Lesson · Problem 4
Decouple It Properly
The 100 nF capacitor closes a short loop at the pin. The 10 µF capacitor refills it.
Try it
Both capacitors join the same supply and the same ground. The 100 nF is the local part. The 10 µF is the bulk part, nearer the connector, and it refills the rail.
The pulse leaves the 100 nF, enters the VCC pin, and comes back on the GND pin. Both legs of that loop are short. The 10 µF is still there. It refills the rail. It is not this loop.
Why it works
A pin that switches wants charge from the nearest capacitor, out through a short path and back through a short path. The 100 nF part is that nearby capacitor. The 10 µF part sits nearer the connector and refills the rail. It does not replace the short loop.
Key takeaway
The 100 nF closes a short loop at the pin. The 10 µF refills the rail from farther away.
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