I am trying to understand a RTC module from Sparkfun.

I don't understand the purpose of the capacitor in this circuit.

Schematic's Link

Here are the procduct's page and the schematics link.

Can some one please explain its purpose.


2 Answers 2


This is a slightly silly and simplistic analogy: -

The capacitor is like a flywheel on an engine - it smooths the rather sporadic pulses of energy associated with the movements of pistons and produces a more constant drive to the wheels of your vehicle.

Without a flywheel, the jolts and impulses from the pistons would be felt all over the vehicle and things might rattle and break or even fall-off in the road. In other words, without a flywheel, all parts of the vehicle feel the effect of the pistons.

If your chip didn't have a local decoupling capacitor, all the pulses of current it draws from the supply would "shake" the power supply voltage around and cause interference on all other circuits sharing the same power supply.


The capacitor is there as local decoupling for U1.

Please read. Why need the capacitors be as close as possible to the device?

  • \$\begingroup\$ So what would happen if I removed that capacitor ???? Would it still work. \$\endgroup\$
    – BharathYes
    Commented Jan 19, 2014 at 18:31
  • \$\begingroup\$ Also I don't understand the coupling effect. Can you please explain it a little more ??? I tried searching wikipedia. It says : decoupling is the prevention of undesired coupling between subsystems. \$\endgroup\$
    – BharathYes
    Commented Jan 19, 2014 at 18:34
  • \$\begingroup\$ The next sentence on Wikipedia answers this: "Noise caused by other circuit elements is shunted through the capacitor, reducing the effect it has on the rest of the circuit.". \$\endgroup\$
    – David
    Commented Jan 19, 2014 at 18:46
  • 1
    \$\begingroup\$ en.wikipedia.org/wiki/Decoupling_capacitor "The decoupling capacitor works as the device’s local energy storage. The capacitor cannot provide DC power because it stores only a small amount of energy but this energy can respond very quickly to changing current demands. " \$\endgroup\$
    – kenny
    Commented Jan 19, 2014 at 19:09
  • 1
    \$\begingroup\$ There are plenty of questions on this site about decoupling capacitors. Do a search and read some of the answers. \$\endgroup\$ Commented Jan 20, 2014 at 1:33

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.