS photo resistor pair. Nands all the way now and all is working as should. And yes, I tried to condition the levels but then as you said I ended up with just as many gates as if just going the Nand route :-)

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Yann Guidon / YGDES wrote 07/29/2020 at 18:46 point

Daaaaamn... Do you remember you can make a XOR easily with your system without having to use NANDs ? :-D

Put a diode in series with a LED between 2 signals and you have the gate ANDN (A='1' and B='0'). Then you put the LDR in parallel so you get A&/B + /A&B !

And you can make it even simpler when you do it at the LED side.

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Yann Guidon / YGDES wrote 07/29/2020 at 18:47 point

Oh my I didn't read all the logs ;-)

Sorry dude ;-)

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Yann Guidon / YGDES wrote 07/29/2020 at 18:54 point

So what is the problem with the XOR cells ?

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Dr. Cockroach wrote 07/29/2020 at 20:39 point

Thats OK, The LL XOR works great as a stand alone gate but when followed by another XOR as in a adder circuit, the voltage out for a one and a ground for a zero goes kind of wonky and is not reliable as it now stands. It was then that I decided to just make the entire build out of Nand gates knowing that they link well one to another :-) Never fear, I'll return to the LL XOR later and work on it :-)

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Tim wrote 14 hours ago point

>the voltage out for a one and a ground for a zero goes kind of wonky and is not reliable as it now stands

Sounds very familiar from all the weird XOR tricks. One cannot use these gates without a level restorer and then the advantage in reduces component count or tpd is already gone.

(Had to patch some inverters into my last project exactly due to this... Spice does not help if you don't have proper spice models of the chinese off-brand transistors you use...)

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Starhawk wrote 06/13/2020 at 22:37 point

Go for it, dude -- Godspeed :D

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Dr. Cockroach wrote 06/13/2020 at 22:39 point


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