Counter Timer

How do capacitors reduce interference?

In a lab that I just did, we used a 555 timer, a binary counter IC, and a binary-to-decimal decoder IC that led to an LED display. The LED display counts from 0 to 9 and is connected to the binary-to-decimal decoder. The LED behaved erratically but when you put a large capacitor in parallel with the DC power supply and the binary counter, it worked perfectly.
I know that it behaved erratically because of interference but why does a large capacitor stop the interference?

Current drawn from the supply changes the supply voltage. The higher the current and the faster the current pulses the more the supply voltage is perturbed. ICS and circuits connected tp the supply rail require high fast current Pulse to be drawn from the supply. Decoupling / bypass capacitors placed close to these components can supply the fast current pulses without disturbing the supply rail as much. This is a simplified answer. Supply bypassing is a technique that has had a number of technical articles devotrd to it.

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