Breadboard power rail capacitor

Discussion in 'General Electronics Chat' started by robijnix, Feb 23, 2013.

  1. robijnix

    Thread Starter New Member

    Feb 23, 2013
    7
    0
    Hello,

    I see a lot of people have capacitors over the power rails of their breadboards, and i don't really understand why?

    Thanks
     
  2. t06afre

    AAC Fanatic!

    May 11, 2009
    5,939
    1,222
    Well it depend. Can you give some examples?
     
  3. robijnix

    Thread Starter New Member

    Feb 23, 2013
    7
    0
    like here:
    http://youtu.be/R5OgK0qNpek?t=2m7s

    I'm asking because I'm building a circuit with a lot of 74HC/HCT ICs and i never place a capasitor over my rails like that.
     
  4. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    6,357
    718
    See my sigline on bypass caps.

    I usually put a 22uF on each side if they are connected, then a 0.1uF ceramic between + and - roughly every 15 spaces, and again next to the ICs.

    The rails alone will make things work mostly, but you need them close to the IC supply if you are doing ADC conversions.
     
  5. robijnix

    Thread Starter New Member

    Feb 23, 2013
    7
    0
    woh that was exactly the info i was looking for, thanks a lot.

    so if i understand this correctly, this is only really necessary if you want your voltages really precise?


    edit: and also, they become more important with higher frequentie, and large circuits?
     
  6. t06afre

    AAC Fanatic!

    May 11, 2009
    5,939
    1,222
  7. robijnix

    Thread Starter New Member

    Feb 23, 2013
    7
    0
    great info, thanks
     
  8. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    7,395
    1,607
    Large or small a bypass cap will help keep noise out of the power supply lines so it doesn't move from one area of your circuit to another.

    For the time being just assume you need them and put them in... even professionals do that, and (sometimes) go back later and take some out.
     
  9. crutschow

    Expert

    Mar 14, 2008
    13,052
    3,244
    The capacitors aren't just needed for precise voltage, they are to prevent spikes on the power line, due to the switching currents of one digital circuit, causing false triggering of another circuit. And even though the circuit may seem to work OK without them, under different conditions (temperature, supply voltage), the spikes could start to cause problems (which can be a bear to troubleshoot). So always use the recommended bypass capacitors in your circuit..

    It really has little to do with circuit size or operating frequency. The spikes are generated when the circuit switches (changes state) and the magnitude of the spike is independent of the switching frequency.
     
    bug13 likes this.
Loading...