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    uln2803 relay

    Hi all..

    I got a problem here, I create the relay board that consists of 34 coil relays (5V DC). I use AT90S2313, 74HC595, and ULN2803.

    Everything is running well until I connected the relays to AC line as switcher to light bulb.

    Everytime I switch on the relay (lamp) my relay board got error.
    please help me..

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    uln2803

    what is the error..what kind of error??
    please be specific..



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  3. #3
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    uln 2803 relay

    The problem I have is when I switch the relay the AC load causes some sort of noise or interference which travels all the way back

    So what can I do to filter or suppress or eliminate this noise? What exactly is this noise?

    One more thing, when I switch the relay with no AC load it works fine.

    Added after 1 hours 35 minutes:

    I think the 74HC595 IC is a sensitive one. Does anyone have some tips to reduce the sensitivity? or solves the problem?



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    74hc595+interference

    Do you have diodes on the relays for the BACK EMF that occurs?
    You say that it doesn't happen when not loaded, which would point to
    the AC loading. But in my opinion the diode across the relay input is the
    place to start.
    As you can see a power diode D1 (1N4001 or similar) is
    connected across the relay coil, to protect the transistor from
    damage due to the back-EMF pulse generated in the relay coil’s
    inductance when Q1 turns off.
    http://www.jaycar.com.au/images_uploaded/relaydrv.pdf



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    uln2803 based relays controller

    Quote Originally Posted by treitmey
    Do you have diodes on the relays for the BACK EMF that occurs?
    thanks for your response..

    I use ULN2803 which is Darlington Array. I think it has diode to protect from inductance (CMIIW). Do I stiil need that diode?
    This noise occurs when the relay goes closed (on) with AC loads. As I know, that relay's coil inductance occurs when the relay goes off, am I right?
    And like I said before, all relays work fine, without AC loads. even it works ok when i used DC load (small DC light bulb).



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    ac relay with diode at input

    what is the max rating of the relay contacts V/A?
    what exaclty is the kind of noise? how is it effecting your circuits? is there a glitch in the power lines? or is it reseting your controllers/circuit? what exaclty/
    could you post the schematics,if you have readily.



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    coil relay noise

    sort of reseting the controller. So when i try to light on the bulb (AC load) at the first relay, my relay board is becoming randomly switch on the relays (for example, it would be 2nd, 5th relay are on). But if i unplug the AC load from the relays, whole things are running well, I mean, i can switch on-off all the relays that I want to.
    I use HRS4H-S-DC5V relays.




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    hrs4h example circuit

    this seems to be a ground problem.
    have you provided decoupling capacitors close to all the Vcc pin of all the ICs.Preferably a MLC capacitor??


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    relay hrs4h-s-5v

    thx cameo..
    as you said, i used capacitor (plastic one, because i dun have any MLC) close to 74hc595. the problem still occured. until i separated the power supply for IC and relay board (i used 2 power supplies).

    so using capacitors and separated power supplies is the best way to solving my problem (for now).. so the next question is how to make this board, to use single power supply only..

    i will try to use MLC capacitor soon.



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    uln2803 +noise

    also try a couple of 10k pull-ups on the serial data and clock to the 74hc595.
    You may be coupling in some interference from the AC. Even before the PIC starts.
    I had a very similar problem, (when someone touched the board) but I was using the higher current TPIC6C595 to directly drive my relays.



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    tpic6c595 pic

    I have the same project. Use the CLR impuls before write data for all 595.

    My project.
    tiny13 + 74hct595 + BCR533 for relays parallel with 1N4148.


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    driving relay with uln2803.pdf

    Quote Originally Posted by treitmey
    also try a couple of 10k pull-ups on the serial data and clock to the 74hc595
    thx treitmey for your response, but i'm a newbie.. i don't know how to do that. could you explain me where to put the 10k resistor (did you mean to put 10K to across vcc and clock?) or what? and on every IC or latest IC?
    please help.. thx in advance..

    Added after 4 minutes:

    @oscar_pdx

    what is CLR impuls? Did you have same problem like me?



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    ac spikes

    CLR is Clear with negative edge signal or in another datasheet is /MR - Master Reset (active low)



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    uln2803 ac

    SOLVED!! i put 100nF caps for decoupling all ICs. and put 1uF at latch pin. my problem seems to be solved..

    thx everyone..



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    Re: uln2803 ac

    Quote Originally Posted by sanliedinata View Post
    SOLVED!! i put 100nF caps for decoupling all ICs. and put 1uF at latch pin. my problem seems to be solved..

    thx everyone..
    First, I apologize for bring this thread back -- however, I have the same issue.

    Where exactly did you place the 100nF and the 1uF caps on your schematic? Thank you in advance for any help you can provide, as I am a noob.



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