Shiftregister goes Haywire with load on relay

Discussion in 'General Electronics Chat' started by Raphael_DK, Jul 14, 2013.

  1. Raphael_DK

    Thread Starter New Member

    Jul 14, 2013

    My first post here, so bear over with me.

    Now, my problem.

    I use a Arduino Uno with a 74HC595 Shift Register and a 5v relayboard with integrated optocouplers.

    The problem i face, is that as soon as there is load on the relay, the shift register goes haywire.

    I'm aware of that it's caused by noise, but i strugle to figure out how to wire the relay / shift register to remove that noise.

    I found following threads with solutions, but i find the schematics confusing:

    Right now the shift register is wired directly to the arduino and the relay. No rectifier, resistor or capacitor is mounted anywhere.

    My questions is:

    How should i wire it "properly" to remove all the noise / problems I'm facing.

    I know this maybe a "simple" problem to solve, but i just can't see the solution. Maybe I'm stupid? hehe..

    Thanks in advance :)
  2. MrChips


    Oct 2, 2009
    Well get a darn 0.1μF capacitor across Vcc and GND of the 74HC595 plus a 10μF cap across the power supply.

    Add a 1N4001 diode across the relay.
    ErnieM and Raphael_DK like this.
  3. Raphael_DK

    Thread Starter New Member

    Jul 14, 2013
    Thanks for the very fast answer !

    I've got both

    0.1uF 250V 104J CBB Metallized Film Capacitor


    1A 1000V Silicon Bridge/Rectifier Diode 1N4007

    But i do not have a 10µf cap, is there anything else i could use instead ?
  4. absf

    Senior Member

    Dec 29, 2010
    Is you load connected to AC mains or a higher DC voltage higher than 5V?

  5. Raphael_DK

    Thread Starter New Member

    Jul 14, 2013
    My relay is connected to the 230v AC mains.

    I still experience some problems with the solution above. Maybe because i don't have and use the 10μF cap across the power supply. ?