| Electronics > Projects, Designs, and Technical Stuff |
| Full Adder on a breadboard |
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| ziptol:
I've been working on making a full adder for a bit, let me know what you think! I want to build 4 bit computer and hopefully this is the first step. Tested using Arduino data pins. |
| intabits:
Nine NOR gates for one bit of the adder, each consisting of a transistor and three resistors, and all discrete components. It's sure going to be a huge number of parts to make a computer this way! Are you planning to breadboard it all, or make some PCBs (SMD?) to ease the workload (and improve reliability)? And if you do go for PCBs, it may then become practical to make it an 8 bit processor, which could be much more capable. I also wonder if there is any opportunity for optimization of the parts count for a specific logic block such as this. Maybe some resistors can be eliminated by partially merging some gates together. I haven't tried to analyze for this, so I don't know if it can be done. And I think it would be great to add LEDs at strategic points throughout, say in the collectors of Q8 and Q9. EG: a LED and 270R in series, across R22 and R27. But they would be indicating negative logic, so maybe add another transistor to get a positive logic display? Good luck! |
| donmr:
One of the first computers I worked with was made of this type of logic, Resistor-Transistor-Logic, RTL. It was a DEC PDP-10 KA10 model. They had small boards with one or two gates, or a flip-flop, etc. The boards were plugged onto backplanes that filled several 6' high 19" wide racks. So it can be done, but I'd much rather use at least 7400 series ICs, or maybe some FPGAs. |
| ziptol:
I'd like to use this as a way to introduce myself to digital electronics, and help build up my knowledge and skills along the way. (I'm still a noobie and I've got a lot to learn :) ) I'm going to start out with just doing an adder, a couple registers and some control on breadboards cause there's something really calming/cathartic for me to building things out on a breadboard, although it would be cool to try making some blocks on pcbs. |
| magic:
Perfboards are OK for small projects where it doesn't make sense to design custom PCB but you want mechanical robustness of soldered connections and full flexibility in placement and routing. Smaller transistors like 2N3904/2N3906 would be sufficient here. As for LEDs, I recommend looking for ones with built-in series resistors. They aren't very common but they exist and they make life much easier. Look for LEDs rated for standard voltages like 5V or 12V rather than the usual oddball voltages of LEDs such as 1.9V, 2.7V or 3.2V. |
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