using a capacitor

Thread Starter


Joined Jan 10, 2016
Hi all
i am making a circuit to feed 4-5 volts to my arduino mega 2560. i have a 12 volt supply coming from machine, i am using an led with 1k resistor to show the power is coming from machine, i am also using a diode to avoid any back signal from controller to machine(as machine card is sensitive). i am using a capacitor to absorb any sudden voltage surges to avoid any damage to my controller. i have designed a circuit in protius can u ppl have a look at it and tell me is it okay or not?


Joined May 19, 2014
Welcome to the forum.

Your circuit looks fine except that the 7805 will need a .1uF capacitor from pin 1 to ground. This will guarantee that regulator will be stable. Both this capacitor and C1 should be located close to the 7805. You may need a heat sink on the 7805.


Joined Apr 24, 2011
I don't think you want D1 where it is. It is going to decrease the 5V supplying your Arduino and does little to protect the "machine" anyway.

I am not sure of the need for it, but if I was to use it I would place it in series with the 12V input.

And welcome to the forums!


Joined Sep 9, 2010
I guess I'm the only one that ever follows the data sheet. They usually recommend a diode reverse biased across the regulator so that, if the power is removed, the capacitor C1 can discharge through the diode instead of the 7805. The fact that so many people get away with leaving the diode out tells me that it's not crucial.


Joined Aug 1, 2013
If you are concerned about a possible reverse connection to the power source, move D1 to the input side of the 7805. Also, if the wire or trace length from the DC power source to pin 1 is more than about 6 inches, add an electrolytic cap the the input next to the 0.1 uF Les recommended. Something in the 10 uF to 100 uF range.