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Topic: Working LCD goes blank (Read 9726 times) previous topic - next topic


The arduino keeps running, PWM outputs and relays keep working like a charm the only thing is the display


So it sounds like an intermittent connection to the display's power line.


I think I'm still using too much current. This morning te fault was intermittent (3 relays off, 1 on) @8am all relays were activated and the display blanked out completely, no random characters or intermittent blanking... I don't know how to add more power to the arduino since I'm now using 3PWM, 4 DOutputs, LCD and I2C communication for the RTC... The relays are being activated with an external PS


I think I'm still using too much current.

If it were too much current then the supply voltage would droop. You are not seeing that are you?


The 15v PS that powers the arduino does haves voltag drop, I haven't tested with the new 5v PS but before it would drop around 0.8v when a relay was activated... The 5v from the arduino did not drop (never) only the 15v PS...


Yes but 0.8V is not going to affect the voltage out of the regulator so that bit doesn't matter.


I'll check the connections to the LCD tonight, but it's odd that it will run the hello world example without a problem... Could a short create this sort of behavior? I'll also double check connections


Got home today and the screen was still blank, when the relays shut down the lCD started working again.. So it's definitely the relays... I'm going to power thn with some transistors see if it helps..
What's odd is that these relays have an inverted logic so when they are all on (blank LCD) the outputs are set to LOW, which means no current demand.. Anyone know what can cause this?


Given that the example works, I would think everything is hooked up ok, and other hardware too since it works without the display. But everything together creates the fault...

I had a similar fault when I was using an LCD shield together with a servo and powering my Uno with USB power.  If I split power so the servo was powered by a separate power supply (and connecting the two grounds), it worked well.

Me too, and using a DMM didn't detect the volt drop. I needed a scope to see it as it was so brief but enough to reset the arduino or just screw it up. It wasn't a supply issue in that the supply could deliver far more than was being drawn. ANyway a 100uF cap over the power lines was enough to fix it. I should add this was actually a bare min arduino. chip, crystal and caps.

MichaelMeissner did you add that 100uF cap as Mike suggested?



Thanks for the reply! No I haven't been able to add the 100uF cap ... Been getting late off work and te store is closed. I'll add it by Saturday probably Ansley you know how it goes, did you add a ceramic cap or what type? I've always added ceramic caps for noise elimination just wanted to make sure:::



As it goes I added a Electrolytic Cap 100uF right next to the arduino chip, it was to overcome the inrush current on some motors that was pulling the voltage down at startup. May not fix your problem but it can't hurt to try.


It Never hurts to add both. The big one for power supply spikes and the little one for noise. For relays and servo's 470uF is a better value whether you use a separate supply (highly recommended) or a single big one for all. I've never seen a piece of equipment not work because of too much by passing, I have had many of my own devices fail because "I didn't think it was going to be noisy". Over the years I have come to learn that It's a lot easier to make a place for a part on a PCB and not use it than it is to need a place to put a part and have no place to put it.

--> WA7EMS <--
"The solution of every problem is another problem." -Johann Wolfgang von Goethe
I do answer technical questions PM'd to me with whatever is in my clipboard


Its up and running! I added 6 caps total, since its hard or me to have time todo this I went ahead and added all of them at once...

1x470uF cap to each power supply.
1x100uF cap to each relay input.

Worked like a charm, thanks to everyone!


So it failed :( today around 1pm the LCD went crazy and then blank... Kind of giving up...


Figured it out last weekend... The arduino is in a high humidity area and after a while the relays would short with an aluminum case next to them causing the fault... Used some tape to isolate everything and ta-da

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