LED Display problem.

Discussion in 'General Electronics Chat' started by darrenhopper, Apr 8, 2013.

  1. darrenhopper

    Thread Starter New Member

    Apr 8, 2013
    Hi, I have an application that has gone askew.

    I'm building a 64 nozzle animated fountain & have used an 8x8 LED matrix from eBay as an indicator mounted on the front panel.
    These LEDs have worked perfectly for development, until I connected the solenoid array & then they burned out almost immediately.

    As the controller was switching the valves the LED Columns were illuminating when only a single valve was open. Then the whole unit cooked.

    I'm not great with component level electronics & I'm sure I've made more than one mistake with the protection.

    The 64 solenoid valves are wired in a grid configuration and switched using 16 Relays.
    The 8x8 LED Matrix is connected to the same relay terminals with a 1.2k resistor on the positive (see diagram).


    The data sheet for the LED Array is not flush with details so the resistor values are just a guess.


    My questions are these:

    - Would resistors on the negative terminals help matters?
    - Should I be using different Resistor values?
    - Is my circuit woefully under protected & in need of total redesign?

    Thanks for looking in.
  2. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    It should work OK as is if you only turn one row at a time... You can turn on multiple rows but they will not be as bright as the current is shared between the multiple LEDs.

    I don't see anything destructive, basic concept is good.
  3. timescope


    Dec 14, 2011
    What supply voltage are you using ? The reverse breakdown voltage of some LEDs is about 5v.
    The back emf of the solenoid coils may be causing failure of the LEDS.

  4. darrenhopper

    Thread Starter New Member

    Apr 8, 2013
    Supply voltage is 24vDC.

    The LEDs are not necessarily switched as a row but it is possible if I switch all 8 cathodes.

    But I think "timescope", you may be on to an answer there. I'd not heard of using diodes across my coils until I asked a colleague yesterday.

    So new plan is to place reversed diodes across each of the solenoid coils & try it again.

    Thanks for the help guys.