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I created a (cool) logic gates circuit

At work, I need to have a good soldering skill. But honestly, I don't have the talent yet, so I need to practice. I asked my manager if I could practice soldering 1 hour a day, and he generously permitted me.

For my soldering practice, I want to make something out of it. I want to produce little projects using the used or cheap components that are readily available.

As my first project, I designed a logic gate circuit using transistors. The objective of the circuit is so that when I configure the 8-switch DIP switch, the circuit will be modified to a single functioning logic gate between OR, NOR, AND, and NAND gates. The 2-switch DIP switch is the two inputs. The red LED is the output (ON is 1, OFF is 0).

The 8-switch DIP switch configuration is as follows:

OR gate    00011100

NOR gate    00101110

AND gate    11000001

NAND gate    10100011

I am more comfortable using NPN transistors, but I only had two pieces of them. I needed more, so for the other two, I used PNP transistors. The rest are resistors and diodes.

It was pretty easy, but I still take pride on the fact that I designed this circuit on paper, by hand, without using a simulator to check if it works. I had a breadboard though, through which I verified that the components worked before I soldered them on the PCB board.

Of course, I did not get it at the first design. I had at least 3 major redesigns and a lot of readjustments in between. The last problem and the most challenging was that I needed 1 more switch to complete all four functioning gates without compromising one, but there were only 8 switches on the DIP switch. I could add additional switch and my problem would be solved, but I did not want to do that. I wanted to find a way to make it work using only the existing 8 switches. In the end, I did it. I was staring so hard at my design for hours, and then the solution stared back at me. Even before trying it out, the idea made me giddy in excitement. I modified the wiring, and it worked. I was so elated with joy.

And because I had lots of modifications and readjustments, the solder side turned out very messy. The wiring was bad, and the soldering was just as bad. This made me realize the importance of proper planning and good PCB design.



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