And giving inputs by connecting individual wires is a pain. Also, by no means it is obvious for me at the first glance. As I've built it, I am personally know what to look at, but for most outside people, the shining of the LEDs on the board is still cryptic. Using NOR / OR gates is not as parts/real estate efficient, and I am trying to avoid them.īuilding the Arithmetic Unit is great, but as it is there is no simple way to assess its workings. So, I am set to use these NAND gates wherever possible, with addition of AND gates where necessary. Here is an example of an XOR gate made of four NAND gates: On the photo below is the closeup on the Arithmetic board, where details of this construction method could be inferred.īy using component leads as signal pathways and connecting gates directly with them, as well as placing gates more closely and symmetrically, further compactification and reducing number of additional connecting wires is achieved. The Vcc and Gnd are on separate planes, with Vcc made as a mesh of inter soldered resistor leads on top of the circuit, and Gnd wires going under it. In the course of iterations through the time I came out with circuit layout which can be likened to "semi-cordwood" - by using 3rd dimension I had achieved much more close packaging, and simplification of wiring, in exchange to reduced repairability. And anyway I have a ton of resistors with these values, so I am using them. With the resistor values shown, the gates are not particularly fast, but on the other hand have a small power consumption. By adding additional (inverting) output stage AND gate is done.
One can make arbitrary number of inputs (within reason) by just changing the number of diodes.
Here is the schematic for 2-input NAND gate: All the circuits I am doing for this project are based on one fundamental unit logic gate: DTL invertor/NAND (depending on a number of inputs.
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