Why doesn't my PCB and simulation perform the same?

bmbouter said:

Attached is what I put together, and it models nicely.

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Good work.

@eetech00 how do I model U1 and U2 in your image? My 74HC** circuits are powered by the component properties, but yours also model C4 and C3 next to U1 and U2. What is U1 and U2 in your schematic exactly?

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U1 and U2 are part of U1A,B,C and U2A,B respectively. They represent the power supply pins of each IC. I use them to show the bypass cap required across each set of IC supply pins. They are simply a resistor connected between the pins of the rectanglular symbol. They aren't really intended to accurately model the supply pin behavior but are there so the caps are not forgotten.

Also I am truly curious about how you have those very nice switches. As you can see mine use individual power supplies with NMOS to simulate the switch to ground.

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I made a more advanced version of the switch because it simulates switch bounce. You'll need to fully understand spice before undertaking that. There are plenty of articles on the web. It is partly what you have shown except I use voltage controlled switches instead of mosfets, user adjustable pulse voltage sources, and noise generators. The symbol is fairly simple to make.

However, one thing I missed was to show the remaining unused inverters. They should be shown at the bottom of the schematic as U1D,U1E,U1F and each inverter input should be connected to VDD so each output is held low.