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PCB Isolation and D-Latch/Flip-Flop performance

A project log for A Discrete Transistor 7400 NAND GATE

If we did not have ICs then this is what a 7400 NAND gate would look like!

agp.cooperagp.cooper 08/01/2016 at 13:350 Comments

Well I am going to throw away those cheap Chinese PCB boards away. One mistake and the tracks lift. Horrible! But I did get the board finished and tested:

A respectable 42 ns propagation delay but not that much better than a BC548B (64 ns). It falls short of my expectation of 15 ns (as reported by others).

I think the base drain resistor probably needs adjustment. However, I don't think the board will survive a couple of rounds of resistor swaps.

I think I would be better off soldering the link wires (the rows of holes above the pin header) to convert the board into a D-Latch/Flip-Flop and testing that and then make a new board out of a better quality PCB.

In case your wondering how this fits in the with TTL: the above board is currently equivalent to two 74LS10. After the link wires are added it is 1/2 a 74LS74.

AlanX

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