Hello All.

As some of you might know, I am building/Have built an Arduino reef controller. Everything is flawless EXCEPT (why is there always an except....) that when I run the full thing, with load on the Futurlec Opto-Four relay switched outlets, and a 20 x 4 Backlight LCD, my LCD goes wacko. Originally I had the Arduino running off a 10V 250 ma transformer (Measured loaded voltage with a multimeter), and every single time I powered up the relay boards the LCD would get screwed up. Thinking it was a power supply issue, I switched to a 10v .5 Amp transformer. Now it does it slightly less, but it is still common. USB power is about equivalent to the 500 mA supply. Do I need to use a 1 amp supply, or should I drive the LCD with a second transformer, or something else? If at all possible, I would GREATLY prefer not to use a seperate transformer for the LCD.

Also, If i need a bigger supply, any ideas where to get one??

I saw a 12v 5 amp supply on adafruit here http://www.adafruit.com/products/352, but the 12V worries me.

Sorry, I should have been clearer. The Opto-Fours are powered by a separate, 12 V transformer. The Arduino, 5 Pushbuttons, a 20 x 4 White / Blue Backlit LCD, and whatever current it takes to switch the transistors in the Opto-four are being provided by the second power supply, which plugs into the Arduino’s voltage reg. I say 12v scares me because it is towards the top of the acceptable range for the Arduino’s reg.

Basically, if the 12v supply powering the optos is off, everything works, but when I plug in that transformer, the LCD gets screwed up.

a circuit diagram would be handy

are you using smoothing/decoupling capacitors?


Are decouplers even necessary when the 12v is isolated by opto-isolators?

The boards ( i have 2) are just directly hooked up to the Arduino for data and 5v; the 12v, as I said, is supplied by a separate transformer.

hmm can't actually read the words on the circuit decoupling capacitors would remove any random noise you are picking up

I read the article/page, and since the only "official" ICs I am using, outside of the Arduino itself, are in the LCD, I assume I need to decouple the LCD logic power supply, correct? And would the "usual" 47 uF and .01 uF caps work? If not, how would I determine the correct cap sizes? The equation he gives is all well and good but how do I apply it?

... the LCD gets screwed up.

Could you be a bit more specific?


The text becomes extremely dim (backlight stays perfectly lit) and is random characters and numbers.

I have a NKC electronics MegaProtoShield. The LCD is wired up exactly per Adafruit's LCD tutorial, 5V and GND going to their respective buses on the shield. All other 5v and GND is wired to these buses as well.

A month later...............

It's FIXED!!!

How, you might ask?

I routed the data line from the relay boards to the microprocessor right past a transformer. Re-routed, added a 100 uF cap on main arduino 5v supply, and a 33uF and .1 uF on the LCD power itself, all problems fixed.


I routed the data line from the relay boards to the microprocessor right past a transformer.

Which is precisely what KE7GKP was getting at when he said "Sorry, verbal descriptions are NEVER going to cut it for this kind of question. It is a matter of PHYSICALLY how things are wired together. How big the wires are, exactly how they are connected, what goes where, etc."


Revision. Fixed with a light load, if more than ~1 amp is pulled from the strip, no go. Also pumps screw it up.


Pictures :) :) :) :) :)

http://www.flickr.com/photos/58035235@N02/5967831575/in/photostream/ (Just click your way through the photostream to see all the pics of the strip. Last one is a schematic of the Relay Boards themselves.) I know the issue is that I am running a data line next to a power line, but the question is how do I fix it?

Would this shielded wrapped flat work?


Sorry if there was some confusion. The decoupling problem in the arduino is fixed. I am now asking how to route the ribbon cable through the power strip, and what cable to use. The pictures are of the power strip, which I believe is the pertinent part.

The rats nest:


Sorry the pic is blurry. I’ll try to get a better one.

Major components are noted.

Revision. Fixed with a light load, if more than ~1 amp is pulled from the strip, no go. Also pumps screw it up.

Parts that work : The code of the Ardiuno.

I saw the pictures and to my "HORROR" :astonished: , a flat multi cable too close of 120 V AC LINE... Pump = Major Inteference. Sound like to me, it's intefere with the flat cable. A "shield" cable may work ? ... May be not..May be yes.... Like gambling...

I look at the schematic ( signals from the Ardiuno ) My question is : Where in the schematic the flat cable come from ? If it came from DIRECTELY from the Ardinuo... :astonished: That is the problem !!! In my opinion, You need ..humm.."Re-build".."re-located' the opto board. AWAY from the AC line !!! Example : Opto-Board ( in a nice corner ) --->line from relays---->to AC plugs ( the other corner ).

The decoupling part is not fixed if you are still having the same problem. The entire system is the "pertinent part" when you are dealing with this kind of problem. How many ways can we say it?

Like he says. The "system" need to be re-design.

Thanks Techone.

What I am thinking in way of steps forward in getting the shielded ribbon, and trying that with the relays mounted into a project box affixed to the top of the strip. That way they are isolated from the main power. I was hoping to completely integrate the relays into the strip, but as you pointed out, the interference and the danger of short circuit is too great.