TTL Circuits

I have been trying to learn a little about electronics and TTL Logic. Here are some of my rough sketchings of things I've put together on a bread-board.

First, we have a basic switch to light up an LED
basic switch

Next, we see that a transistor (NPN) can be used like a switch. We see that power "flows across the top" (from the collector to the emittor) if we apply power to the base
transistor as switch

Here we see that power flows to the taking the path of least resistence. If we apply power to the base of the transistor, we create a path to ground. TTL NOT 1

Here we see two transistors acting together and the result will switch another transistor. This is an AND operation in TTL (Transistor Transistor Logic), meaning that power will only flow if transistors have power
TTL AND 1

This is an OR operation.
TTL OR 1

And here is NAND, Not-And ... power flows (taking the path of least resistence) unless both switches are closed which creates a low resistence short-cut to ground.
TTL NAND 1

Exclusive OR (XOR) is true if and only if one of the two switches are closed. Not if both. This shows that we can build XOR by combining NAND AND OR.
Logic XOR 0

XOR in TTL gets a little hard to follow.
TTL XOR 1

NOR in TTL
TTL NOR 1

XNOR in TTL
TTL XNOR 1

Here we see the logic for adding two 2-bit numbers.
two bit adder

Here we see that expressed in TTL, except that when I bread-board this, my middle bit does not behave as expected. I am debugging this.
TTL two bit adder
And here we see the above design implemented on a bread-board.
bread-board two bit adder

I hope to have more items later.

Wish us luck!

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